Physiological changes in the pallidum in a progressive model of Parkinson's disease: Are oscillations enough?

Neurophysiological changes in the basal ganglia thalamo-cortical circuit associated with the development of parkinsonian motor signs remain poorly understood. Theoretical models have ranged from those emphasizing changes in mean discharge rate to increased oscillatory activity within the beta range. The present study characterized neuronal activity within and across the internal and external segments of the globus pallidus as a function of motor severity using a staged, progressively severe 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinsonism in three rhesus monkeys. An increase in coherence between neuronal pairs across the external and internal globus pallidus was present in multiple frequency bands in the parkinsonian state; both the peak frequency of oscillatory coherence and the variability were reduced in the parkinsonian state. The incidence of 8-20Hz oscillatory activity in the internal globus pallidus increased with the progression of the disease when pooling the data across the three animals; however it did not correlate with motor severity when assessed individually and increased progressively in only one of three animals. No systematic relationship between mean discharge rates or the incidence or structure of bursting activity and motor severity was observed. These data suggest that exaggerated coupling across pallidal segments contribute to the development of the parkinsonian state by inducing an exaggerated level of synchrony and loss of focusing within the basal ganglia. These data further point to the lack of a defined relationship between rate changes, the mere presence of oscillatory activity in the beta range and bursting activity in the basal ganglia to the motor signs of Parkinson's disease.

Thalamic post-inhibitory bursting occurs in patients with organic dystonia more often than controls

We now test the hypothesis that post-inhibitory bursting in the human pallidal receiving nucleus of the thalamus (ventral oral) mediates inhibitory pallido-thalamic transmission during dystonia. We have compared thalamic single neuron activity in nine patients with organic dystonia to that in a patient with psychogenic dystonia (Psyd) and in healthy waking monkeys. In organic dystonia, EMG power is commonly concentrated at the lowest frequency of the smoothed autopower spectrum (0.39Hz). Therefore, segments of spike trains with a signal-to-noise ratio ≥2 at 0.39Hz were termed dystonia frequency (DF) segments, which occurred more commonly during dystonia related to movement. Those with a SNR<2 were termed non-dystonia frequency (nDF) segments, which were associated with spontaneous dystonia. We concentrated on nDF activity since neuronal activity in our controls was measured at rest. Neuronal spike trains were categorized into those with post-inhibitory bursts (G, grouped), with single spikes (NG, non-grouped), or with both single spikes and bursts (I, intermediate). nDF spike trains in ventral oral had more G category firing in dystonia than in controls. The burst rate and the pre-burst silent period in nDF firing of organic dystonia were consistently greater than those of both the monkeys and the patient with Psyd. The distribution of the pre-burst silent period was bimodal with a longer mode of approximately GABAb (gamma amino butyric acid receptor-type b) duration. These results demonstrate distinct differences of post-inhibitory bursting in organic dystonia versus controls. The presence of inhibitory events consistent with GABAb duration suggests interventions for treatment of dystonia.

Deep brain stimulation activation volumes and their association with neurophysiological mapping and therapeutic outcomes

OBJECTIVE

Despite the clinical success of deep brain stimulation (DBS) for the treatment of Parkinson's disease (PD), little is known about the electrical spread of the stimulation. The primary goal of this study was to integrate neuroimaging, neurophysiology and neurostimulation data sets from 10 patients with PD, unilaterally implanted with subthalamic nucleus (STN) DBS electrodes, to identify the theoretical volume of tissue activated (VTA) by clinically defined therapeutic stimulation parameters.

METHODS

Each patient specific model was created with a series of five steps: (1) definition of the neurosurgical stereotactic coordinate system within the context of preoperative imaging data; (2) entry of intraoperative microelectrode recording locations from neurophysiologically defined thalamic, subthalamic and substantia nigra neurons into the context of the imaging data; (3) fitting a three dimensional brain atlas to the neuroanatomy and neurophysiology of the patient; (4) positioning the DBS electrode in the documented stereotactic location, verified by postoperative imaging data; and (5) calculation of the VTA using a diffusion tensor based finite element neurostimulation model.

RESULTS

The patient specific models show that therapeutic benefit was achieved with direct stimulation of a wide range of anatomical structures in the subthalamic region. Interestingly, of the five patients exhibiting a greater than 40% improvement in their Unified PD Rating Scale (UPDRS), all but one had the majority of their VTA outside the atlas defined borders of the STN. Furthermore, of the five patients with less than 40% UPDRS improvement, all but one had the majority of their VTA inside the STN.

CONCLUSIONS

Our results are consistent with previous studies suggesting that therapeutic benefit is associated with electrode contacts near the dorsal border of the STN, and provide quantitative estimates of the electrical spread of the stimulation in a clinically relevant context.

