Intracardiac echocardiography

This article describes currently available intracardiac ultrasound (ICE) technology contrasting it with intravascular ultrasound (IVUS) highlighting their differences. Clinical applications in the electrophysiologic and cardiac catheterization laboratory are discussed and current limitations addressed. Intracardiac echocardiography (ICE) is possible because lower frequency transducers (in contrast to higher frequency IVUS devices) have been miniaturized and mounted onto catheters capable of percutaneous insertion into the heart. These lower frequency transducers are capable of enhanced tissue penetration, permitting high-resolution 2D "whole heart" imaging. Also, with the introduction of the newest phased array transducer, Doppler hemodynamic data in addition to high resolution imaging can also be obtained. ICE facilitates electrophysiologic procedures by guiding transseptal catheterization, enabling endocardial anatomy visualization and targeting of arrhythmogenic substrate, ensuring optimal ablation electrode/tissue contact and promptly diagnosing procedural complications. Promising non-electrophysiologic applications include guidance of percutaneous closure of septal defects, percutaneous mitral balloon valvuloplasty and complex cardiac biopsy. Current limitations include monoplanar imaging, narrow field of view, and relatively large size of the catheter. Intra-cardiac imaging is now a clinical tool and has the potential to play an important role in diagnostic and therapeutic interventional procedures. Further refinement and miniaturization of these transducers, through continued technological progress, will make way for primary operator controlled, integrated ultrasound-guided interventional devices.

Segmenting high-frequency intracardiac ultrasound images of myocardium into infarcted, ischemic, and normal regions

Segmenting abnormal from normal myocardium using high-frequency intracardiac echocardiography (ICE) images presents new challenges for image processing. Gray-level intensity and texture features of ICE images of myocardium with the same structural/perfusion properties differ. This significant limitation conflicts with the fundamental assumption on which existing segmentation techniques are based. This paper describes a new seeded region growing method to overcome the limitations of the existing segmentation techniques. Three criteria are used for region growing control: 1) Each pixel is merged into the globally closest region in the multifeature space. 2) "Geographic similarity" is introduced to overcome the problem that myocardial tissue, despite having the same property (i.e., perfusion status), may be segmented into several different regions using existing segmentation methods. 3) "Equal opportunity competence" criterion is employed making results independent of processing order. This novel segmentation method is applied to in vivo intracardiac ultrasound images using pathology as the reference method for the ground truth. The corresponding results demonstrate that this method is reliable and effective.

Intracardiac echocardiography

This article describes currently available intracardiac ultrasound (ICE) technology contrasting it with intravascular ultrasound (IVUS), highlighting their differences. General and specific clinical applications, limitations and future developments of ICE are addressed. ICE is possible because lower frequency transducers (in contrast to higher frequency IVUS devices) have been miniaturized and mounted onto catheters capable of percutaneous insertion into the heart. Since the recent availability of a steerable, 5.5--10MHz phased-array catheter with full Doppler capability, these lower frequency transducers are not only capable of enhanced penetration, permitting high-resolution two-dimensional (2D) imaging but can also provide haemodynamic data. ICE facilitates electrophysiologic procedures by guiding trans-septal catheterization, enabling endocardial anatomy visualization, ensuring ablation electrode/tissue contact and promptly diagnosing procedural complications. Promising non-electrophysiologic applications include guidance of percutaneous closure of septal defects, percutaneous mitral balloon valvuloplasty and complex cardiac biopsy. Current limitations include monoplanar imaging and narrow field of view. Expanded diagnostic techniques such as tissue Doppler, multiplane, three dimensional (3D) and multimodality imaging represent future refinements. ICE is now a clinical tool. With the introduction of the newest phased-array transducer, with full Doppler capability, ICE has the potential to play an important role in diagnostic and therapeutic interventional procedures. Further refinement and miniaturization hold the key to primary operator controlled, integrated ultrasound-guided interventional devices.

Intracardiac measurement of pre-ejection myocardial velocities estimates the transmural extent of viable myocardium early after reperfusion in acute myocardial infarction

OBJECTIVES

We hypothesized that wall motion velocity during pre-ejection is proportional to the regional content of viable myocardium after reperfusion for acute myocardial infarction (AMI).

BACKGROUND

Pre-ejection wall motion consists of short and fast inward and outward movement towards and away from the center of the left ventricle (LV) and is altered during regional ischemia. This short-lived event can be accurately quantified by Doppler myocardial imaging (DMI).

METHODS

Fourteen open-chest pigs underwent 60 to 120 min of left anterior descending coronary artery occlusion followed by 30 min of reperfusion. The DMI data were collected using a phased-array intracardiac catheter (LV cavity) from ischemic and nonischemic myocardium encompassed within a plane passing through two epicardial bead markers. Peak tissue velocities during isovolumic contraction (IVC) (peak positive and peak negative), ejection (S) and early filling (E) were measured. The cardiac specimen was sliced through the epicardial markers in a plane approximating the ultrasound imaging plane. The transmural extent of necrosis (TEN) (%) was measured by triphenyltetrazolium chloride staining.

RESULTS

During ischemia, positive IVC velocity was zero in ischemic walls with TEN >20%. At reperfusion, positive IVC velocity correlated better with TEN (r = -0.94, p < 0.0001) than it did S (r = -0.70, p < 0.01) and E (r = -0.81, p < 0.01). Differential IVC (the difference between peak positive and peak negative velocity) highly correlated with TEN, during ischemia (r = -0.78, p < 0.001) and during reperfusion (r = -0.93, p < 0.0001).

CONCLUSIONS

Pre-ejection tissue velocity, as measured by intracardiac ultrasound, allows rapid estimation of the transmural extent of viable myocardium after reperfusion for AMI.

Initial experience with a steerable, phased vector array ultrasound catheter in the GI tract

BACKGROUND

EUS requires a significant capital outlay. The ability to perform high-resolution phased array scanning and Doppler interrogation by using a catheter that interfaces with a standard US console could increase the accessibility of EUS. Recently, an electronic phased-array US catheter was developed for intracardiac use. To date, this technology has not been applied to the GI tract. The aim of this study is to determine the feasibility and imaging characteristics of a new phased array scanning US catheter in the GI tract.

METHODS

Swine were placed under general anesthesia. This study used a 100 cm, 10F, torquable catheter with 4-way tip deflection to greater than 90 degrees. The catheter tip houses a phased vector array transducer with variable frequency (5.5-10 MHz) and variable focal distance. It has pulsed/color and power Doppler capability. The probe was passed through a therapeutic flexible sigmoidoscope into the upper GI tract. Acoustic coupling was achieved via a condom filled with water or by gastric water infusion. Needle visualization experiments were performed with a second endoscope (also passed per oral) with a standard EUS-guided fine needle aspiration needle.

RESULTS

Acoustic coupling was easily achieved. Resolution of the GI wall into characteristic layers (esophagus 5, stomach 7) was demonstrated. At 5.5 MHz, tissue resolution and Doppler imaging were excellent to greater than 10 cm from the transducer. A 22-gauge EUS-guided fine needle aspiration needle was easily visualized at depth greater than 4 cm. Flow in gastric, hepatic, and pancreatic parenchymal vessels approximately 1 mm diameter was visualized by using power and color Doppler.

CONCLUSIONS

This 10F array US catheter is capable of high-resolution two-dimensional imaging of the gut wall as well as high-quality Doppler imaging. The Doppler capabilities of this equipment may have new GI applications.

Supplementary eye field: representation of saccades and relationship between neural response fields and elicited eye movements

The functional organization of the low-threshold supplementary eye field (SEF) was studied by analyzing presaccadic activity, electrically elicited saccades, and the relationship between them. Response-field optimal vectors, defined as the visual field coordinates or saccadic eye-movement dimensions evoking the highest neural discharge, were quantitatively estimated for 160 SEF neurons by systematically varying peripheral target location relative to a central fixation point and then fitting the responses to Gaussian functions. Saccades were electrically elicited at 109 SEF sites by microstimulation (70 ms, 10-100 microA) during central fixation. The distribution of response fields and elicited saccades indicated a complete representation of all contralateral saccades in SEF. Elicited saccade polar directions ranged between 97 and 262 degrees (data from left hemispheres were transformed to a right-hemisphere convention), and amplitudes ranged between 1.8 and 26.9 degrees. Response-field optimal vectors (right hemisphere transformed) were nearly all contralateral as well; the directions of 115/119 visual response fields and 80/84 movement response fields ranged between 90 and 279 degrees, and response-field eccentricities ranged between 5 and 50 degrees. Response-field directions for the visual and movement activity of visuomovement neurons were strongly correlated (r = 0.95). When neural activity and elicited saccades obtained at exactly the same sites were compared, response fields were highly predictive of elicited saccade dimensions. Response-field direction was highly correlated with the direction of saccades elicited at the recording site (r = 0.92, n = 77). Similarly, response-field eccentricity predicted the size of subsequent electrically elicited saccades (r = 0.49, n = 60). However, elicited saccades were generally smaller than response-field eccentricities and consistently more horizontal when response fields were nearly vertical. The polar direction of response fields and elicited saccades remained constant perpendicular to the cortical surface, indicating a columnar organization of saccade direction. Saccade direction progressively shifted across SEF; however, these orderly shifts were more indicative of a hypercolumnar organization rather than a single global topography. No systematic organization for saccade amplitude was evident. We conclude that saccades are represented in SEF by congruent visual receptive fields, presaccadic movement fields, and efferent mappings. Thus SEF specifies saccade vectors as bursts of activity by local groups of neurons with appropriate projections to downstream oculomotor structures. In this respect, SEF is organized like the superior colliculus and the frontal eye field even though SEF lacks an overall global saccade topography. We contend that all specialized oculomotor functions of SEF must operate within the context of this fundamental organization.

