Prognostic Value of Preoperative Flash and Pattern Visual Evoked Potentials for Diabetic Retinopathy Vitrectomy

In view of the continuing controversy about the prognostic value of preoperative visual evoked potentials in diabetic vitrectomy, we retrospectively studied 31 eyes undergoing vitrectomy for diabetic retinopathy after recording pattern and/or flash visual evoked potential recording. Preoperative pattern visual evoked potentials were of no prognostic value in these eyes but a decrease in the amplitude of preoperative flash visual evoked potentials was significantly correlated with unchanged or worsened postoperative visual acuity when compared with preoperative visual acuity (P = 0.0156, Fisher's exact test). Therefore, while acknowledging that diabetic vitrectomy functional prognosis is actually multifactorial, we still recommend recording preoperative flash visual evoked potentials for diabetic patients in whom significant opacities of the intraocular media preclude correct examination of the ocular fundus, because a decrease in peak III amplitude may indicate a guarded vitrectomy functional prognosis.

How clinical neurophysiology may contribute to the understanding of a psychiatric disease such as schizophrenia

INTRODUCTION

The increasing knowledge about anatomical structures and cellular processes underlying psychiatric disorders may help bridge the gap between clinical manifestations and basic physiological processes. Accordingly, important insights have been brought these last years into a main psychiatric affection, i.e. schizophrenia.

MATERIAL AND METHODS

Here we reviewed and described, by comparison to healthy people, different physiological parameters - oculomotor measures, startle response, and cognitive event related potentials, which are altered in schizophrenia, in order to link these physiological parameters to dysfunctional cognitive processes and specific clinical symptoms.

RESULTS

Schizophrenic patients displayed: (1) abnormalities in smooth pursuit eye movements and saccadic inhibition during antisaccade tasks that may stem from the same prefrontal "inhibitory" cortical dysfunction; (2) deficits in prepulse inhibition and facilitation suggesting disturbed attentional modulations, which seem also correlated to abnormal patterns of prefrontal activation; and (3) decreased amplitude for cognitive ERP situated all along the continuum of the information processing, suggesting that schizophrenia shows neurophysiological deficits since the level of the sensory cortex and not only disturbances involving associative cortices and limbic structures.

DISCUSSION

The heterogeneity of schizophrenic disorders regarding symptomatology, course, and outcome is underlain by various pathophysiological processes that physiological parameters may help define. These alterations may be related to precise cognitive processes that are easily neurophysiologically monitored in order to create more homogeneous subgroups of schizophrenic patients.

Recommendations for the clinical use of somatosensory-evoked potentials

The International Federation of Clinical Neurophysiology (IFCN) is in the process of updating its Recommendations for clinical practice published in 1999. These new recommendations dedicated to somatosensory-evoked potentials (SEPs) update the methodological aspects and general clinical applications of standard SEPs, and introduce new sections dedicated to the anatomical-functional organization of the somatosensory system and to special clinical applications, such as intraoperative monitoring, recordings in the intensive care unit, pain-related evoked potentials, and trigeminal and pudendal SEPs. Standard SEPs have gained an established role in the health system, and the special clinical applications we describe here are drawing increasing interest. However, to prove clinically useful each of them requires a dedicated knowledge, both technical and pathophysiological. In this article we give technical advice, report normative values, and discuss clinical applications.

Stump pressure and somatosensory evoked potentials for predicting the use of shunt during carotid surgery

The aim of this study is to compare measurement of stump pressure (SP) and somatosensory evoked potentials (SSEP) made during carotid surgery as criteria upon which to base the decision whether or not to use a shunt. We included 288 patients who underwent for carotid surgery under general anaesthesia. We performed 247 endarterectomies with patch closure (85.7%), 25 carotid transsection with reimplantation (8.7%), and 16 carotid bypasses (5.6%). SSEP monitoring showed no modification in 225/288 patients (78.1%), moderate modification in 32/288 patients (11.1%), and severe modification in 31/288 patients (10.8%). Shunt was used if there was moderate or severe SSEP modification in response to carotid clamping, which represents 63 patients in our series. A shunt was used in 47/288 patients (16.3%). In 16 patients, despite SSEP modifications, the shunt was not used because these SSEP modifications occurred only in the last minutes of the procedure just before off clamping the carotid. The mean SP for all patients was 51 mm Hg. In the shunted patients, the mean SP was 33 mm Hg. Variation of SP was correlated with the SSEP modifications. There was just one perioperative stroke in this series (1/288 = 0.3%). We concluded that the threshold of SP below which shunting is indicated in our study was 44 mm Hg with 81% sensibility and 68% specificity.