The persistent effects of unilateral pallidal and subthalamic deep brain stimulation on force control in advanced Parkinson's patients

The persistent effects of unilateral deep brain stimulation (DBS) of the globus pallidus interna (GPi) or subthalamic nucleus (STN) on specific movement parameters produced by Parkinson's disease (PD) patients are poorly understood. The aim of this study was to determine the effects of unilateral GPi and STN DBS on the force-producing capabilities of PD patients during maximal efforts and functional bimanual dexterity. Clinical and biomechanical data were collected from 14 unilaterally implanted patients (GPi=7; STN=7), at least 13 months post-DBS surgery, during On and Off stimulation in the absence of medication. Unilateral DBS of either location produced a 33% improvement in UPDRS motor scores. Significant gains in maximum force production were present in both limbs during unimanual efforts. The greatest increase in maximum force, for both limbs, was under bimanual conditions. Force in the contralateral limb increased more than 30% during bimanual efforts while ipsilateral force increased by 25%. Unilateral DBS improved grasping force control and consistency of digit placement during the performance of a bimanual dexterity task. The clinical and biomechanical data indicate that unilateral DBS of GPi or STN results in persistent improvements in the control and coordination of grasping forces during maximal efforts and functional dexterous actions. Unilateral DBS implantation of either site should be considered an option for those patients in which bilateral procedures are contraindicated.

Pseudobulbar crying induced by stimulation in the region of the subthalamic nucleus

We describe a case of pseudobulbar crying associated with deep brain stimulation (DBS) in the region of the subthalamic nucleus (STN). Patients with pseudobulbar crying show no other evidence of subjective feelings of depression such as dysphoria, anhedonia, or vegetative signs. This may be accompanied by other symptoms of pseudobulbar palsy and has been reported to occur with ischaemic or structural lesions in both cortical and subcortical regions of the brain. Although depression has been observed to result from DBS in the region of the STN, pseudobulbar crying has not been reported. A single patient who reported the symptoms of pseudobulbar crying after placement of an STN DBS was tested in the off DBS and on DBS conditions. The patient was tested using all four DBS lead contacts and the observations and results of the examiners were recorded. The Geriatric Depression Scale was used to evaluate for depression in all of the conditions. The patient exhibited pseudobulbar crying when on monopolar stimulation at all four lead contacts. The pseudobulbar crying resolved off stimulation. This case describes another type of affective change that may be associated with stimulation in the region of or within the STN. Clinicians should be aware of this potential complication, the importance of differentiating it from stimulation induced depression, and its response to a serotonin reuptake inhibitor, such as sertraline.

Mood changes with deep brain stimulation of STN and GPi: results of a pilot study

The results of this study suggest that there are mood changes associated with deep brain stimulation of the subthalamic nucleus (STN) and the globus pallidus interna (GPi). Further, optimal placement of electrodes in both STN and GPi seems to result in overall improvement in mood and is associated with a lower incidence of adverse mood effects than stimulation outside the optimal site. Preliminary data from this study, however, suggest that slight movement dorsal or ventral to the site of optimal motor performance may be associated with more adverse changes in mood with STN stimulation than with GPi stimulation.

Cognitive impairments in advanced PD without dementia

OBJECTIVE

To determine the nature and frequency of cognitive impairments in nondemented patients with advanced PD and their relationship to other variables potentially predictive of neuropsychological performance.

METHODS

The neuropsychological performance of nondemented, nondepressed patients with idiopathic PD (n = 61) was quantified with respect to clinically available normative data. The relationship of neuropsychological measures to motor symptoms, age, years of education, disease duration, age at disease onset, disease deterioration rate, and dopaminergic therapy was assessed.

RESULTS

Impairment was most frequent on measures sensitive to frontal lobe function (67% on Wisconsin Card Sorting Test number of categories, 30% on letter fluency, 30% on verbal learning). Poorer performance on multiple neuropsychological measures was related to greater overall motor abnormality (total Unified Parkinson's Disease Rating Scale score), increased bradykinesia on medication, older age, longer disease duration, and reduced education.

CONCLUSIONS

Even in the absence of dementia or depression, patients with advanced PD are likely to show clinically significant impairments on neuropsychological measures sensitive to changes in dorsolateral prefrontal regions participating in cognitive basal ganglia-thalamocortical circuits.

Neuropsychological and psychiatric sequelae of pallidotomy for PD: clinical trial findings

OBJECTIVE

To evaluate the neuropsychological and psychiatric sequelae of unilateral posterior pallidotomy for treatment of PD.

METHODS

Patients with idiopathic PD completed baseline and 3- and 6-month assessments after random assignment to an immediate surgery (n = 17) or medical management (n = 16) group.

RESULTS

Compared with the medical management group, the immediate surgery group with single lesions centered on the posterior internal pallidum showed superior naming and response inhibition, better verbal recall at 6 months, but greater distractibility, a tendency toward lower phonemic fluency, and a transient (3 months' only) semantic fluency deficit. The group with left lesions had more neuropsychological deficits than the group with right lesions or the medical management group, although these occurred mainly at 3 (but not 6) months. At 6 months, the patients with left lesions showed better verbal memory retention than the patients with right lesions. On most measures, the pattern of individual clinical change did not differ as a function of surgery or lesion laterality, with the exception of a higher frequency of decline in phonemic fluency in the patients with left lesions at 6 months. Although psychiatric status did not change overall, a history of depression tended to increase the risk of a depressive episode following surgery.

CONCLUSIONS

Well-targeted, uncomplicated, unilateral pallidotomy does not produce overall neuropsychological or psychiatric change, although there are subtle changes on specific measures sensitive to frontal lobe function.