Intracardiac echocardiography: newest technology

Intracardiac echocardiography, defined as ultra-sonographic navigation and visualization within large blood-filled cavities or vessels of the cardio-vascular system, has recently undergone refinement as a clinical tool through technologic advances in transducer miniaturization. Intra-cardiac ultra-sound catheters image at lower frequencies than current conventional intravascular ultrasound catheters used for intracoronary imaging. The lower imaging frequency enables greater tissue penetration, permitting whole-heart evaluation from a right-sided catheter position. Newer devices are steerable, have variable imaging frequency (5.5 to 10 MHz), and full Doppler capability (pulsed, continuous wave, and tissue Doppler). These advances have made intracardiac high-resolution imaging as well as hemodynamic assessment possible. A historical perspective, current capabilities and limitations, and potential clinical and research applications of this new imaging technique are discussed.

Personal ultrasound imager: abdominal aortic aneurysm screening

BACKGROUND

Miniaturized ultrasonographic machines (2.5-MHz curved-array transducer connected to a compact 2.6-kg console), termed personal ultrasound imagers (PUIs), may enable detection of occult abdominal aortic aneurysms (AAAs).

OBJECTIVES

Our goals were to determine whether a PUI is capable of screening for AAAs and to compare the results with an established screening examination with standard echocardiography (SE).

METHODS

One hundred twenty-five patients (aged >70 years) with hypertension who were referred for transthoracic echocardiography were enrolled. After SE, a focused screening with a PUI examination was performed by a blinded sonographer. An AAA was defined as a focal enlargement of the aorta >30 mm. Results and the length of time to image the aorta were compared for both tests.

RESULTS

We studied 64 men and 61 women (aged 76.8 +/- 5 years; mean blood pressures: systolic 145.7 +/- 18 and diastolic 78.6 +/- 10; body surface area 1.9 +/- 0.2 m(2)). The mean time for SE was 2.9 +/- 1.5 minutes and for the PUI examination was 4.6 +/- 2.3 minutes. By using SE as the gold standard, the sensitivity and specificity of the PUI were 91% and 96%, respectively. The positive predictive value of the PUI was 71%, and the negative predictive value was 99%.

CONCLUSION

A PUI can be used to screen for occult AAAs as an extension of the physical examination. Results are comparable to an established screening strategy that uses more expensive, nonportable echocardiographic equipment.

Application of a continuous regression model of restenosis to saphenous vein grafts after successful percutaneous transluminal coronary angioplasty or directional coronary atherectomy

OBJECTIVES

To evaluate a quantitative model of restenosis in patients with vein graft disease undergoing percutaneous transluminal coronary angioplasty (PTCA) or directional coronary atherectomy (DCA).

BACKGROUND

A quantitative relationship between acute gain and late loss has been developed to describe the late changes in lumen dimension after native vessel coronary intervention. This same relationship may also be seen after treatment of saphenous vein graft disease.

METHODS

Patients with native coronary artery stenoses (CAVEAT-I) or saphenous vein graft lesions (CAVEAT-II) were randomized to either DCA or PTCA, and data from these trials were analyzed retrospectively. Angiographic results of the target lesions were reviewed, and each lesion was assessed for vessel caliber and reference diameter, absolute minimal lumen diameter, percent diameter stenosis, percent stenosis of the cross-sectional area, acute gain and late loss. Linear regression models were used to determine late loss and to detect differences in angiographic outcomes.

RESULTS

Vein grafts had significantly larger reference vessel diameters than native coronary arteries; they also had significantly more acute gain and more late loss. Directional coronary atherectomy was associated with a larger acute gain in both studies. Patients undergoing DCA also experienced greater late loss although the effect was statistically significant only in the CAVEAT-I study. After adjusting for the acute gain, the treatment effect on late loss became nonsignificant in both studies.

CONCLUSIONS

In patients undergoing DCA or PTCA of saphenous vein graft narrowings, the relationship between late loss and acute gain is also demonstrated, similar to the device-independent relationships seen in native coronary lesions. In CAVEAT-II, larger degrees of acute gain were also associated with higher degrees of late lumen loss.

Depletion of bovine CD8+ T cells with chCC63, a chimaeric mouse-bovine antibody

In order to investigate the role of T cells in immune responses to infectious pathogens, depletion of individual T cell subsets using monoclonal antibodies (mAbs) is commonly undertaken. Since most mAbs are of murine origin, such depletion studies in cattle are restricted by the bovine anti-mouse antibody (BAMA) response to the mouse mAbs used for the depletions. In this study, we describe the use of antibody engineering to overcome the BAMA response. The variable region cDNA from CC63, a monoclonal mouse anti-bovine CD8 antibody, has been expressed in conjunction with bovine constant region genes to produce a mouse-bovine chimaeric antibody (chCC63). Characterisation of chCC63 showed that the antibody contained a bovine constant region and specifically bound bovine CD8+ T cells. Furthermore, chCC63 blocked the binding of the original mouse antibody, CC63, and mediated complement-dependent lysis of bovine CD8+ cells in vitro. In vivo, chCC63 depleted calves of CD8+ T cells as effectively as CC63 and provoked a BAMA response that was about one-tenth of that seen with the mouse antibody.

Fixed left ventricular outflow tract obstruction in presumed hypertrophic obstructive cardiomyopathy: implications for therapy

BACKGROUND

A subset of patients presenting with a presumed diagnosis of hypertrophic obstructive cardiomyopathy (HOCM) have a fixed left ventricular outflow tract (LVOT) obstruction. Recognition of this pathophysiologic abnormality is important in choosing therapy.

METHODS

Of patients referred for treatment of HOCM, 4 had fixed LVOT obstruction. Clinical and echocardiographic data and surgical findings were reviewed.

RESULTS

In the 4 patients with clinical features consistent with HOCM or HOCM-like conditions, echocardiography showed fixed LVOT obstruction with an early-peaking LVOT Doppler signal or absence of severe systolic anterior motion of the mitral valve. The causes of fixed obstruction included accessory mitral tissue with associated fibrous ring (1 patient), fixed subaortic tunnel stenosis (2 patients), and a discreet subaortic ridge (1 patient). After surgical relief of the fixed LVOT obstruction, all patients had relief of the ventricular outflow tract gradient.

CONCLUSIONS

Not all patients with a presumed diagnosis of HOCM have isolated dynamic LVOT obstruction but may have isolated or additional fixed obstruction. Careful two-dimensional and Doppler echocardiography are needed to identify this subset of patients who are best treated surgically.

Feasibility study: transesophageal echocardiography with a 10F (3.2-mm), multifrequency (5.5- to 10-MHz) ultrasound catheter in a small rabbit model

Transesophageal echocardiography (TEE) is useful in children with congenital heart defects. However, because of available probe size (>/=7 mm diameter), its use is limited to patients weighing more than 3 kg. The aim of this study was to determine the feasibility of TEE in a small animal model by using a 10F (3.2-mm) intravascular ultrasound tipped catheter with a monoplane (longitudinal) 5.5- to 10-MHz phased vector array transducer. Ten New Zealand White rabbits (400 to 3400 g; mean 1580 g) underwent TEE. With animals under general sedation, the probe was blindly introduced into the esophagus. All intracardiac and extracardiac structures were examined, and the images were stored and independently reviewed. All pertinent intracardiac and extracardiac structures were identified except in the 3 smallest rabbits (400 to 600 g). Doppler hemodynamics and color Doppler were possible in each animal. Frequency agility (5.5 to 10 MHz) facilitated optimization of image resolution and penetration. Certain transgastric, 4-chamber, and short-axis views were limited because of the monoplane array. No overt adverse effects were associated with the procedure. Diagnostic TEE can be performed in a small animal model with a 10F, 5.5- to 10-MHz phased vector array ultrasound catheter. Our study suggests that this system has potential in performing diagnostic TEE safely in small, even premature, neonates.

