Gian Emilio Chatrian

The significance of periodic lateralized epileptiform discharges in EEG: An electrographic, clinical and pathological study☆☆☆

Abstract Periodic lateralized epileptiform discharges (PLEDs) were recorded in 33 subjects. In their most typical form the PLEDs consisted of sharp wave discharges repeating periodically or quasi-periodically at rates generally close to 1/sec and separated by intervals of apparent quiescence. Twenty-nine of 33 patients experienced epileptic seizures consisting of epilepsia partialis continua in seven cases, reiterative, sporadic or isolated focal motor seizures in eighteen cases and continuous psychical seizures in four cases. Four subjects did not present detectable clinical signs of seizure activity. All patients with PLEDs exhibited other symptoms and signs of impaired neurological and mental function, motor and sensory deficits, visual field defects and alterations of symbolic functions. The etiology of the lesion(s) or disorders was: cerebral infarct(s) in thirteen cases, recent infarct or chronic focal seizure disorder in seven cases, chronic focal seizure disorder in three cases, space-occupying lesion (metastases and glioblastomas) in eight cases, pneumococcal meningitis in one case and post-vaccinal encephalomyelitis in one case. Twenty-four subjects suffered from uremia, alterations of fluid, electrolyte and acid-base balance, impairment of liver function (18 cases) and/or had histories of previous epileptic seizures (7 cases) and chronic alcoholism (12 cases). The role played in these focal seizure disorders by local anoxia, systemic metabolic derangements, alcohol withdrawal and pre-existing convulsive disorders is discussed. Most of the cases ran fairly benign courses with recovery in a few days to several weeks. In six of twelve patients who expired, autopsy was obtained. Correlation of the electrographic, clinical and pathological findings suggested that the central cortex implicated in the seizure discharge was generally the farthest from the anatomical lesion. Maximal increase of cerebral excitability peripheral to the bulk of the edema and of the metabolic derangement surrounding the lesion may account for this discrepancy. Between the site of lesion and general neurologic and electrographic abnormalities better correlation was found.

Cerebral responses to electrical tooth pulp stimulation in man An objective correlate of acute experimental pain

The pulp of individual teeth of 17 normal adult volunteers was electrically stimulated via pairs of electrodes implanted into dentine. Computer-summated responses recorded from the surface of the head were composed of two concurrent sequences of events, one of which was seen maximally over midline areas and the other over the lower portions of the postcentral regions. Appropriate tests demonstrated that these wave forms represented cerebral tooth pulp-evoked potentials. Because tooth pulp-evoked potentials represent objective, quantifiable, nonverbal concomitants of central events associated with the perception of noxious stimuli, they may prove helpful in investigating acute experimental pain in man.

Retinitis Pigmentosa: A Symposium on Terminology and Methods of Examination

This report represents a summary of opinions expressed at a meeting of specialists interested in retinitis pigmentosa (RP) and allied diseases, at which an attempt was made to define some minimum guidelines for ocular evaluation of these disorders. The term RP would be reserved for a group of hereditary disorders that diffusely involve photoreceptor and pigment epithelial function, and should not be used when a secondary cause is suspected. RP may be classified by genetic type (single cases without known affected relatives should be termed isolated or simplex), by the topography of retinal involvement, and by the severity of disease (to identify subtypes with mild or localized disease). Patients should have at least one comprehensive examination that conforms to basic standards, preferable early in the course of the disease. The visual field examination should use both a small and a large test light. Electroretinographic testing should (1) use a full-field stimulus, and (2) routinely document three independent responses (cone, rod, and mixed cone-rod). Patients should be identifiable for future study or therapeutic trials. They should be counseled about the disease and followed regularly. No specific therapy exists at present for most of these diseases, but optical and night vision aids are available. Sunglasses for outdoor use are recommended until more is known about whether long-term exposure to bright sunlight alters the course of these diseases.

EEG PATTERN RESEMBLING WAKEFULNESS IN UNRESPONSIVE DECEREBRATE STATE FOLLOWING TRAUMATIC BRAIN-STEM INFARCT.

Abstract A case is described of an unresponsive decerebrate state following infarct of the pons and of the lowermost portion of the midbrain due to traumatic occlusion of the basilar artery. This patient exhibited an EEG pattern which was similar to that of a waking subject but which remained unmodified by somatic and auditory stimuli. The physiological implications of this finding are discussed.

Long-term EEG-video-audio monitoring: computer detection of focal EEG seizure patterns ☆

Twelve individuals with medically refractory partial seizures had undergone EEG-video-audio (EVA) monitoring over 1-15 (mean 10.5) days. We selectively reexamined available 15-channel EEGs (video-cassettes) totaling 461 h and containing 253 EEG focal seizures. Computer analysis (CA) of these bipolar records was performed using a mimetic method of seizure detection at 6 successive computer settings. We determined the computer parameters at which this method correctly detected a reasonably large percentage of seizures (81.42%) while generating an acceptable rate of false positive results (5.38/h). These parameters were adopted as the default setting for identifying focal EEG seizure patterns in all subsequent long-term bipolar scalp and sphenoidal recordings. Factors hindering or facilitating automatic seizure identification are discussed. It is concluded that on-line computer detection of focal EEG seizure patterns by this method offers a satisfactory alternative to and represents a distinct improvement over the extremely time consuming and fatiguing off-line fast visual review (FVR). Combining CA with seizure signaling (SS) by the patients and other observers increased the correct detections to 85.38% CA is best used in conjunction with SS.