Complications of gamma knife surgery for Parkinson disease

BACKGROUND

Many medical centers throughout the world offer radiosurgery with the gamma knife (GK) for pallidotomy and thalamotomy as a safe and effective alternative to radiofrequency ablative surgery and deep brain stimulation for Parkinson disease (PD). The reported incidence of significant complications varies considerably, and the long-term complication rate remains unknown.

DESIGN

We describe 8 patients seen during an 8-month period referred for complications of GK surgery for PD.

RESULTS

Of the 8 patients, 1 died as a result of complications, including dysphagia and aspiration pneumonia. Other complications included hemiplegia, homonymous visual field deficit, hand weakness, dysarthria, hypophonia, aphasia, arm and face numbness, and pseudobulbar laughter. In all patients, lesions were significantly off target.

CONCLUSIONS

The 8 patients with PD seen in referral at our center for complications of GK surgery highlight a spectrum of potential problems associated with this procedure. These include lesion accuracy and size and the delayed development of neurological complications secondary to radiation necrosis. Gamma knife surgery may have a higher complication rate than has been previously appreciated due to delayed onset and underreporting. We believe that the risk-benefit ratio of the GK will require further scrutiny when considering pallidotomy or thalamotomy in patients with PD. Physicians using this technique should carefully follow up patients postoperatively for delayed complications, and fully inform patients of these potential risks.

Physiology of hypokinetic and hyperkinetic movement disorders: model for dyskinesia

Although the basal ganglia have been implicated in the development of movement disorders since the 1940s, the exact role played by these structures has remained elusive. The development of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-monkey model of parkinsonism, and the recent resurgence of surgical therapy for the treatment of hypokinetic and hyperkinetic movement disorders has, however, led to an improved understanding of the pathophysiological mechanisms that underlie their development. In this article, we review the functional organization and examine the changes in neuronal activity that occur in the basal ganglia thalamocortical 'motor' circuit in these disorders. An alternative to the classic 'rate' model for Parkinson's disease is presented that incorporates the observed changes in neuronal activity, as well as additional neuronal pathways that contribute to these changes. Based on studies in animal models and humans with hyperkinetic movement disorders, it is postulated that dyskinesias develop as the result of a combination of excessive reductions in the mean discharge rate, altered patterns and increased synchronization of neurons in the internal segment of the globus pallidus. It is further postulated that the particular type of involuntary movement which develops also depends on the relative change in neuronal activity in the direct, indirect and alternative pathways. Support for these postulates is examined, and models for drug-induced dyskinesia, hemiballismus and dystonia are proposed.

Treatment of advanced Parkinson's disease by unilateral posterior GPi pallidotomy: 4-year results of a pilot study

To assess the long-term outcome following unilateral pallidotomy for advanced Parkinson's disease, we performed nonblinded Core Assessment Program for Intracerebral Transplantations protocol assessments in 10 of the original 15 patients in our pilot study for 4 years following surgery. Although Unified Parkinson's Disease Rating Scale motor examination scores returned to baseline levels at 3 and 4 years, most patients continued to show sustained improvements in contralateral tremor, akinesia, and drug-induced dyskinesias. Contralateral tremor was absent at 4 years in all seven patients with preoperative tremor. Contralateral "off" arm movement times (averaged for three tasks) decreased by 37% at 1 year and by 30% at 4 years. Contralateral dyskinesia scores improved by 82% at 1 year and by 64% at 4 years. In contrast, after reaching speeds equal to the contralateral side at 1 year, ipsilateral "off" movement times increased by 13% over baseline levels at 4 years. Although most gait and postural stability measures showed modest initial improvement followed by a return to baseline values, "on" stand-walk-sit task performance declined significantly at 4 years. Despite the restriction of our surgeries to one side and the expected natural progression of Parkinson's disease, the results of patient self-assessments suggest that 4 years after unilateral pallidotomy, most patients continue to experience a quality of life above preoperative levels.

Thalamic single neuron activity in patients with dystonia: dystonia-related activity and somatic sensory reorganization