Determinants of infarct size after thrombolytic treatment in acute myocardial infarction

Both experimental and single-center clinical studies have shown that myocardium at risk, residual collateral flow, and duration of coronary occlusion are important determinants of final infarct size. The purpose of this study was to replicate these results on a multicenter basis to demonstrate that perfusion imaging using different camera and computer systems can provide reliable assessments of myocardium at risk and collateral flow. Sequential tomographic myocardial perfusion imaging with technetium-99 (Tc-99m) sestamibi was performed in 74 patients with first time myocardial infarction, who were enrolled in a multicenter, randomized, double-blind, placebo-controlled pilot study of poloxamer 188 as ancillary therapy to thrombolysis. All patients underwent thrombolysis within 6 hours of the onset of chest pain. Tc-99m sestamibi was injected intravenously at the initiation of thrombolytic therapy, and tomographic imaging was performed 1 to 6 hours later to assess myocardium at risk. Collateral flow was estimated noninvasively from the acute sestamibi images by 3 methods that assess the severity of the perfusion defect. Final infarct size was determined at hospital discharge by a second sestamibi study. Myocardium at risk (r = 0.61, p <0.0001) and radionuclide estimates of collateral flow (r = 0.58 to 0.66, all p <0.0001) were significantly associated with final infarct size. These associations were independent of the treatment center. On a multivariate basis, myocardium at risk (p = 0.003), the radionuclide estimate of collateral flow (p = 0.03), and treatment arm (p = 0.04) were all independent determinants of infarct size. Time to thrombolytic therapy showed only a trend (p = 0.10). The treatment center was not significant (p = 0.42). Myocardium at risk and collateral flow are important determinants of infarct size that are independent of treatment center. Tomographic imaging with Tc-99m sestamibi can provide noninvasive assessments of these parameters in multicenter trials of thrombolytic therapy.

Intracardiac Doppler hemodynamics and flow: new vector, phased-array ultrasound-tipped catheter

Comprehensive intracardiac Doppler examination under simultaneous direct ultrasound visualization has not been previously possible. This human feasibility study demonstrates that a new 10Fr, 3.2-mm diameter, 5.5- to 10-MHz frequency agile, phased, vector array, ultrasound-tipped catheter with 4-way tip articulation provides diagnostic, high-quality, intracardiac Doppler signals using pulsed and continuous-wave, color flow, and tissue Doppler.

Clinical assessment and management of mitral stenosis

There have been significant advances in the diagnosis and treatment of the patient with mitral stenosis over the past two decades. Two-dimensional and Doppler echocardiography have supplanted the cardiac catheterization laboratory in the diagnosis and determination of the hemodynamic severity of the stenotic mitral valve. The development of a catheter-based approach for splitting fused commissures has led to earlier indications for intervention. It is likely that with the resurgence of rheumatic fever as well as influx of immigrant populations, the incidence of mitral stenosis may increase in the twenty-first century. It is thus important for the clinician to have a complete understanding of the evaluation and treatment options for the patient with mitral stenosis in the modern-day era.

Deficits in smooth-pursuit eye movements after muscimol inactivation within the primate's frontal eye field

To evaluate smooth-pursuit (SP) function in the primate frontal eye field (FEF), microinjections of muscimol, a gamma-aminobutyric acid (GABA) agonist, were used to reversibly deactivate physiologically characterized sites in FEF. SP was severely impaired by deactivation at sites in the FEF's smooth eye movement region (FEFsem) located in the fundus and posterior bank of the macaque monkey's arcuate sulcus. These SP deficits were apparent immediately after the muscimol injection and persisted for several hours but recovered by the next day. SP was most drastically and consistently impaired for directions similar to the injected site's elicited smooth eye movement direction or to the optimal SP direction for its neuronal responses. Targets moving in these directions, usually ipsilateral to the injected hemisphere, were tracked primarily with saccades after the muscimol injection, the peak SP velocity being only 10-30% of preinjection velocity. SP in other directions, including contralateral, was less strongly affected. Initial SP acceleration in response to target motion onset was also significantly diminished, generally by approximately the same proportion as peak SP velocity. In contrast, saccades were largely unaffected by muscimol injections in FEFsem; nor was there an immediate effect on SP when control sites in the saccadic region of FEF (FEFsac) were deactivated, although a SP deficit often appeared 30-60 min after FEFsac injections, possibly reflecting diffusion of muscimol into neighboring FEFsem. These reversible SP deficits produced by muscimol inactivation within FEFsem are similar to permanent deficits caused by large aspiration lesions of FEF and indicate that inclusion of FEFsem is the critical factor determining whether FEF lesions impair SP. The severity of the reversible deficits found here indicates how extremely critical FEFsem is for normal highgain SP.

Newer advances in the diagnosis and treatment of mitral stenosis

There have been significant changes in presentation, diagnosis, and therapy of patients with mitral stenosis. Both the prevalence of mitral stenosis, as well as the type of patient now with mitral stenosis, have changed significantly over the past few decades. In patients with mitral stenosis two-dimensional and Doppler echocardiography have become the diagnostic modalities of choice. The advent of percutaneous mitral balloon valvotomy now provides a nonsurgical approach for the treatment of selected patients with mitral stenosis.

Suppression of task-related saccades by electrical stimulation in the primate's frontal eye field

Patients with frontal lobe damage have difficulty suppressing reflexive saccades to salient visual stimuli, indicating that frontal lobe neocortex helps to suppress saccades as well as to produce them. In the present study, a role for the frontal eye field (FEF) in suppressing saccades was demonstrated in macaque monkeys by application of intracortical microstimulation during the performance of a visually guided saccade task, a memory prosaccade task, and a memory antisaccade task. A train of low-intensity (20-50 microA) electrical pulses was applied simultaneously with the disappearance of a central fixation target, which was always the cue to initiate a saccade. Trials with and without stimulation were compared, and significantly longer saccade latencies on stimulation trials were considered evidence of suppression. Low-intensity stimulation suppressed task-related saccades at 30 of 77 sites tested. In many cases saccades were suppressed throughout the microstimulation period (usually 450 ms) and then executed shortly after the train ended. Memory-guided saccades were most dramatically suppressed and were often rendered hypometric, whereas visually guided saccades were less severely suppressed by stimulation. At 18 FEF sites, the suppression of saccades was the only observable effect of electrical stimulation. Contraversive saccades were usually more strongly suppressed than ipsiversive ones, and cells recorded at such purely suppressive sites commonly had either foveal receptive fields or postsaccadic responses. At 12 other FEF sites at which saccadic eye movements were elicited at low thresholds, task-related saccades whose vectors differed from that of the electrically elicited saccade were suppressed by electrical stimulation. Such suppression at saccade sites was observed even with currents below the threshold for eliciting saccades. Pure suppression sites tended to be located near or in the fundus, deeper in the anterior bank of the arcuate than elicited saccade sites. Stimulation in the prefrontal association cortex anterior to FEF did not suppress saccades, nor did stimulation in premotor cortex posterior to FEF. These findings indicate that the primate FEF can help orchestrate saccadic eye movements by suppressing inappropriate saccade vectors as well as by selecting, specifying, and triggering appropriate saccades. We hypothesize that saccades could be suppressed both through local FEF interactions and through FEF projections to subcortical regions involved in maintaining fixation.

Laparoscopic resection for diverticular disease

PURPOSE

The role of laparoscopic surgery in treatment of patients with diverticulitis is unclear. A retrospective comparison of laparoscopic with conventional surgery for patients with chronic diverticulitis was performed to assess morbidity, recovery from surgery, and cost.

METHODS

Records of patients undergoing elective resection for uncomplicated diverticulitis from 1992 to 1994 at a single institution were reviewed. Laparoscopic resection involved complete intracorporeal dissection, bowel division, and anastomosis with extracorporeal placement of an anvil.

RESULTS

Sigmoid and left colon resections were performed laparoscopically in 25 patients and by open technique in 17 patients by two independent operating teams. No significant differences existed in age, gender, weight, comorbidities, or operations performed. In the laparoscopic group, three operations were converted to open laparotomy (12 percent) because of unclear anatomy. Major complications occurred in two patients who underwent laparoscopic resection, both requiring laparotomy, and in one patient in the conventional surgery group who underwent computed tomographic-guided drainage of an abscess. Patients who underwent laparoscopic resection tolerated a regular diet sooner than patients who underwent conventional surgery (3.2 +/- 0.9 vs. 5.7 +/- 1.1 days; P < 0.001) and were discharged from the hospital earlier (4.2 +/- 1.1 vs. 6.8 +/- 1.1 days; P < 0.001). Overall costs were higher in the laparoscopic group than the open surgery group ($10,230 +/- 49.1 vs. $7,068 +/- 37.1; P < 0.001) because of a significantly longer total operating room time (397 +/- 9.1 vs. 115 +/- 5.1 min; P < 0.001). Follow-up studies with a mean of one year revealed two port site infections in the laparoscopic group and one wound infection in the open group. Of patients undergoing conventional resection, one patient experienced a postoperative bowel obstruction that was managed nonoperatively, and, in one patient, an incarcerated incisional hernia developed that required urgent laparotomy.