The EEG assessment of low-grade hepatic encephalopathy: Comparison of an artificial neural network-expert system (ANNES) based evaluation with visual EEG readings and EEG spectral analysis

OBJECTIVE

The EEG provides an objective staging of hepatic encephalopathy (HE), but its interpretation may be biased by inter-observer variability. This study aims at comparing an entirely automatic EEG classification of HE based on an artificial neural network-expert system procedure (ANNES) with visual and spectral analysis based EEG classifications.

METHODS

Two hundred and thirty-eight consecutive cirrhotic patients underwent closed-eye EEG. They were followed up for up to one-year to detect bouts of overt HE and death. The EEG was classified by ANNES, qualitative visual reading, main basic rhythm frequency and spectral analysis. The classifications were assessed on the basis of: (i) match with liver function, (ii) prognostic value and (iii) repeatability.

RESULTS

All classifications were found to be related to the severity of liver failure, with cognitive findings and a history of previous bouts of HE. All of them had prognostic value on the occurrence of overt HE and on survival. The ANNES based classification was more repeatable than the qualitative visual one, and had the advantage of detecting low power EEG, but its efficiency in analyzing low-grade alterations was questionable.

CONCLUSIONS

An entirely automatic - ANNES based - EEG classification of HE can improve the repeatability of EEG assessment, but further improvement of the device is required to classify mild alterations.

SIGNIFICANCE

The ANNES based EEG grading of HE needs further improvements to be recommended in clinical practice, but it is already sufficient for detecting normal and clearly altered EEG tracings.

Assessment of olfactory and trigeminal function using chemosensory event-related potentials

GOALS

To give an overview on the theoretical and practical applications of chemosensory event-related potentials.

METHODS

Chemosensory event-related potentials (ERPs) may be elicited by brief and precisely defined odorous stimuli. Based on the principles of air-dilution olfactometry, a stimulator was developed in the late 1970s, which allows stimulation of the olfactory neuroepithelium and the nasal mucosa with no concomitant mechanical stimulation. Chemosensory ERPs were obtained after stimulation of the olfactory nerve (olfactory ERPs) or the trigeminal nerve (somatosensory or trigeminal ERPs). The characteristics of the stimulator for chemosensory research as well as the variables influencing the responses are discussed in this paper.

RESULTS

Implementation and normative data from our department are reported with different clinical examples from otorhinolaryngologic clinic. The bulk of the evoked response consists of a large negative component (often referred to as N1), which occurs between 320 and 450 ms after stimulus onset. This component is followed by a large positive component, often referred to as P2, occurring between 530 and 800 ms after stimulus onset. Absence of olfactory ERPs and presence (even with subtle changes) of somatosensory ERPs is a strong indicator of the presence of an olfactory dysfunction.

CONCLUSIONS

This review examines and discusses the methods of chemosensory stimulation as well as the electrophysiological correlates elicited by such stimuli. The clinical applications of chemosensory ERPs in neurology and otorhinolaryngology are outlined.

Recording click-evoked myogenic potentials (CEMPs) with a setup for brainstem auditory evoked potentials (BAEPs)

AIM OF THE STUDY

Click-evoked myogenic potentials (CEMPs) originate in the sternocleidomastoid (SCM) muscle through a reflex loop involving the sacculus and the vestibular nerve. In this study we suggest that they can be picked up from the mastoid reference used for auditory evoked potential (AEP) recording by using standard filters for brainstem AEPs (BAEPs). They consist of a P13-N20 complex.

METHODS

Fifty normal subjects were investigated. Recordings were performed with the same setting as that used for conventional BAEPs but without artifact rejection and using a wide time window (100 ms). Unilateral auditory stimulations were used. All acquisitions were performed in both sitting and supine positions. In nine subjects CEMPs and BAEPs were simultaneously recorded at both earlobe and both SCM muscles.