Indirect evidence suggests that the thalamus contributes to abnormal movements occurring in patients with dystonia (dystonia patients). The present study tested the hypothesis that thalamic activity contributes to the dystonic movements that occur in such patients. During these movements, spectral analysis of electromyographic (EMG) signals in flexor and extensor muscles of the wrist and elbow exhibited peak EMG power in the lowest frequency band [0-0.78 Hz (mean: 0.39 Hz) dystonia frequency] for 60-85% of epochs studied during a pointing task. Normal controls showed low-frequency peaks for <16% of epochs during pointing. Among dystonia patients, simultaneous contraction of antagonistic muscles (cocontraction) at dystonia frequency during pointing was observed for muscles acting about the wrist (63% of epochs) and elbow (39%), but cocontraction was not observed among normal controls during pointing. Thalamic neuronal signals were recorded during thalamotomy for treatment of dystonia and were compared with those of control patients without motor abnormality who were undergoing thalamic procedures for treatment of chronic pain. Presumed nuclear boundaries of a human thalamic cerebellar relay nucleus (ventral intermediate, Vim) and a pallidal relay nucleus (ventral oral posterior, Vop) were estimated by aligning the anterior border of the principal sensory nucleus (ventral caudal, Vc) with the region where the majority of cells have cutaneous receptive fields (RFs). The ratio of power at dystonia frequency to average spectral power was >2 (P < 0.001) for cells in presumed Vop often for dystonia patients (81%) but never for control patients. The percentage of such cells in presumed Vim of dystonia patients (32%) was not significantly different from that of controls (31%). Many cells in presumed Vop exhibited dystonia frequency activity that was correlated with and phase-advanced on EMG activity during dystonia, suggesting that this activity was related to dystonia. Thalamic somatic sensory activity also differed between dystonia patients and controls. The percentage of cells responding to passive joint movement or to manipulation of subcutaneous structures (deep sensory cells) in presumed Vim was significantly greater in patients with dystonia than in control patients undergoing surgery for treatment of pain or tremor. Dystonia patients had a significantly higher proportion of deep sensory cells responding to movement of more than one joint (26%, 13/52) than did "control" patients (8%, 4/49). Deep sensory cells in patients with dystonia were located in thalamic maps that demonstrated increased representations of parts of the body affected by dystonia. Thus dystonia patients showed increased receptive fields and an increased thalamic representation of dystonic body parts. The motor activity of an individual sensory cell was related to the sensory activity of that cell by identification of the muscle apparently involved in the cell's receptive field. Specifically, we defined the effector muscle as the muscle that, by contraction, produced the joint movement associated with a thalamic neuronal sensory discharge, when the examiner passively moved the joint. Spike X EMG correlation functions during dystonia indicated that thalamic cellular activity less often was related to EMG in effector muscles (52%) than in other muscles (86%). Thus there is a mismatch between the effector muscle for a thalamic cell and the muscles with EMG correlated with activity of that cell during dystonia. This mismatch may result from the reorganization of sensory maps and may contribute to the simultaneous activation of multiple muscles observed in dystonia. Microstimulation in presumed Vim in dystonia patients produced simultaneous contraction of multiple forearm muscles, similar to the simultaneous muscle contractions observed in dystonia. (ABSTRACT TRUNCATED)

Neuronal activity in the basal ganglia in patients with generalized dystonia and hemiballismus

Microelectrode recording was performed in the basal ganglia of 3 patients with generalized dystonia and 1 patient with hemiballismus secondary to a brainstem hemorrhage. Neuronal activity was recorded from the internal and external segments of the globus pallidus and assessed for mean discharge rate and pattern of spontaneous activity. The responses of neurons in the internal segment of the globus pallidus to passive and active movements were also evaluated. Mean discharge rates of neurons in both segments of the pallidum in patients with dystonia and the patient with hemiballismus were considerably lower than those reported for patients with idiopathic Parkinson's disease. In addition, the pattern of spontaneous neuronal activity was highly irregular, occurring in intermittent grouped discharges separated by periods of pauses. Although receptive fields in the dystonia patients were widened and less specific than those reported in normal monkeys, neuronal responses to movement were uncommon in the hemiballismus patient. Before surgery, patients with dystonia experienced abnormal posturing and involuntary movements. Coactivation of agonist-antagonist muscle groups was observed both at rest and during the performance of simple movements. After pallidotomy there was a significant reduction in the involuntary movement associated with these disorders and a more normal pattern of electromyographic activity during rest and movement. Given the improvement in dystonic and hemiballistic movements in these patients after ablation of the sensorimotor portion of the internal segment of the globus pallidus, we suggest that pallidotomy can be an effective treatment for patients with dystonia and also for patients with medically intractable hemiballismus. Based on the finding of decreased neuronal discharge rates in pallidal neurons, we propose that physiologically dystonia most closely resembles a hyperkinetic movement disorder. A model for dystonia is proposed that incorporates the observed changes in the rate and pattern of neuronal activity in the pallidum with data from neuroimaging with positron emission tomography and 2-deoxyglucose studies.

Posterior ventral pallidotomy: techniques and theoretical considerations

1. Microeletrode mapping of the pallidum and adjacent structures allows for precise target identification and localization of critical structures, i.e., optic tract, internal capsule, and external pallidum, which must be spared from lesioning. 2. Microelectrode mapping has provided physiologic-anatomic correlation of determining the optimal target location as related to clinical outcome and has helped to refine the role of stimulation as a tool for target localization. 3. The improved accuracy of this technique should result in more accurate lesion placement which should improve long-term outcome and decrease morbidity.

Magnetic resonance imaging-based stereotactic localization of the globus pallidus and subthalamic nucleus

OBJECTIVE

To optimize the accuracy of initial stereotactic targeting for movement disorders surgery, we performed stereotactic localization of the internal segment of the globus pallidus (GPi) and subthalamic nucleus (STN) using magnetic resonance imaging protocols in which the borders of these nuclei were directly visualized.

METHODS

Fifty-one consecutive cases using the pallidal target and six using the subthalamic target were studied. Localization of these nuclei was performed using the Leksell stereotactic head frame and inversion recovery sequences (GPi) or T2-weighted spin echo sequences (STN). Targeting accuracy and individual variation in the spatial coordinates of these structures were independently measured by identification of nuclear boundaries during multiple microelectrode penetrations.