CONCLUSIONS

Laparoscopic resection in patients with chronic diverticulitis is safe, with faster recovery and shorter hospital stay compared with conventional open surgery. Higher cost of operating room usage time makes the laparoscopic technique difficult to justify economically. Simplification of operating room use and better case selection may improve cost-effectiveness of the laparoscopic approach.

Neurons in the supplementary eye field of rhesus monkeys code visual targets and saccadic eye movements in an oculocentric coordinate system

1. We investigated whether neurons in the supplementary eye field (SEF) of macaque monkeys code saccadic eye movements in oculocentric coordinates (relative to the current direction of fixation) or in craniocentric coordinates (relative to the head). Craniocentric coding in SEF had been previously suggested by the convergent appearance of electrically elicited saccades originating at different orbital positions. 2. We primarily studied SEF neurons that started responding before the beginning of saccades because such presaccadic activity is likely related to saccade generation and metrics. Using a memory-saccade task, we classified the presaccadic activity of each neuron as either purely visual related, purely movement related, or both visual and movement related. 3. We then mapped the response fields (receptive fields and movement fields) of SEF neurons from different orbital positions. When mapped relative to a central fixation point, the strongest responses for a given SEF neuron invariably occurred for a particular polar direction with fairly symmetrical declines for departures from that direction. When tested using other fixation point locations, their strongest responses almost always continued to occur for stimuli having the same polar direction relative to each fixation point tested, and thus they appeared to code both stimulus direction and saccade direction in an oculocentric coordinate system. 4. The effect of eye position on SEF presaccadic activity was quantified in two ways by computing, for each neuron, 1) an "intersection distance," the eccentricity of the point where extensions of the neuron's optimal polar directions measured at two eccentric orbital positions converged, and 2) an "orbital perturbation index" such that an index of 0 corresponded to no change in the neuron's optimal polar direction across different orbital positions (i.e., perfectly oculocentric response fields) and an index of 1 corresponded to optimal polar directions that converged to the same craniocentric goal regardless of initial eye position (i.e., perfectly craniocentric response fields). For neurons with both visual and movement responses, these measures were calculated separately for each type of activity using tasks that temporally separated the visual cue presentation and the saccade to it. 5. Almost all of the intersection distances were well beyond the oculomotor range (+/- 50 degrees) of the monkey (38/39 for movement activity and 62/66 for visual activity). The median intersection distance for visual activity was very large (274 degrees), and the median for movement activity was slightly divergent (beyond infinity). Thus SEF neurons rarely showed a conspicuous convergence of response field direction. 6. Likewise, the mean orbital perturbation indexes were very small (-0.04 +/- 0.21, mean +/- SD, for movement activity and 0.09 +/- 0.15 for visual activity), also indicating that SEF neurons code stimuli and saccades in an oculocentric manner. 7. For neurons with both visual and movement activities, the orbital perturbation indexes of the two activities were not significantly correlated (r = 0.16), even though their characteristic directions (optimal polar direction estimated from the center of the screen) were almost the same (circular correlation, r+ = 0.97). The lack of a significant correlation between the visual and movement activity orbital perturbation indexes is consistent with the hypothesis that most of the variation in this index represents statistically independent errors of measurement. Conversely, the strong covariation of visual and movement activity characteristic directions indicates that directional preference is a fundamental functional property of SEF presaccadic activity.(ABSTRACT TRUNCATED)

A comparison of survival at different degrees of hemorrhagic shock in germ-free and germ-bearing rats

We have previously reported superior survival after one level of hemorrhagic shock in germ-free (GF) rats compared with germ-bearing (GB) rats. The objective of this study was to determine the effect of the GF state on survival at different degrees of hemorrhagic shock. GF and GB rats were bled to a mean arterial blood pressure of 30 mmHg. Shock was terminated after 10, 20, 40, or 80% of the maximum shed blood volume was reabsorbed spontaneously. Both shock time and time to decompensation were significantly longer in GF rats (p < .05). Comparative survival was greater for GF rats at most levels of shock (p < .01). This superiority in survival was greatest at moderate shock levels and decreased at severe shock levels. There may be several reasons for the increased tolerance of GF animals to hemorrhagic shock such as metabolic or immunologic variations. It is hard to avoid the fact, however, that the most notable difference between the GF and GB rat is the presence or absence of bacteria.

Topography of projections to posterior cortical areas from the macaque frontal eye fields

Frontal eye field (FEF) projections to posterior cortical areas were mapped by autoradiography of tritiated amino acids (Leu, Pro) in six macaque monkeys. In three monkeys, the large saccade part of the FEF (IFEF) was identified by microstimulation and injected with tracers. In a fourth monkey, the small saccade part of the FEF (sFEF) was identified by microstimulation and injected with tracer. Tracer injections were placed into the sFEF region of two other monkeys using anatomical landmarks. The IFEF and sFEF generally had distinct and largely segregated projections to posterior cortical areas, and the overall pattern of labeling in visual areas with established topology indicates that IFEF neurons preferentially project to areas having large and eccentric receptive fields, whereas sFEF neurons project to areas having smaller, more centrally located fields. The terminal fields from the sFEF were more widespread than those from IFEF. Projections from sFEF terminated in the lateral intraparietal area (LIP), the ventral intraparietal area (VIP), and the parietal part of visual area V3A, in the fundus of the superior temporal visual area (FST), the middle temporal area (MT), the medial superior temporal area (MST), the temporal part of visual area V4, the inferior temporal area (IT), and the temporal-occipital area (TEO) and in occipital visual areas V2, V3, and V4. Projections from IFEF terminated in parietal areas 7a, LIP, and VIP and the medial part of parietal area PE; in temporal areas MST and the superior temporal polysensory area (STP); and in occipital area V2 and posterior cingulate area 23b. Projections from IFEF and sFEF appeared to terminate in different parts of common target areas in MST, LIP, and V2. The topography of IFEF and sFEF projections to LIP suggests that this posterior eye field may also be organized by saccade amplitude. Most terminal labeling from FEF injections was bilaminar to layers I and V/VI, but labeling in area LIP, area MT, the medial part of area PE, and area 23b was columnar-form to all layers.

Comparison of the smooth eye tracking disorder of schizophrenics with that of nonhuman primates with specific brain lesions

The smooth pursuit eye tracking deficit (ETD) often associated with schizophrenia has generated enormous interest over the last 20 years. The deficit is observed in about 80% of schizophrenics and in half of their first degree relatives. It is not affected by neuroleptic medication and is not due to inattention. A review of 52 studies (and actual records when available) on ETD in schizophrenia reveals that the deficit can consistently be described as low gain pursuit augmented with catch-up saccades and often peppered with intrusive saccades. A review of the brain areas that have been shown to be involved in pursuit provides the necessary background for the subsequent section which details the nature of the smooth tracking deficits following experimental lesions. This section reveals that the ETD following lesions of the frontal lobe is unique in that it closely resembles the ETD of schizophrenics. This finding lends further support for frontal lobe theories of schizophrenia.

Physiological correlate of fixation disengagement in the primate's frontal eye field

1. We recorded from the frontal eye field (FEF) of rhesus monkeys while they performed the gap task in which the fixation point disappears 200 ms before the appearance of the peripheral saccadic target. This gap allows the disengagement of fixation to begin before the acquisition of saccade coordinates, thereby greatly reducing saccade latency ("gap effect"). Very short-latency saccades obtained in this gap task have been called "express saccades". 2. We studied 145 FEF neurons that had presaccadic activity on conventional saccade tasks. When tested in the gap task with a 200-ms gap, nearly half of these neurons (69) increased their discharge rate in response to the disappearance of the fixation target. We call this increase a fixation-disengagement discharge (FDD). The mean latency of the start of the FDD relative to the fixation light extinction was 149 +/- 36 (SD) ms. 3. Gap-task trials with the saccade target in the cell's response field were randomly intermixed with trials having the target opposite to the cell's field. The FDD was present in both cases: on trials into the response field, the FDD was followed by the cell's presaccadic burst. On trials opposite the cell's field, the FDD activity was suppressed prior to the saccade. 4. The FDD was most likely to be found in cells that had the movement type of presaccadic activity, i.e., movement cells and visuomovement cells. FDD was observed in 57% of visuomovement cells A, B, and C, 50% with movement activity, and 18% purely visual.(ABSTRACT TRUNCATED AT 250 WORDS)

Neural responses related to smooth-pursuit eye movements and their correspondence with electrically elicited smooth eye movements in the primate frontal eye field