Electrical stimulation of tooth pulp in humans. I. Relationships among physical stimulus intensities, psychological magnitude estimates and cerebral evoked potentials

Abstract Brief electrical pulses were applied to the pulp of individual pre‐molar teeth of 14 healthy, adult volunteers via wire electrodes implanted and sealed in dentine. The sensation threshold was estimated in each individual by the Two‐Alternative Forced‐Choice Staircase (2AFCS) method. Seven, 5 or 4 stimulus intensities were employed which were equally spaced in a logarithmic scale between 10 &mgr;A above threshold and 500 &mgr;A. Magnitude estimates of the subjective intensity of the sensation produced by individual dental excitations were obtained. Cerebral tooth pulp‐evoked potentials were simultaneously recorded in 11 subjects. The growth of psychological sensory magnitude with increasing strength of electrical stimulus conformed to the general psychophysical power law. Individual power function exponents varied from 0.204 to 0.907 with a mean of 0.475 and a standard deviation of 0.190. The amplitude of TPEPs, measured between components N135 and P293, also was a power function of stimulus intensity. The exponents of individual TPEP amplitude‐intensity functions ranged from 0.055 to 0.362 with a mean of 0.144 and a standard deviation of 0.100. These last exponents were substantially smaller than those describing the growth of psychological magnitude estimates. Neither magnitude estimation nor TPEP amplitude‐intensity functions displayed abrupt changes in slope which might accompany transition from one operating sensory mechanism to another and/or changes in qualities of subjective sensations from ‘innocuous’ to ‘uncomfortable’ to ‘painful.’ The result of our psychophysical and electrophysiologic experiments indicate That: (1) albeit highly specialized both morphologically and functionally, human tooth pulp has certain fundamental properties in common with other sensory systems and (2) late midline TPEP components may provide measures of central events that, within a range of stimulus itensities, are associated with the perception of pain, but should not be looked upon as specific indicators of pain processes.

electrical stimulation of tooth pulp in humans. II. Qualities of sensations

Abstract Individual premolar teeth of 22 normal volunteers were stimulated via intradentinal electrodes using brief electrical pulses. Questionnaires were used to determine the qualities of sensations produced by this stimulation. Operationally defined “innocuous’ sensations predominated between 1 and 10 dB SL, and were absent above 30 dB SL. Similarly defined ”painful’ sensations were observed throughout the range of suprathreshold intensities but were most common above 20 dB SL.‘Uncomfortable’ sensations were especially frequent between 1 and 20 dB SL. These findings demonstrate that non‐painful sensations can arise from electrical tooth pulp excitation in circumstances in which spread of the stimulating current to periodontal and gingival structures is most unlikely. Two interpretations of these results are considered: (1) that tooth pulp afferents may have some unspecified sensory function besides mediation of painful sensations and (2) that they may be specialized in the mediation of nociceptive impulses but may give rise to innocuous sensations under special circumstances.

Positive occipital sharp transients of sleep: Relationships to nocturnal sleep cycle in man

Abstract Overnight polygraphic recordings were performed on 6 subjects who had normal diurnal waking and sleep EEGs and no significant findings on neurological examination. These individuals displayed prominent physiologic “positive occipital sharp transients of sleep” (POSTS) which were visually counted and related to the nocturnal sleep cycle. POSTS were numerous during all stages of NREM sleep and occurred more frequently during stages 2 and 3 than 1 and 4. On the contrary, they were absent or very rare during REM sleep. Striking similarities existed between these potentials and the lambda waves (LWs) occurring in waking subjects intent at visually exploring an illuminated patterned field. The hypothesis is proposed that POSTS of human subjects might indicate that some form of “playback” of information takes place during NREM sleep in cortical areas related to vision. The purpose of this postulated playback might be to re-examine vast amounts of visual material collected during the day, perhaps with the intent of sorting, analyzing further and compressing novel, relevant data for long-term memory storage while simultaneously rejecting redundant and/or irrelevant information.

Electrocorticography in patients with medically intractable temporal lobe seizures. II. Quantification of epileptiform discharges following successive stages of resective surgery

We quantified retrospectively the interictal epileptiform discharges (EDs) detected visually in the electrocorticograms (ECoGs) of 42 patients undergoing successive stages of anterior temporal lobectomy for medically intractable temporal lobe seizures (TLS). Following first resection sparing the hippocampus (H) and the parahippocampal gyrus (PHG), EDs were recorded on both structures in all patients and by far exceeded in amount those on residual lateral infratemporal and lateral temporal cortices. Frequently, EDs occurred apparently simultaneously but with opposite polarities on the H and the PHG, but more complex relationships were also evident in most individuals. These features likely reflected abnormal post-synaptic activity generated at different locations and cortical depths within the H, PHG, or both. Quantification of epileptiform activity and the effects of selective anterior hippocampectomy or parahippocampectomy suggested that both the H and PHG had remarkable epileptogenic potential. Levels of epileptiform activity were not significantly different in the H and PHG and in the H of subjects with and without H sclerosis. After final resection, including the amygdaloid nucleus (AN), anterior H and PHG, interictal EDs were present, although markedly diminished, in 35 patients. Postresection foci were significantly less numerous and extensive, and attained smaller maximal voltages, than did foci before and after first resection.

FOCAL PERIODIC SLOW TRANSIENTS IN EPILEPSIA PARTIALIS CONTINUA: CLINICAL AND PATHOLOGICAL CORRELATIONS IN TWO CASES.

Abstract Two cases of epilepsia partialis continua with pathological documentation are described. Periodic focal negative or negative-positive potential changes occurred in the EEG of these patients. These slow transients are interpreted as local shifts of the steady potential of the cerebral cortex recorded transcranially. Their relationships to the focal epileptic discharge are discussed.