RESULTS

The lateral and vertical coordinates of an atlas-defined point in the GPi, with respect to the line between the anterior and posterior commissures, was highly variable. Initial targeting the GPi based on direct visualization of the target boundaries (external medullary lamina and optic tract) resulted in greater precision than would be expected using fixed anterior and posterior commissure-based coordinates. Initial targeting the STN using magnetic resonance imaging was sufficiently precise to place the initial microelectrode penetration within STN in all six cases.

CONCLUSION

Magnetic resonance imaging-based initial stereotactic targeting of the GPi, based on direct visualization of the target boundaries, is useful to improve target accuracy over that of purely indirect anterior and posterior commissure-based targeting methods. Initial targeting of the STN was reliably accomplished by direct visualization. However, there remains sufficient variability that the final target location in both GPi and STN required electrophysiological mapping in all cases.

Ablative surgery and deep brain stimulation for Parkinson's disease

Surgical options for Parkinson's disease (PD) are rapidly expanding and include ablative procedures, deep brain stimulation, and cell transplantation. The target nuclei for ablative surgery and deep brain stimulation are the motor thalamus, the globus pallidus, and the subthalamic nucleus. Multiple factors have led to the resurgence of interest in the surgical treatment of PD: 1) recognition that long-term medical therapy for PD is often unsatisfactory, with patients eventually suffering from drug-induced dyskinesias, motor fluctuations, and variable responses to medication; 2) greater understanding of the pathophysiology of PD, providing a better scientific rationale for some previously developed procedures and suggesting new targets; and 3) use of improved techniques, such as computed tomography- and magnetic resonance imaging-guided stereotaxy and single-unit microelectrode recording, making surgical intervention in the basal ganglia more precise. We review the present status of ablative surgery and deep brain stimulation for PD, including theoretical aspects, surgical techniques, and clinical results.

Microelectrode-guided pallidotomy: technical approach and its application in medically intractable Parkinson's disease

OBJECT

The authors describe the microelectrode recording and stimulation techniques used for localizing the caudal sensorimotor portion of the globus pallidus internus (GPi) and nearby structures (internal capsule and optic tract) in patients undergoing GPi pallidotomy.

METHODS

Localization is achieved by developing a topographic map of the abovementioned structures based on the physiological characteristics of neurons in the basal ganglia and the microexcitable properties of the internal capsule and optic tract. The location of the caudal GPi can be determined by "form fitting" the physiological map on relevant planes of a stereotactic atlas. A sensorimotor map can be developed by assessing neuronal responses to passive manipulation or active movement of the limbs and orofacial structures. The internal capsule and optic tract, respectively, can be identified by the presence of stimulation-evoked movement or the patient's report of flashes or speckles of light that occur coincident with stimulation. The optic tract may also be located by identifying the neural response to flashes of light. The anatomical/physiological map is used to guide lesion placement within the sensorimotor portion of the pallidum while sparing nearby structures, for example, the external globus pallidus, nucleus basalis, optic tract, and internal capsule. The lesion location and size predicted by using physiological recording together with thin-slice high-resolution magnetic resonance imaging reconstructions of the lesion were confirmed in one patient on histological studies.

CONCLUSIONS

These data provide important information concerning target identification for ablative or deep brain stimulation procedures in idiopathic Parkinson's disease and other movement disorders.

Surgery for dystonia

The functional organization of basal ganglia-thalamocortical circuitry and its application to surgical approaches for dystonia are discussed in this article. A model for dystonia based on neuronal recordings from patients with dystonia is presented, followed by a review of the literature concerning the role of ablative surgery for the treatment of dystonia. Lastly, alternative approaches for the surgical treatment of dystonia are discussed.

Deep brain stimulation for movement disorders

Chronic deep brain stimulation (DBS) is a promising technique for the treatment of movement disorders. Thalamic stimulation is now an established surgical procedure for parkinsonian and essential tremor. Pallidal and subthalamic stimulation are under active investigation as treatments for Parkinson's disease. Although high-frequency DBS at these sites has similar behavioral effects as lesioning, the physiologic mechanisms underlying the beneficial effect of DBS is not well understood and may be extremely complex. DBS offers a potential advantage over ablative therapy because stimulation-induced complications are reversible, and the stimulation parameters are adjustable to minimize complications and maximize therapeutic effects. With this added safety, bilateral stimulation or use of a stimulator following a prior procedure may be preferable to bilateral ablative procedures.

Visual fields in patients with posterior GPi pallidotomy

The objective of this study was to describe the incidence and types of visual field defects after posterior globus pallidus internus (GPi) pallidotomy for Parkinson's disease. The creation of the pallidotomy lesion carries a risk of damaging neighboring structures such as the optic tract. The reported frequency of visual field defects in patients after pallidotomy varies from 0 to 40%. Goldmann visual field testing was performed on 40 patients who underwent microelectrode-guided posterior GPi pallidotomy. The optic tract was identified during the procedure by listening during microelectrode recording for the evoked responses to light flashes and by assessing stimulation-induced subjective responses. After the first 18 patients, lesioning thresholds were increased from 0.5 to > or =1.0 mA so that the lesion was placed more distant from the optic tract. The location of individual lesions was determined on postsurgical MRI. Three patients (7.5%) had visual field defects likely related to the pallidotomy. These were contralateral homonymous superior quadrantanopias, associated in two patients with small paracentral scotomas. The incidence of visual field defects with the early technique was 11% (2/18) and decreased to 4.5% (1/22) after thresholds for lesioning were increased. Except for the location of the lesion relative to the optic tract (more ventral, adjacent to or extending into the optic tract), no other variable correlated with a post-pallidotomy visual field defect. Microelectrode-guided GPi pallidotomy is a relatively safe procedure as regards visual function even when the optic tract is used as a guide for lesion placement.