1. Intracortical microstimulation of a portion of the monkey frontal eye field (FEF) lying in the floor and posterior bank of the arcuate sulcus evokes smooth, rather than saccadic eye movements. To further explore this region's involvement in pursuit, we recorded from FEF neurons in the vicinity of sites from which smooth eye movements (SEMs) were elicited electrically and studied their responses during smooth-pursuit and saccadic tasks. In this report, we describe the neurons' responses during visually guided smooth pursuit and compare their locations and response properties with those of elicited SEMs. 2. One hundred and ninety-three neurons, recorded from the FEF region in six hemispheres of three rhesus monkeys, were classified as "pursuit neurons". These neurons responded during smooth-pursuit tracking of moving visual stimuli but had no, or only minimal, responses in conjunction with visually guided saccades. Pursuit neurons were located in a small region of the arcuate fundus and posterior bank that overlapped, and extended slightly beyond, the region from which SEMs were elicited with microstimulation. 3. All pursuit neurons had a preferred pursuit direction, and all directions were represented with no strong bias toward ipsilateral, contralateral, up, or down. The directional tuning of 80 pursuit cells was measured quantitatively by testing pursuit in several directions and fitting the responses to a Gaussian function. Tuning indices (the sigma parameter of the Gaussian fit) varied between 13 degrees and 136 degrees. The median tuning index, 44.5 degrees, corresponds to a full width at half maximum of 105 degrees. The ubiquity of selectivity for pursuit direction and the wide distribution of preferred directions indicates that pursuit direction uses a place-code type of representation in FEF; however, the broad directional tuning of most neurons suggests that pursuit direction is given by a weighted average of optimal directions across the population of pursuit neurons active at any given time. 4. In general, the responses of pursuit neurons increased with pursuit velocity. Of 13 neurons formally tested with 2 s of constant-velocity tracking in their preferred direction across a range of target speeds, pursuit velocity sensitivity ranged from 0.24 to 1.42 spikes.s-1.deg-1.s-1, with an average sensitivity of 0.70. This relationship suggests that pursuit neurons represent pursuit magnitude using a rate code; this parallels our previous observation that at most SEM sites, the velocity and acceleration of the electrically elicited eye movements increased as a function of the stimulation current.(ABSTRACT TRUNCATED AT 400 WORDS)

Frontal eye field activity preceding aurally guided saccades

1. We studied neuronal activity in the monkey's frontal eye field (FEF) in conjunction with saccades directed to auditory targets. 2. All FEF neurons with movement activity preceding saccades to visual targets also were active preceding saccades to auditory targets, even when such saccades were made in the dark. Movement cells generally had comparable bursts for aurally and visually guided saccades; visuomovement cells often had weaker bursts in conjunction with aurally guided saccades. 3. When these cells were tested from different initial fixation directions, movement fields associated with aurally guided saccades, like fields mapped with visual targets, were a function of saccade dimensions, and not the speaker's spatial location. Thus, even though sound location cues are chiefly craniotopic, the crucial factor for a FEF discharge before aurally guided saccades was the location of auditory target relative to the current direction of gaze. 4. Intracortical microstimulation at the sites of these cells evoked constant-vector saccades, and not goal-directed saccades. The direction and size of electrically elicited saccades generally matched the cell's movement field for aurally guided saccades. 5. Thus FEF activity appears to have a role in aurally guided as well as visually guided saccades. Moreover, visual and auditory target representations, although initially obtained in different coordinate systems, appear to converge to a common movement vector representation at the FEF stage of saccadic processing that is appropriate for transmittal to saccade-related burst neurons in the superior colliculus and pons.

Hydrocele of the canal of Nuck

The authors discuss hydrocele in the female processus vaginalis (hydrocele in the canal of Nuck) and present new case reports. The treatment of choice is surgical excision. The hydrocele is excised through a groin incision. The authors present four new cases.

The effect of cocaine on the physiologic response to hemorrhagic shock

BACKGROUND

Bradycardia is thought to be an uncommon and abnormal response to acute blood loss. A review of trauma patients (n = 84) admitted during a 1-year period with a systolic blood pressure of less than 100 mm Hg revealed that 45% had relative bradycardia (heart rate < 100 beats/minute). Cocaine use was recorded more often in this group (76% versus 26%; p < 0.05) compared with patients with tachycardia (heart rate > or = 100 beats/minute). We investigated the effect of cocaine use on the response to acute blood loss in an animal model of hemorrhagic shock.

METHODS

Rats were given intraperitoneal cocaine 20 mg/kg/day for 14 days (n = 10) or saline solution (n = 10). The rats were bled until 30% of their blood volume was shed; they were resuscitated 30 minutes later.

RESULTS

Cocaine-treated rats showed a decreased 24-hour survival rate (50% versus 100%; p < 0.05), a relative bradycardic response compared to baseline heart rate (-8.9% +/- 6.4% versus 7.5% +/- 3.5%; p < 0.05), and a greater drop in mean arterial blood pressure (-55.5% +/- 4.8% versus -37.0% +/- 5.5%; p < 0.05) by 5 minutes of shock. Cocaine-treated rats were more acidotic after shock compared to controls (pH 7.36 +/- 0.03 versus 7.44 +/- 0.02; p < 0.05).

CONCLUSIONS

Cocaine had a deleterious effect on experimental hemorrhage. The bradycardic response observed in our trauma patients may be due, in part, to cocaine abuse, and we postulate that chronic cocaine use alters the normal adrenergic response to blood loss.

Topography of projections to the frontal lobe from the macaque frontal eye fields

Efferents from the frontal eye fields (FEF) to the ipsilateral frontal lobe were studied by autoradiography of tritiated tracers (leucine, proline, and fucose) in seven macaque monkeys that were used previously to describe subcortical connections. In four of the cases, tracer injection sites were confirmed by low thresholds for the electrical elicitation of saccadic eye movements. Cases were grouped as lFEF of sFEF cases according to large or small saccades that were characteristic of the injection site. Projections from the FEF terminated in five frontal regions: 1) area FD on the dorsomedial convexity; 2) area FC (containing SEF) medial to the upper limb of the arcuate sulcus; 3) areas FD and FD delta along the walls of the principal sulcus; 4) area FCBm on the deep, posterior wall of the arcuate sulcus inferior to the sulcal spur; and 5) the inferolateral cortex (area FDi) on the convexity and lateral two thirds of the anterior wall of the arcuate sulcus. Projections in sFEF cases tended to be confined to medial parts of dorsomedial FD and FC and the lateral wall of the principal sulcus and inferolateral convexity. Neither lFEF nor sFEF appeared to project to the SMA or pericingulate cortex. Label in these areas was found only in the cases in which tracer spread into non-FEF areas. FEF projections terminated in column-like patches of about 500-600 microns in diameter. Labeled axons and terminals were seen in all cortical layers regardless of location in the frontal lobe.

Dorsolateral prefrontal lesions and oculomotor delayed-response performance: evidence for mnemonic "scotomas"

The spatial memory functions of the monkey's prefrontal cortex were examined with oculomotor delayed-response (ODR) paradigms that required the animal to remember the spatial location of peripheral visual cues, while maintaining fixation on a central visual target during the presentation of each cue and during a subsequent 1.5-8 sec delay period. Four rhesus monkeys received unilateral or serial prefrontal lesions in and around the principal sulcus after they reached criterion performance on the ODR tasks. Unilateral lesions disrupted the performance of memory-guided eye movements to spatial cues in the visual field contralateral to the hemisphere in which the lesion was placed. Memory-guided eye movements to ipsilateral cues were mildly affected by unilateral lesions, and these lesions had little or no effect on performance in visually guided control tasks. With addition of a second lesion in the opposite hemisphere, the deficit was extended to include the opposite hemifield. The impairment was characterized by eye movements of inappropriate direction, and, excepting the one lesion that extended into the frontal eye field region of the arcuate sulcus, saccadic reaction times and velocities were the same before and after the lesions. The effect of the lesions was delay dependent: performance was rarely altered at the shortest (1.5 sec) delay but became progressively worse as the delay period was lengthened. The present results strengthen the evidence that the delayed-response deficits of monkeys with prefrontal lesions are caused by failure to maintain a transient memory "trace" in working memory, and indicate for the first time that working memory mechanisms are lateralized: memories for visuo-spatial coordinates in each hemifield are processed primarily in the contralateral prefrontal cortex. These findings provide evidence for the concept of mnemonic hemianopias and mnemonic scotomas, that is, memory deficits for particular hemifields or visual field locations, unaccompanied by simple sensory or motor deficits.