RESULTS

In all subjects, a CEMP P13-N20 component could be evidenced in sitting, but not in supine position at both the ipsilateral earlobe and the ipsilateral SCM muscle. Its latency was 0.7 ms lower at the earlobe. It obeyed the same relationship to stimulus intensity at both earlobe and SCM muscle.

CONCLUSION

These results demonstrate the possibility to get simultaneous information on the brainstem auditory pathways and on a reflex probably mediated through the sacculus and the vestibular nerve. Further studies on patients with selective vestibular nerve impairment should be conducted to confirm the clinical utility of this approach.

The electrophysiological correlates sustaining the retrieval of face-name associations: An ERP study

An ERP study on 9 healthy participants was carried out to temporally constrain the neural network proposed by Campanella et al. (2001) in a PET study investigating the cerebral areas involved in the retrieval of face-name associations. Three learning sessions served to familiarize the participants with 24 face-name associations grouped in 12 male/female couples. During EEG recording, participants were confronted with four experimental conditions, requiring the retrieval of previously learned couples on the basis of the presentation of name-name (NN), face-face (FF), name-face (NF), or face-name (FN) pairs of stimuli. The main analysis of this experiment consisted in the subtraction of the nonmixed conditions (NN and FF) from the mixed conditions (NF and FN). It revealed two main ERP components: a negative wave peaking at left parieto-occipital sites around 285 ms and its positive counterpart recorded at left centro-frontal electrodes around 300 ms. Moreover, a dipole modeling using three dipoles whose localization corresponded to the three cerebral areas observed in the PET study (left inferior frontal gyrus, left medial frontal gyrus, left inferior parietal lobe) explained more than 90% of the variance of the results. The complementarity between anatomical and neurophysiological techniques allowed us to discuss the temporal course of these cerebral activities and to propose an interactive and original anatomo-temporal model of the retrieval of face-name associations.

Discrimination of emotional facial expressions in a visual oddball task: an ERP study

Several ERP studies have shown an orienting complex, the N2/P3a, associated to the detection of stimulus novelty. Its role consists in preparing the organism to process and react to biologically prepotent stimuli. Whether this N2/P3a: (1) could be obtained with complex visual stimuli, such as with emotional facial expressions; and (2) could take part in a complex discrimination process has yet to be determined. To investigate this issue, event-related potentials were recorded in response to repetitions of a particular facial expression (e.g. sadness) and in response to two different deviant (rare) stimuli, one depicting the same emotion as the frequent stimulus, while the other depicted a different facial expression (e.g. fear). As expected, deviant stimuli evoked an N2/P3a complex of larger amplitude than frequent stimuli. But more interestingly, when the deviant stimulus depicted the same emotion as the frequent stimulus the N2/P3a was delayed compared to the response elicited by the different-emotion deviant. The N2/P3a was thus implicated in the detection of physical facial changes, with a higher sensitivity to changes related to a new different emotional content, perhaps leading to faster adaptive reactions.

Categorical perception of happiness and fear facial expressions: an ERP study

Behavioral studies have shown that two different morphed faces perceived as reflecting the same emotional expression are harder to discriminate than two faces considered as two different ones. This advantage of between-categorical differences compared with within-categorical ones is classically referred as the categorical perception effect. The temporal course of this effect on fear and happiness facial expressions has been explored through event-related potentials (ERPs). Three kinds of pairs were presented in a delayed same-different matching task: (1) two different morphed faces perceived as the same emotional expression (within-categorical differences), (2) two other ones reflecting two different emotions (between-categorical differences), and (3) two identical morphed faces (same faces for methodological purpose). Following the second face onset in the pair, the amplitude of the bilateral occipito-temporal negativities (N170) and of the vertex positive potential (P150 or VPP) was reduced for within and same pairs relative to between pairs. This suggests a repetition priming effect. We also observed a modulation of the P3b wave, as the amplitude of the responses for the between pairs was higher than for the within and same pairs. These results indicate that the categorical perception of human facial emotional expressions has a perceptual origin in the bilateral occipito-temporal regions, while typical prior studies found emotion-modulated ERP components considerably later.