Pallidotomy in Parkinson's disease increases supplementary motor area and prefrontal activation during performance of volitional movements an H2(15)O PET study

Supplementary motor area and right dorsal prefrontal cortex activation in Parkinson's disease is selectively impaired during volitional limb movements. Since posteroventral pallidotomy improves motor performance in Parkinson's disease patients 'off' medication (i.e. off medication for 9-12 h), we hypothesized that it would also concomitantly increase supplementary motor area and dorsal prefrontal cortex activation. Six Parkinson's disease patients with a median total motor Unified Parkinson's Disease Rating Scale (UPDRS) of 52.5 (range 34-66) 'off' medication underwent unilateral right posteroventral pallidotomy. The patients had H2(15)O PET when 'off' medication before and 3-4 months after surgery. Each PET study comprised four to six measurements of regional cerebral blood flow either at rest or while performing regularly paced joystick movements in freely selected directions (forward, backward, left or right) using the left hand. Pre- and postoperative scans were performed in an identical manner and the associated levels of activation were compared using statistical parametric mapping. After pallidotomy, the median total motor UPDRS score 'off' medication decreased by 34.7% (P = 0.03) and mean response times of joystick movements following the pacing tones improved by 13.8% (P = 0.08). Relative increases in activation of the supplementary motor area and right dorsal prefrontal cortex were observed during joystick movements (P < 0.001). Decreased activation was seen in the region of the right pallidum (P = 0.001). We conclude that pallidotomy reduces pallidal inhibition of thalamocortical circuits and reverses, at least partially, the impairment of supplementary motor area and dorsal prefrontal cortex activation associated with Parkinson's disease.

The role of pallidotomy in Parkinson's disease and dystonia

Pallidotomy has been re-explored for the treatment of Parkinson's disease and is now being used for the treatment of medically intractable dystonia. Although initial results are favourable for both disorders, determination of the long term benefits will require well controlled clinical trials.

Tactile spatial acuity and roughness discrimination: impairments due to aging and Parkinson's disease

We used gratings of alternating ridges and grooves in a quantitative psychophysical investigation of tactile perception in patients with Parkinson's disease (PD) and age-matched normal controls. The groove width required for threshold discrimination of grating orientation was 25% higher in the control subjects compared to younger individuals studied previously (p = 0.004), indicating a small but significant decline in tactile spatial acuity with age. Relative to age-matched controls, patients with PD showed a twofold increase in the tactile spatial threshold (p = 3.07 x 10(-8), with somewhat greater impairment on the side more affected clinically (p = 0.03). Testing with the forearm prone, as compared to supine, produced a small improvement in the acuity of patients (p = 0.01) but not controls (p = 0.26). PD patients were also impaired in tactually discriminating grating roughness: their difference limens were over three times higher than those of controls (p = 5.74 x 10(-5)) for gratings differing in groove width, and over twice as high (p = 0.0003) for gratings differing in ridge width. We conclude that PD significantly impairs performance on these tactile tasks.

Burst and oscillation as disparate neuronal properties

We have developed methods to detect and discern burst and oscillatory patterns of neuronal activity. In them, a burst period is defined as an interval in which there are a significantly higher number of spikes as compared to other intervals in the spike train. Oscillation is defined as a spike train in which significant periodicity is detected in its autocorrelogram. The main feature of our burst detection method is that discharge density (i.e., the number of spikes in a short interval) is used instead of the interspike interval. This enables one to assess the likelihood of having burst periods in a spike train. We use the Lomb periodogram to detect periodicity in an autocorrelogram. This method gives one significance of periodicity detected and enables the detection of multiple frequencies in an autocorrelogram. The advantage of these methods is discussed in comparison with the other methods used to detect bursting and oscillatory activity.

Treatment of advanced Parkinson's disease by posterior GPi pallidotomy: 1-year results of a pilot study

The effects of posterior internal pallidal ablation (GPi pallidotomy) on parkinsonian signs and symptoms were studied in 15 patients with medically intractable Parkinson's disease (PD). The sensorimotor territory of the internal portion of the globus pallidus and the adjacent optic tract and internal capsule were identified with microelectrode recording and stimulation. Radiofrequency lesions were then created in the identified sensorimotor territory. Pallidotomy significantly improved all cardinal parkinsonian motor signs (tremor, rigidity, akinesia/bradykinesia, and gait dysfunction) and reduced drug-induced motor fluctuations and dyskinesias. The improvements occurred predominately contralateral to the lesion, but were also present ipsilaterally. Early postoperative (3-month), mean total United Parkinson's Disease Rating Scale scores improved by 30.1% from preoperative values. Mean combined "on/off" Schwab and England Scale scores, a measure of functional independence, increased from 48.8% to 73.0% postoperatively. The mean total United Parkinson's Disease Rating Scale and Schwab and England scores did not show a statistically significant decline over the 1-year postoperative period. Surgery resulted in little morbidity, including a lack of significant deficits on neuropsychological and psychiatric testing. Physical and social functioning and vitality measures on the Medical Outcome Scale also showed significant improvement over the postoperative period. The findings of this pilot study demonstrate that ablation of the sensorimotor portion of the internal pallidum is a highly effective treatment for advanced PD, with benefits sustained at 1 year.