Smooth eye movements elicited by microstimulation in the primate frontal eye field

1. We electrically stimulated the macaque monkey's frontal eye field (FEF) region to localize and to analyze the smooth pursuit eye movement representation. Rhesus monkeys were trained to fixate stationary spots of light, and trains of stimulation (usually 250-500 ms at 10-100 microA) were applied while the fixation targets remained lit and stationary. This paradigm was used in a total of 485 electrode penetrations through the arcuate sulcus region of six hemispheres in three adult monkeys. Smooth eye movements (SEMs), clearly distinct from saccades, were elicited at 86 sites in 53 of these penetrations. These SEMs had an average peak velocity of 11 degrees/s and an average latency of 39 ms. 2. The initial acceleration and peak velocity of elicited SEMs increased with stimulation intensity at any given site. On the other hand, SEM direction was characteristic of a given stimulation site and did not vary with stimulation intensity. These findings indicate that SEM amplitude is coded by the intensity of neural activity, and SEM direction is coded by the location of this activity within the cortex ("rate" vs. "place" codes). 3. SEMs elicited in the presence of a stationary fixation target (closed-loop conditions) typically reached a plateau velocity early in the stimulation and maintained that velocity throughout most of the stimulation train. However, when retinal slip was eliminated by artificially stabilizing the fixation target on the fovea (open-loop conditions), the electrical stimulation caused the eye to accelerate for longer periods and to attain higher velocities than in the closed-loop condition. Eye velocities obtained at the same site in open- and closed-loop conditions diverged from one another approximately 100 ms after SEM onset, consistent with the visual latency of the pursuit system. These findings suggest that the FEF primarily conveys an eye acceleration signal, rather than an eye velocity goal, to the pursuit system, and that this signal can be affected by visual retinal errors before effecting the smooth eye movements. 4. SEMs were elicited from a small portion of the arcuate fundus and neighboring posterior bank lying directly posterior to the principal sulcus. Functionally, this SEM region was surrounded by the saccadic FEF and by somatic premotor cortex. 5. Even though ipsilateral, contralateral, and vertical SEMs were elicited, the distribution of SEM directions was skewed toward ipsilateral movements. This tendency was more pronounced for sites in the arcuate fundus, whereas SEMs elicited from the posterior arcuate bank were often directed contralaterally and vertically.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of eye position within the orbit on electrically elicited saccadic eye movements: a comparison of the macaque monkey's frontal and supplementary eye fields

1. We quantitatively compared the effects of eye position within the orbit on saccadic eye movements electrically elicited from two oculomotor areas of the macaque monkey's frontal lobe cortex: the frontal eye field (FEF) and the supplementary eye field (SEF). 2. The effect of eye position on electrically elicited saccades was studied by delivering 70-ms trains of intracortical microstimulation while the monkeys fixated a spot of light. Tests of different fixation points located across a rectangular array were randomly intermixed. Complete experiments were carried out on 38 sites in three FEFs of two monkeys and 59 sites from three SEFs of the same two monkeys. Stimulation currents for the array experiments were usually 10-20 microA above the site threshold; the average current used was 36 microA for FEF and 49 microA for SEF. 3. The magnitude of effect of the initial eye position on the elicited saccade's dimensions was quantified at each site by computing the linear regression of saccadic eye movement displacement on the eye position within the orbit when stimulation was applied. This computation was done separately for the horizontal and vertical axes. We call the resulting pair of regression coefficients "orbital perturbation indexes." Indexes of 0.0 represent elicited saccades that do not change their trajectory with different initial eye positions (constant-vector saccades), whereas indexes of -1.0 represent elicited saccades that end at the same orbital position regardless of initial eye position (goal-directed saccades). 4. The effect of eye position varied across sites. In both FEF and SEF, the orbital perturbation indexes were distributed between approximately 0.0 and -0.5, with the horizontal and vertical indexes highly correlated across sites. 5. The average orbital perturbation indexes were small for both eye fields and were not significantly different. The mean horizontal indexes were -0.13 and -0.16 for SEF and FEF, respectively. The mean vertical indexes were -0.16 and -0.13. Neither SEF versus FEF difference was statistically significant. 6. In both SEF and FEF, sites yielding larger-amplitude saccades generally had larger orbital effects than sites yielding smaller saccades. This relationship accounted for the majority of the variability of the orbital perturbation indexes across sites in both SEF and FEF. 7. These results indicate that SEF and FEF are not distinguished from each other by the orbital dependence of their electrically elicited saccades. Thus they do not confirm the previously hypothesized dichotomy that FEF codes constant-vector saccades and SEF codes goal-directed saccades.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuronal activity related to saccadic eye movements in the monkey's dorsolateral prefrontal cortex

1. Single-neuron activity was recorded from the prefrontal cortex of monkeys performing saccadic eye movements in oculomotor delayed-response (ODR) and visually guided saccade (VGS) tasks. In the ODR task the monkey was required to maintain fixation of a central spot throughout the 0.5-s cue and 3.0-s delay before making a saccadic eye movement in the dark to one of four or eight locations where the visual cue had been presented. The same locations were used for targets in the VGS tasks; however, unlike the ODR task, saccades in the VGS tasks were visually guided. 2. Among 434 neurons recorded from prefrontal cortex within and surrounding the principal sulcus (PS), 147 changed their discharge rates in relation to saccadic eye movements in the ODR task. Their response latencies relative to saccade initiation were distributed between -192 and 460-ms, with 22% exhibiting presaccadic activity and 78% exhibiting only postsaccadic activity. Among PS neurons with presaccadic activity, 53% also had postsaccadic activity when the monkey made saccadic eye movements opposite to the directions for which the presaccadic activity was observed. 3. Almost all (97%) PS neurons with presaccadic activity were directionally selective. The best direction and tuning specificity of each neuron were estimated from parameters used to fit a Gaussian tuning curve function. The best direction for 62% of the neurons with presaccadic activity was toward the contralateral visual field, with the remaining neurons having best directions toward the ipsilateral field (23%) or along the vertical meridian (15%). 4. Most postsaccadic activity of PS neurons (92%) was also directionally selective. The best direction for 48% of these neurons was toward the contralateral visual field, with the remaining neurons having best directions toward the ipsilateral field (36%) or along the vertical meridian (16%). Eighteen percent of the neurons with postsaccadic activity showed a reciprocal response pattern: excitatory responses occurred for one set of saccade directions, whereas inhibitory responses occurred for roughly the opposite set of directions. 5. Sixty PS neurons with saccade-related activity in the ODR task were also examined in a VGS task. Forty of these neurons showed highly similar profiles of directional specificity and response magnitude in both tasks, 13 showed saccade-related activity only in the ODR task, and 7 changed their response characteristics between the ODR and VGS tasks.(ABSTRACT TRUNCATED AT 400 WORDS)

Smooth-pursuit eye movement representation in the primate frontal eye field

Physiological and behavioral data reported here show an involvement of the primate frontal eye field (FEF) cortex in smooth-pursuit eye movements, in addition to its well-established role in saccadic eye movements. Microstimulation just ventral to the small saccade representation of the FEF elicits eye movements that, in contrast to elicited saccades, have low velocities, continue smoothly without interruption during prolonged stimulation, and are usually directed ipsilaterally to the stimulated hemisphere. Neurons in this region respond in association with smooth-pursuit eye movements and visual motion. Tracking deficits following experimental lesions of the FEF depend critically upon the status of this ventral region: superficial lesions sparing it leave smooth-pursuit eye movements intact, whereas lesions removing it produce substantial deficits in the anticipatory initiation, motion-induced acceleration, asymptotic velocity, and predictive continuation of ipsilateral smooth pursuit.

Primate frontal eye fields. III. Maintenance of a spatially accurate saccade signal

1. We studied the activity of single neurons in the monkey frontal eye fields during oculomotor tasks designed to assess the activity of these neurons when there was a dissonance between the spatial location of a target and its position on the retina. 2. Neurons with presaccadic activity were first studied to determine their receptive or movement fields and to classify them as visual, visuomovement, or movement cells with the use of the criteria described previously (Bruce and Goldberg 1985). The neurons were then studied by the use of double-step tasks that dissociated the retinal coordinates of visual targets from the dimensions of saccadic eye movements necessary to acquire those targets. These tasks required that the monkeys make two successive saccades to follow two sequentially flashed targets. Because the second target disappeared before the first saccade occurred, the dimensions of the second saccade could not be based solely on the retinal coordinates of the target but also depended on the dimensions of the first saccade. We used two versions of the double-step task. In one version neither target appeared in the cell's receptive or movement field, but the second eye movement was the optimum amplitude and direction for the cell (right-EM/wrong-RF task). In the other the second stimulus appeared in the cell's receptive field, but neither eye movement was appropriate for the cell (wrong-EM/right-RF task). 3. Most frontal-eye-field cells discharged in the right-EM/wrong-RF version of the double-step task. Their discharge began after the first saccade and continued until the second saccade was made. They usually discharged even on occasional trials in which the monkey failed to make the second saccade. They discharged much less, or not at all, in the wrong-EM/right-RF version of the double-step paradigm. Thus most presaccadic cells in the frontal eye fields were tuned to the dimensions of saccadic eye movements rather than to the coordinates of retinal stimulation. 4. Eleven movement cells (including 1 which also had independent postsaccadic activity for saccades opposite its presaccadic movement field) were studied, and all had significant activity in the right-EM/wrong-RF task. 5. Almost all (28/32) visuomovement cells, including 12 with independent postsaccadic activity, discharged in the right-EM/wrong-RF task. None of the four that failed had independent postsaccadic activity. 6. The majority (26/40) of visual cells were responsive in the right-EM/wrong-RF task.(ABSTRACT TRUNCATED AT 400 WORDS)