Sensitivity, specificity, and surgical impact of somatosensory evoked potentials in descending aorta surgery

BACKGROUND

We evaluate the efficiency of multilevel somatosensory evoked potential (SEP) monitoring for intraoperative re-establishment of blood flow to the spinal cord in 63 patients undergoing descending aorta repair.

METHODS

The presence of critical vessels in a cross-clamped aortic segment was ascertained by a 15 minute SEP observation period while the segment between the clamps was vented to drain out the collateral flow.

RESULTS

SEPs influenced the surgical strategy in 17 cases (27%): use of the Biomedicus in 1 traumatic rupture; critical vessel reimplantation or distal clamp replacement in 13 cases of segmental spinal ischemia; and hastening the procedure or proximal clamp replacement in 3 cases of left carotid ischemia. There were no cases of unexplained multilevel SEP abnormalities. Immediate paraplegia was observed in 2 cases (1 pre-existing; 1 forecast by a 199-minute period of SEP absence due to segmental ischemia); 2 patients presented delayed paraplegias despite unchanged intraoperative SEPs, and 1 case presented a transient paraplegia due to lower motoneuronal involvement.

CONCLUSIONS

SEPs efficiently identified critical vessels to be reimplanted in order to avoid immediate paraplegia. However, systematic additional vessel reimplantation, if technically feasible, and prolongation of SEP monitoring during the postoperative period with careful blood pressure control are needed to prevent delayed paraplegia.

Retrospective study of somatosensory evoked potential monitoring in deep hypothermic circulatory arrest

BACKGROUND

We evaluated the efficiency of median-nerve somatosensory evoked potentials (SEPs) monitoring in determining the optimal level of hypothermia in 62 consecutive patients operated on under deep hypothermic circulatory arrest (CA).

METHODS

CA was started at 1 degree C below the temperature at which both brainstem and cortical SEP components disappear. No additional method of cerebral protection was used.

RESULTS

New neurological complications were observed in 15 patients: long-lasting in 11 and transient in 4. A retrospective analysis of SEP monitoring identified the origin of the complications in 12 cases: early CA with incomplete cooling due to emergency (3 cases); inefficient retrograde perfusion through the femoral artery during cooling due to the dissection flap effect (4 cases); embolism during rewarming (2 cases); delayed embolism (2 cases); hemorrhagic shock (1 case). In 2 cases, neurological sequelae involved the lower limbs (extracerebral origin). One case without intraoperative SEP changes was neurologically abnormal preoperatively and did not change postoperatively. There were no cases with sequelae due to excessive CA duration.

CONCLUSIONS

The use of SEP monitoring to determine the optimal level of hypothermia efficiently prevents neurological sequelae of CA. It helps in monitoring the degree of cerebral protection during cooling (flap effect), and rewarming.

Task modulation of brain activity related to familiar and unfamiliar face processing: an ERP study

In order to investigate stimulus-related and task-related electrophysiological activity relevant for face processing, event-related potentials (ERPs) from 58 electrodes at standard EEG sites were recorded while subjects performed a simple visual discrimination (control) task, in addition to various face processing tasks: recognition of previously learned faces and gender decision on familiar and unfamiliar faces. Three electrophysiological components or dipolar complex were recorded in all subjects: an occipital early component (P1, around 110 ms); a vertex positive potential (VPP; around 158 ms) which appeared to be specific to faces; and a negative central component, N2 (around 230 ms). Parametric analysis and source localization were applied to these components by means of a single-subject analysis methodology. No effect of familiarity was observed on any of these early component. While the VPP appears to be independent of the kind of processing performed, face task modulations of the early P1 and the N2 were observed, with a higher amplitude for the recognition than for the gender discrimination task. An attentional modulation of early visual areas is proposed for the first effect (P1 modulation), while the N2 seems to be related to general visual memory processing. This study strongly suggests that the VPP reflects an early visual stage of face processing in the fusiform gyrus that is strictly stimulus-related and independent of familiarity. It also shows that source localization algorithms may give reliable solutions on single subject averages for early visual components despite high inter-subject variability of the surface characteristics of ERPs.