Microstimulation of primate motor thalamus: somatotopic organization and differential distribution of evoked motor responses among subnuclei

1. The functional organization of motor responses to microstimulation throughout the primate "motor" thalamus including nucleus ventralis lateralis, pars oralis (VLo); nucleus ventralis posterior lateralis, pars oralis (VPLo); nucleus ventralis lateralis, pars caudalis (VLc); and portions of ventralis anterior (VA) and area X, was systematically studied in awake monkeys. A total of 2,021 sites were examined for their response to microstimulation. Of these, 1,123 were histologically verified as to their location within the motor thalamus. At or near each site, isolated neurons were examined for their responses to somatosensory examination and active movement (n = 1,272). This study was carried out as part of a larger study examining the responses of neurons in the motor thalamus to somatosensory examination, torque-induced limb perturbations, and active movement in a visuomotor step-tracking task. 2. Microstimulation at < or = 40 microA evoked movements in the contralateral limbs, trunk, or face. Evoked movements of the limb were generally maximal about a single joint. 3. There was a differential response to microstimulation between subnuclei of the motor thalamus. In order of decreasing frequency, the percentages of sites within each subnucleus from which movements were evoked were as follows: VPLo, 93% (449 of 483); VLo, 21% (57 of 272); VLc, 11% (15 of 140); VA, 1% (1 of 85); and reticular nucleus, 0% (0 of 65). In VPLc, 44% (34 of 78) of sites examined were microexcitable. However, these were almost all within 500 microns of the border of VPLo, suggesting they may have occurred as a result of current spread to adjacent VPLo. Although area X was not sampled in its entirety, it did not appear to be microexcitable. 4. Microexcitable responses had a somatotopic organization, similar to that for neuronal responses to sensorimotor examination, with leg responses found most laterally and arm and face responses found progressively more medially. 5. Zones in VPLo generally ranging from 500 to 1,500 microns were found in which microstimulation resulted in the same motor response. These microexcitable zones resemble those described for the striatum and were termed thalamic microexcitable zones (TMZ). TMZs also resemble cortical efferent zones in that both are somatotopically organized, may affect a single muscle or group of muscles, have low thresholds for microstimulation with sharp boundaries that lie adjacent to other microexcitable zones with the opposite effects, and are of approximately the same dimension. 6. This study suggest that a fundamental unit of motor organization, i.e., single muscle or joint, is preserved at the thalamic level in the form of TMZs, and that these fundamental units of organization may contribute to the modular organization of the cortex.

[The role of the basal ganglia in movement control]

It is now widely accepted that the basal ganglia (BG) are functionally organized with several segregated loops which start at a certain area in the cortex and project back to the same area in the cortex through the thalamus. The detailed functional organization of the BG motor loop has been described and used successfully to explain the mechanism of hypo- and hyper-kinetic disorders caused by BG disorders. Recent physiological and anatomical studies have provided new information concerning the function of these nuclei. The indirect pathway from the striatum to the external globus pallidus and then to the internal globus pallidus may be much more important than previous thought. The subthalamic nucleus may transmit excitatory input from the cortex as well as acting as a driving force on the globus pallidus. The role of BG output on the thalamus may not be to transfer information to the cortex via thalamocortical neurons, but rather to modulate the activity of cortico-thalamocortical loops. By varying it's discharge rate, the BG can change the membrane potentials of thalamocortical neurons which may result in focusing the activity of a specific cortico-thalamo-cortical loop and/or switching it to another.

Physiologic properties and somatotopic organization of the primate motor thalamus

1. To examine the functional organization of the primate "motor" thalamus, neuronal activity was studied systematically in awake behaving monkeys throughout the nucleus ventralis lateralis, pars oralis (VLo), nucleus ventralis posterior lateralis, pars oralis (VPLo), ventralis lateralis, pars caudalis (VLc), and portions of ventralis anterior (VA) and Area X. In addition, portions of the sensory nucleus ventralis posterior lateralis, pars caudalis (VPLc) were explored. Isolated neurons were examined for their responses to somatosensory examination and active movement (n = 919) and for their response to torque-induced joint displacements (n = 375). A total of 684 neurons was determined histologically to lie within specific subnuclei of the motor (n = 574) or sensory (n = 110) thalamus. 2. The sensorimotor response properties of neurons in the thalamic subnuclei showed clear differences in their response to somatosensory examination. In order of decreasing frequency, the percent of neurons responding to passive somatosensory examination in each subnucleus were as follows: VPLc, 96% (106/110), VPLo, 93% (252/270), VLc, 77% (43/56), VLo, 37% (59/155), Area X, 22% (12/53), and VA, 12% (5/40). Conversely, neurons that responded only to active movement were most frequent in VLo, 44% (68/155), VA, 45% (18/40), and Area X, 40% (21/53) and relatively infrequent in VLc 11% (6/56) and VPLo, 3% (7/270). In VPLc, no neurons were found that responded only to active movement (0/110). 3. A well-defined somatotopic organization was found in VLo, VPLo, and VPLc and was suggested strongly for VLc. Individual body regions were represented in a series of lamellae, organized in a partial onion skin-like arrangement with the leg represented in the outermost lamella, and the trunk, arm, and orofacial regions represented in successively deeper lamellae. In general the body representations, although present for each subnucleus thoroughly examined, i.e., VLo, VPLo, and VPLc, also were contiguous across subnuclei. Based on the available data, a clear somatotopic picture could not be discerned for Area X or VA. 4. Responses to torque application were more common in neurons in VPLo (77%; 60/78) and VLc (73%; 16/22) than in VLo (44%; 12/27). Mean latencies were shortest for neurons in VPLo (25 +/- 14 ms; mean +/- SD) and the bordering (shell) region of VPLc (22 +/- 15 ms) and were approximately twice as long in VLc (51 +/- 23 ms) and VLo (47 +/- 21 ms).(ABSTRACT TRUNCATED AT 400 WORDS)