Visuospatial coding in primate prefrontal neurons revealed by oculomotor paradigms

1. Visual responses and their relationship to delay-period activity were studied by recording single neuron activity from the prefrontal cortex of rhesus monkeys while they performed an oculomotor delayed-response (ODR) and a visual probe (VP) task. In the ODR task, the monkey was required to maintain fixation of a central spot of light throughout the cue (0.5 s) and delay (3 s) periods and then make a saccadic eye movement to one of four or eight locations where the visual cue had been presented. In the VP task, the same visual stimuli that were used in the ODR task were presented for 0.5 s, but no response was required. The VP task was thus employed to test the passive visual response and, by comparison with cue-elicited activity in the ODR task, to examine the degree of behavioral enhancement present in prefrontal visual activity. 2. Among 434 neurons recorded from the prefrontal cortex within and surrounding the principal sulcus (PS), 261 had task-related activity during at least one phase of the ODR task, and 74 of these had phasic visual responses to the onset of the visual cues with a median latency of 116 ms. The visual responses of 69 neurons were excitatory, and 5 neurons were inhibited. Five of the neurons with excitatory visual responses also responded transiently after the offset of the cue. 3. Visual responses were classified as directional for 71 PS neurons (96%) in that excitatory or inhibitory responses occurred only for location of cues in a restricted portion of the visual field. Only 3 PS neurons were omnidirectional, i.e., responded equivalently to cues in all locations tested. 4. The best direction and tuning specificity of all PS neurons with directional visual responses were estimated from parameters yielding the best fit to a Gaussian-shaped tuning function. The best direction for the majority (71%) of neurons was toward the visual field contralateral to the hemisphere where the neuron was located. The remaining neurons had their best directions in the ipsilateral field (18%) or along the vertical meridian (11%). 5. The specificity of directional tuning for PS visual responses was quite variable, ranging from neurons that responded only to one of the eight cue locations to neurons that responded to all eight, but in a clearly graded fashion. The standard deviation parameter of the Gaussian curve indexed the breadth of directional tuning of each neuron; its median value was 37 degrees.(ABSTRACT TRUNCATED AT 400 WORDS)

Resolution of metabolic columns by a double-label 2-DG technique: interdigitation and coincidence in visual cortical areas of the same monkey

A double-label modification of the 2-deoxyglucose (DG) technique uses both 3H-2-DG and 14C-2-DG and allows for metabolic activity engaged by 2 distinct experimental conditions to be dissociated throughout the brain of a single subject. In the present study, we used this double-label method to examine the relationship between metabolic columns subserving the 2 eyes in cortical visual areas V1 and V2. The left and right eye's ocular dominance columns were separately activated in the same monkey to demonstrate that the double-label 2-DG method can resolve metabolic differences at the level of the cortical column. In 2 monkeys, 14C-2-DG was injected first and one eye was occluded while the other eye was visually stimulated for 30 min. Then 3H-2-DG was injected, and the occluder was switched so that the alternate eye was stimulated with the same pattern for 30 min. Autoradiographs depicting the 2 labels separately were obtained by exploiting the differential sensitivity of X-ray film and Ultrofilm to 3H and 14C emissions and by applying a radioactivity-subtraction algorithm to pairs of digitized images of the same section (Friedman et al., 1987). Columnar regions of increased activity were evident throughout V1, excepting the representations of the optic disk and monocular crescent. Superimposition of the 3H and 14C images from the same sections demonstrated that columns of increased 3H label were interdigitated with columns of increased 14C label in V1. In contrast, bands of increased 3H-2-DG uptake in extrastriate area V2 were largely coincident with the bands of increased 14C-2-DG uptake. These results illustrate the value of the double-label 2-DG technique for studying fluctuations of metabolic activity under different experimental conditions in the same subject. In the present example, the demonstration that ocular dominance columns are interdigitated in V1, whereas metabolically active bands are coincident in V2, would not have been fully appreciated by comparing 2-DG labeling across separate animals.

Mnemonic coding of visual space in the monkey's dorsolateral prefrontal cortex

1. An oculomotor delayed-response task was used to examine the spatial memory functions of neurons in primate prefrontal cortex. Monkeys were trained to fixate a central spot during a brief presentation (0.5 s) of a peripheral cue and throughout a subsequent delay period (1-6 s), and then, upon the extinction of the fixation target, to make a saccadic eye movement to where the cue had been presented. Cues were usually presented in one of eight different locations separated by 45 degrees. This task thus requires monkeys to direct their gaze to the location of a remembered visual cue, controls the retinal coordinates of the visual cues, controls the monkey's oculomotor behavior during the delay period, and also allows precise measurement of the timing and direction of the relevant behavioral responses. 2. Recordings were obtained from 288 neurons in the prefrontal cortex within and surrounding the principal sulcus (PS) while monkeys performed this task. An additional 31 neurons in the frontal eye fields (FEF) region within and near the anterior bank of the arcuate sulcus were also studied. 3. Of the 288 PS neurons, 170 exhibited task-related activity during at least one phase of this task and, of these, 87 showed significant excitation or inhibition of activity during the delay period relative to activity during the intertrial interval. 4. Delay period activity was classified as directional for 79% of these 87 neurons in that significant responses only occurred following cues located over a certain range of visual field directions and were weak or absent for other cue directions. The remaining 21% were omnidirectional, i.e., showed comparable delay period activity for all visual field locations tested. Directional preferences, or lack thereof, were maintained across different delay intervals (1-6 s). 5. For 50 of the 87 PS neurons, activity during the delay period was significantly elevated above the neuron's spontaneous rate for at least one cue location; for the remaining 37 neurons only inhibitory delay period activity was seen. Nearly all (92%) neurons with excitatory delay period activity were directional and few (8%) were omnidirectional. Most (62%) neurons with purely inhibitory delay period activity were directional, but a substantial minority (38%) was omnidirectional. 6. Fifteen of the neurons with excitatory directional delay period activity also had significant inhibitory delay period activity for other cue directions. These inhibitory responses were usually strongest for, or centered about, cue directions roughly opposite those optimal for excitatory responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Frontal eye field efferents in the macaque monkey: I. Subcortical pathways and topography of striatal and thalamic terminal fields

Anterograde tracers (tritiated leucine, proline, fucose; WGA-HRP) were injected into sites within the frontal eye fields (FEF) of nine macaque monkeys. Low thresholds (less than or equal to 50 microA) for electrically evoking saccadic eye movements were used to locate injection sites in four monkeys. Cases were grouped according to the amplitude of saccades evoked or predicted at the injection site. Dorsomedial prearcuate injection sites where large saccades were elicited were classified as lFEF cases, whereas ventrolateral prearcuate sites where small saccades were evoked were designated sFEF cases. One control case was injected in the medial postarcuate area 6. We found five descending fiber bundles from FEF; fibers to the striatum, which enter the caudate nucleus at or just rostral to the genu of the internal capsule; fibers to the claustrum, which travel in the external capsule; and transthalamic, subthalamic, and pedunculopontine fibers. Our results indicate that transthalamic and subthalamic pathways supply all terminal sites in the thalamus, subthalamus, and tegmentum of the midbrain and pons, whereas pedunculopontine fibers appear to terminate in the pontine and reticularis tegmenti pontis nucleus exclusively. Frontal eye field terminal fields in the striatum were topographically organized: lFEF projections terminated dorsal and rostral to sFEF projections. Thus, lFEF terminal fields were located centrally in the head and body of the caudate nucleus and a small dorsomedial portion of the putamen, whereas sFEF terminal fields were located in ventrolateral parts of the caudate body and ventromedial parts of the putamen. In the claustrum, lFEF projections terminated dorsal and rostral to sFEF projections. Projections from FEF terminated in ventral and caudal parts of the subthalamic nucleus without a clear topography. By comparison, terminal fields from medial postarcuate area 6 were located more caudally and laterally in the striatum and claustrum than projections from FEF, and more centrally in the subthalamic nucleus. In the thalamus, FEF terminal patches in some thalamic nuclei were also topographically organized. Projections from lFEF terminated in dorsal area X, dorsolateral medial dorsal nucleus, pars parvicellularis (MDpc), and the caudal pole of MDpc, whereas projections from sFEF terminated in ventral area X, medial dorsal nucleus, pars multiformis, and caudal medial dorsal nucleus pars densocellularis.(ABSTRACT TRUNCATED AT 400 WORDS)

Frontal eye field efferents in the macaque monkey: II. Topography of terminal fields in midbrain and pons