Sciatic nerve regeneration in the rat after frozen muscle grafting. A comparative study using somatosensory evoked potentials

In an experimental study, somatosensory evoked potentials were used to evaluate sciatic nerve regeneration in the rat after 12 mm-long conventional nerve grafting, vascularized nerve grafting and frozen muscle grafting. This experimental method was found to be technically easy and highly reproducible. No statistical difference was found between the three groups concerning amplitude of the negative electrical wave recorded at the cortex level after distal stimulation. Conduction velocities were found to be significantly higher in both the vascularized nerve group and the frozen muscle group, compared with the conventional nerve grafting group. The frozen muscle grafting technique is valuable as it gives good experimental results, is easy to carry out and causes minimal damage to the donor site.

Bilateral tonic pupils and polyneuropathy in Sjögren's syndrome: a common pathophysiological mechanism?

One case associating tonic pupils and Sjögren's syndrome is reported. Neurophysiological examination also demonstrated a purely sensory neuropathy. This rare association raises the issue of a common process destroying the ciliary and spinal root ganglia in these patients.

Subacute sensory neuronopathy associated with Sjögren's sicca syndrome

Sensory subacute neuropathies associated with sicca syndrome without any systemic involvement have been reported rarely. A sixth case is described with what appears to be the first report of muscle and nerve biopsy findings. The histological studies revealed axonal degeneration without vasculitis in the sural nerve, and a slight denervation process and a discrete myositis in the gastrocnemius muscle, reflecting a subtle systemic disorder. The clinical course of a long-standing subacute sensory neuropathy, the biopsy-documented axonal degeneration, and the neurophysiological findings suggest involvement of the dorsal root ganglia.

Unexpected myogenic contaminants observed in the somatosensory evoked potentials recorded in one brain-dead patient

Visual, brain-stem auditory and somatosensory evoked potentials (EPs) have been recorded in a 53-year-old woman who fulfilled all criteria of brain death. We observed the persistence of 48 msec latency somatosensory activities. Their muscular, and not neural, origin was, however, suggested by their disappearance after curarization. The practical consequences of this observation are two-fold. On the one hand, more precautions must be taken before reaching the conclusion that central neural activities can be obtained in coma dépassé patients. On the other, it suggests a possible test to enhance the sensitivity of EPs in diagnosing brain death.

Pudendal cortical somatosensory evoked potentials

To determine normal reference latencies pudendal cortical somatosensory evoked potentials were evaluated in 20 healthy volunteers. The dorsal nerve of the penis or clitoris was stimulated electrically and the cortical response was recorded from the CZ-2 point (2 cm. behind the central vertex). Reproducible responses were obtained and reference values were established.

Applications of surface-recorded auditory evoked potentials for the early diagnosis of hearing loss in neonates and premature infants

The recording of Auditory Evoked Potentials (AEPs) in adults provides a non-invasive means of assessing the auditory system at its peripheral and central levels. In neonates and premature babies, technical, methodological and physiological constraints prevent the clinician from simply extrapolating from the adult data. Those constraints are discussed. In the light of this discussion, some limits on the validity of AEP recording in very young patients are proposed.

Hemispheric differences in the voluntary inhibition of movement

Twenty normal, twenty left-, and fifteen right-brain injured subjects, all right-handed, were assigned a sequence of voluntary inhibition of 23 movements. The inhibition lapse was recorded. Statistical analyses indicated a high performance in the normal and a deficient performance in left-brain injured subjects, no influence of the neurological symptoms on groups' achievement, a handicap in the subjects affected by a frontal lesion in the right brain, a hierarchical clustering of items varying according to the groups, and an organ-group interaction.

The influence of ototoxic drugs on brainstem auditory evoked potentials in man

To examine the short- and long-term consequences of ototoxic drug administration, the brainstem auditory evoked potentials (BAEP) have been recorded in patients undergoing treatment with aminoglycosides antibiotics. It appears that the rapidity of the i.v. injection influences the short-term consequences of the drug administration. The long-term consequences may be reversible. Their reversibility could depend on the status of the ear before the first injection of ototoxic drug. In conclusion, BAEP may be useful as a means of atraumatic monitoring of the auditory function of patients treated with aminoglycosides antibiotics, the non-invasive character of this technique allowing it to be repeatedly used in both adult and young patients.