Role of the thalamus in parkinsonian tremor: evidence from studies in patients and primate models

The electrophysiologic basis of parkinsonian tremor is discussed in terms of the central oscillator and peripheral feedback hypotheses of tremor. Recent studies in monkeys and humans suggest that parkinsonian tremor may result from the activity of a central oscillator, possibly located in the basal ganglia. Peripheral somatosensory input seems to modulate tremor and central nervous system activity related to tremor.

Diversification of health care services: the effects of ownership, environment, and strategy

The present findings suggest that the trend toward greater diversification of hospital services is likely to be most strongly influenced by state Medicaid policies and certain hospital characteristics. Increasing Medicaid eligibility and payment levels is likely to have a positive effect on services diversification. Growth in the number of inpatient services provided and a more severe case mix are also likely to be involved with greater service diversification. Affiliation with a not-for-profit hospital system is likely to be associated with more diversified hospital services but not affiliation with an investor-owned system. There is also some indication that the overall portfolio of services which a hospital offers in regard to market share and market growth characteristics influences diversification. Specifically, a low market share portfolio is likely to be associated with less diversification. Competition is likely to be associated with more diversification; particularly for hospitals belonging to systems. The effect of competition on hospital strategy and services diversification is a particularly important area for further investigation. Increasing Medicaid payment and eligibility levels are also likely to have a positive effect on the provision of services which are usually unprofitable. Raising such levels is likely to be particularly beneficial to inner-city hospitals who are already providing a greater number of such services. However, the present data suggest that investor-owned hospitals are least likely to provide such services. Increasing Medicaid eligibility levels is also likely to be associated with fewer services for which charity care has to be provided. State regulation in the form of rate review and certificate of need is likely to be associated with more services for which hospitals provide some charity care. But such policies alone do not deal with the larger issue of how to finance care for the medically indigent. Present data suggest the charity care issue may be particularly salient in markets characterized by a relatively high degree of competition. Finally, investor-owned hospitals provide as many services involving charity care as not-for-profit system hospitals, although investor-owned system hospitals provide fewer such services than not-for-profit freestanding hospitals. Throughout, the findings indicate the importance of distinguishing between ownership and system affiliation. Previous research has failed to make a distinction between ownership form and system affiliation, thus attributing to ownership form differences which, as present findings suggest, appear to be more associated with system affiliation.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of cerebellar stimulation on the stretch reflex in the spastic monkey

The effects of stimulating the cerebellar surface on abnormal segmental reflexes were examined in monkeys rendered spastic by either bilateral or unilateral decortication of areas 1, 2, 3, 4 and 6. Rectified, integrated electromyographic (EMG) activity from the biceps and triceps as well as the torque were recorded and averaged during successive flexion-extension movements of the arm produced by a displacement controlled torque motor. Two movement paradigms were employed. The first consisted of a ramp and hold paradigm with an initial rapid flexion of the forearm, a subsequent two second period during which the arm position was held constant, and a rapid extension returning the limb to the initial position. In the second paradigm, the forearm was modulated sinusoidally at several different frequencies. Cerebellar stimulating electrodes were placed over the paravermal region bilaterally. Different frequencies (10 to 300 HZ) and different charge densities (1.5 to 10 microC/cm2) were used in each animal. In each experimental trial short periods of cerebellar stimulation (10 to 30 minutes) were interspersed between control periods. As observed in some types of clinical spasticity, flexion or extension of the extremity was capable of evoking coactivation of the biceps and triceps. Cerebellar surface stimulation reduced the amplitude of the phasic and tonic stretch reflexes recorded from the triceps during flexion and decreased the abnormal triceps response during passive shortening. The biceps response to stretch was increased by cerebellar stimulation and its abnormal response to flexion was decreased. These combined effects modified the organization of the segmental reflexes, producing a more normal reciprocal relationships of the EMG activity in the biceps and triceps. Evaluation of many different combinations of stimulus parameters revealed that not only the magnitude of the passive reflex but also the nature of the effect was dependent on stimulus parameters. Although these studies demonstrate an improvement in the abnormal reflexes present in spastic primates, they emphasize the complexities of the response evoked by cerebellar stimulation and the importance of stimulus parameters in the modifications produced by this technique.