Frontal eye field (FEF) projections to the midbrain and pons were studied in nine macaque monkeys that were used to study FEF projections to the striatum and thalamus (Stanton et al.: J. Comp. Neurol. 271:473-492, '88). Injections of tritiated amino acids or WGA-HRP were made into FEF cortical locations where low-level microstimulation (less than or equal to 50 microA) elicited saccadic eye movements, and anterograde axonal labeling was mapped. The injections were made into the anterior bank of the arcuate sulcus from dorsomedial sites where large saccades were evoked (lFEF) to ventrolateral sites where small saccades were evoked (sFEF). The largest terminal fields of FEF fibers were located in the ipsilateral superior colliculus (SC). Projections to SC were topographically organized: lFEF sites projected to intermediate and deep layers of caudal SC, sFEF sites projected to intermediate and superficial layers of rostral SC, and FEF sites between these extremes projected to intermediate locations in SC. Patches of terminal labeling were located ipsilaterally in the lateral mesencephalic reticular formation near the parabigeminal nucleus and the ventrolateral pontine reticular formation. These patches were larger from lFEF injections. Small, dense terminal patches were seen in the ipsilateral pontine gray, mostly along the medial and dorsal borders of these nuclei but occasionally in central and dorsolateral regions. Patches of label like those in the pontine nuclei were located ipsilaterally in the reticularis tegmenti pontis nucleus in lFEF cases and bilaterally in sFEF cases. Small terminal patches were found in the nucleus of Darkschewitsch and dorsal and medial parts of the parvicellular red nucleus in most FEF cases. In the pretectal region, labeled terminal patches were consistently found in the nucleus limitans of the posterior thalamus, but we could not determine if label in the nucleus of the pretectal area and dorsal parts of the nucleus of the posterior commissure marked axon terminals or fibers of passage. We found small, lightly labeled terminal patches in the pontine raphe between the rootlets of the abducens nerve (three cases) or in the adjacent paramedian pontine reticular formation (one case). Omnipauser cells in this region are important in initiating saccades. In one sFEF case, very small patches of label were located in the supragenual nuclei anterior to the abducens nuclei and in the ipsilateral nucleus prepositus hypoglossi posterior to the abducens nucleus. Presaccadic burster neurons in the periabducens region are known to fire immediately before horizontal saccades.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of striate cortex in the guidance of eye movements in the monkey

We studied the effect of unilateral striate cortical ablations on smooth pursuit and saccadic eye movements in the monkey. The monkeys made quite accurate saccades to stationary stimuli in the field contralateral to the lesion, and they readily pursued foveal targets moving in all directions. However, when visual stimuli were stepped into the field contralateral to the lesion and then began to move, thus insuring that the moving stimulus was confined to the impaired visual hemifield, several oculomotor abnormalities emerged. Saccades to moving stimuli presented in the impaired field consistently undershot targets that moved away from the central fixation point after the step, and overshot targets that moved back towards the central fixation point. There was little or no smooth pursuit eye velocity generated in any direction to moving stimuli in the impaired field, and the monkeys could not generate smooth pursuit to stimuli maintained a few degrees from the fovea in the impaired field, although they were able to pursue such stimuli held in the normal field. Ablation of striate cortex also affected the latencies of saccades. When step-ramp stimuli were presented in the normal field, the monkeys delayed the initiation of saccades to targets moving towards the central fixation point, and hastened the initiation of saccades to targets moving away from the central fixation point. By contrast, changes in the direction of target movement did not affect the latencies of saccades into the impaired field. The deficits seemed permanent, lasting as long as the monkeys were tested--over 2 years in one case--but they were not total. Each monkey could use stimuli moving into the affected field to develop some eye velocity, although this residual ability had a much longer latency and lower gain than that provided by the intact visual system. These results show that striate cortex is intimately involved in the estimation of stimulus velocity critical to the genesis of smooth pursuit and saccadic eye movements.

A sequential double-label 14C- and 3H-2-DG technique: validation by double-dissociation of functional states

We investigated a double-label 2-DG protocol and method of analysis in which sequential injections of 3H- and 14C-2-DG were used to map brain metabolism during two distinct experimental treatments in the same animal. In initial studies, brain sections from rats given only 3H-2-DG or only 14C-2-DG were exposed on Ultrofilm and on X-ray film with an interposed sheet of mylar (X-ray/mylar). These studies were needed to determine whether, at the 50:1 3H:14C dose ratio used, 3H-2-DG uptake would be revealed only in Ultrofilm images and 14C-2-DG uptake only in X-ray/mylar images. We found that X-ray/mylar images indeed showed only 14C-2-DG uptake as 3H emissions were blocked by the protective coating of the film and the mylar. By contrast, Ultrofilm autoradiograms showed the 2-DG uptake pattern for both the 14C-2-DG and 3H-2-DG cases. We then examined autoradiograms from double-label cases in which 14C-2-DG and 3H-2-DG were sequentially given using a 100:1 3H:14C dose ratio, with a different treatment following each injection. As predicted from the single-label cases, activity in the X-ray/mylar images corresponded to the treatment that followed the 14C-2-DG injection, while the Ultrofilm images reflected both treatments and thus were not veridical representations of 3H label. This paper provides a solution to the contamination of Ultrofilm by 14C label in that we devised a subtraction algorithm using a computerized imaging system which removes the contaminating 14C from the Ultrofilm image, leaving a 'Difference' image of 3H-2-DG uptake. Difference images revealed activity consistent with the treatment that followed the 3H-2-DG injection. Thus, the X-ray/mylar and difference images separately indexed metabolic activity for two different functional states in the same subject. By allowing a subject to serve as its own control, this double-label method greatly increases the applicability and power of the 2-DG method.

Both striate cortex and superior colliculus contribute to visual properties of neurons in superior temporal polysensory area of macaque monkey

Although the tectofugal system projects to the primate cerebral cortex by way of the pulvinar, previous studies have failed to find any physiological evidence that the superior colliculus influences visual activity in the cortex. We studied the relative contributions of the tectofugal and geniculostriate systems to the visual properties of neurons in the superior temporal polysensory area (STP) by comparing the effects of unilateral removal of striate cortex, the superior colliculus, or of both structures. In the intact monkey, STP neurons have large, bilateral receptive fields. Complete unilateral removal of striate cortex did not eliminate visual responses of STP neurons in the contralateral visual hemifield; rather, nearly half the cells still responded to visual stimuli in the hemifield contralateral to the lesion. Thus the visual properties of STP neurons are not completely dependent on the geniculostriate system. Unilateral striate lesions did affect the response properties of STP neurons in three ways. Whereas most STP neurons in the intact monkey respond similarly to stimuli in the two visual hemifields, responses to stimuli in the hemifield contralateral to the striate lesion were usually weaker than responses in the ipsilateral hemifield. Whereas the responses of many STP neurons in the intact monkey were selective for the direction of stimulus motion or for stimulus form, responses in the hemifield contralateral to the striate lesion were not selective for either motion or form. Whereas the median receptive field in the intact monkey extended 80 degrees into the contralateral visual field, the receptive fields of cells with responses in the contralateral field that survived the striate lesions had a median border that extended only 50 degrees into the contralateral visual field. Removal of both striate cortex and the superior colliculus in the same hemisphere abolished the responses of STP neurons to visual stimuli in the hemifield contralateral to the combined lesion. Nearly 80% of the cells still responded to visual stimuli in the hemifield ipsilateral to the lesion. Unilateral removal of the superior colliculus alone had only small effects on visual responses in STP. Receptive-field size and visual response strength were slightly reduced in the hemifield contralateral to the collicular lesion. As in the intact monkey, selectivity for stimulus motion or form were similar in the two visual hemifields. We conclude that both striate cortex and the superior colliculus contribute to the visual responses of STP neurons. Striate cortex is crucial for the movement and stimulus specificity of neurons in STP.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of attentive fixation on eye movements evoked by electrical stimulation of the frontal eye fields

Electrical stimulation of the frontal eye fields of the rhesus monkey evokes saccadic eye movements. Both the amplitude of electrically elicited saccades and the threshold current for eliciting them are primarily determined by the location of the stimulating electrode within the frontal eye fields; however, threshold and amplitude also are systematically affected by the monkey's behavioral state when the stimulation is applied. If the monkey is alert, but not performing a task, saccade amplitudes are largest and thresholds are lowest. Conversely, if the monkey actively fixates a visual target, elicited saccades are smaller and threshold currents are higher. Saccades evoked during fixation have slower velocities appropriate for their reduced amplitude. Phase plane plots of eye velocity versus eye position indicate that these saccades are originally programmed to be smaller and slower, and hence are not large saccades voluntarily braked in mid-flight. As opposed to their amplitude and threshold, the direction of electrically evoked saccades is unaffected by the state of fixation. The state of attentive fixation, but not the visual fixation target itself, is the responsible factor for these effects. These results suggest that there is a difference between the state of active fixation and the state of having the eye still in the orbit without active fixation. The oculomotor system in the latter case is relatively more susceptible to signals from the cerebral cortex.