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Biomedical subjects

C D Binnie

Publications and source records attributed to C D Binnie.

At least 127 records · Page 7Linked to original sources
PubMed1985

Mechanisms of epileptogenesis in photosensitive epilepsy implied by the effects of moving patterns.

The triggering of epileptiform EEG discharges by pattern is thought to depend on the intensity of excitation within the visual cortex. The present study investigates the role of the synchronisation of neuronal activity by the stimulus. In 10 pattern-sensitive subjects the effects of the following patterns have been compared: (1) static gratings, (2) gratings oscillating in a direction orthogonal to the lines (which should synchronise activity in direction-sensitive cortical units), and (3) gratings drifting at the same angular velocity (which should produce little or no synchronisation, because the contours enter and leave the overlapping receptive fields of individual neurones asynchronously). The oscillating gratings were most, and the drifting least, epileptogenic. In 2 further subjects oscillating and phase-reversing patterns were more epileptogenic than drifting gratings. Although open to alternative explanations, the findings conform with predictions from the hypothesis that synchronisation of individual cortical neurones by the stimulus contributes to epileptogenesis in photosensitive subjects.

Adolescent↗
PubMed1985

Geniculate spikes during epileptic seizures induced in dogs by pentylenetetrazol and bicuculline.

Previous studies have indicated that in cats generalized seizures induced by pentylenetetrazol (PTZ) or bicuculline (BIC) may be preceded by high frequency multi-unit activity in brain-stem structures. This activity is not readily demonstrable using conventional EEG recording bandwidths and precedes the onset of spikes and spikes-wave activity in thalamo-cortical systems. Recording with chronic subdural and depth electrodes during PTZ and BIC-induced seizures in 18 dogs essentially replicated these results. However, a new and consistent finding was that the high frequency discharges accompanying seizure onset were most often seen, and most often appeared first, in the lateral geniculate body, neocortex and hippocampus being involved later. The findings are considered to suggest a significant role for subcortical structures in this particular model of generalized cortico-reticular epilepsy.

Animals↗
PubMed1985

Electrophysiological and hormonal responses to three types of electroconvulsive therapy.

Patients were treated with three different types of electroconvulsive therapy in random order in the first three sessions of their courses. Anaesthetic and muscle relaxants were administered in standard doses, and treatment applied a set time after bolus injection. Electroencephalographic recordings were undertaken before, during, and after treatment, and hormonal measures before and after. The responses to treatment differed between the three types of current in both EEG and prolactin measures. It is suggested that the quality of the convulsive response varies with different currents.

Adult↗
PubMed1985

Assessment of effects of antiepileptic drugs.

Pharmacological studies form an important adjunct to epilepsy monitoring and conversely long-term EEG and video recording are of value for assessing antiepileptic drug (AED) effects. Clinical estimates of the incidence of brief frequent seizures as absences is often difficult but greater reliability can be achieved by long-term monitoring of the seizures themselves or of the associated EEG discharges. There are, however, very marked spontaneous short-term fluctuations in discharge rates and the amounts of ictal epileptiform activity in short conventional EEGs rarely provide any useful index of AED action. Acute investigations are of value for assessing new AEDs or experimental methods of administration and for pharmacokinetic studies. For this purpose either spontaneous EEG discharges or photosensitivity may provide quantitative measures of antiepileptic effect. Long-term AED monitoring by means of an indwelling catheter indicates the time course of blood drug levels to be more complex and variable than might be expected from simple pharmacokinetic models. Short-term fluctuations in AED concentrations have little effect on epileptiform EEG activity or seizure control but are often responsible for intermittent side-effects. Conversely diagnostic EEG and monitoring studies may be required to classify seizures as an aid to determining appropriate medication and may explain apparent resistance to therapy, due to pseudo-seizures, reflex or self-induced epilepsy. Finally a case is presented for combined pharmacological EEG and video-monitoring in the preliminary assessment of new AEDs in order to improve the design of subsequent clinical trials.

Anticonvulsants↗
PubMed1985

Monitoring at the Instituut voor Epilepsiebestrijding Meer en Bosch.

A requirement for intensive epilepsy monitoring arose from a demand for ictal EEG registration for diagnostic purposes and in the context of pharmacokinetic research. The monitoring facility developed gradually: first conventional EEG equipment was used on the wards, later miniaturized pre-amplifiers were introduced to allow the patient greater freedom, finally a comprehensive specialized monitoring facility was created with its own accommodation. For most clinical and research applications arising in the Institute intensive observation and video monitoring are necessary. The greater reliability, channel capacity and bandwidth of cable telemetry offer considerable advantages over alternative monitoring techniques as radio telemetry. For recording from patients in locations outside the monitoring unit but where restricted mobility is acceptable a combination of telephone telemetry with a local radio link is used. Synchronization of EEG and video images is achieved by various means, depending on the application: split-screen technique, superimposition of EEG on video images or annotating the paper EEG chart with digital time information derived from the video time-date generator. Buffering of EEG signals is also available by means of a computer disk or a shift register. During the development of the system evaluation studies have been performed showing a progressively increasing yield of clinically useful information. At the most recent assessment, 79% of the investigations answered the clinical question addressed, in 65% of instances the findings had consequences for management and in over 25% the decisions resulting from monitoring had long-term therapeutic benefits for the patient.

Automation↗
PubMed1984

Temporal characteristics of seizures and epileptiform discharges.

The time relations of epileptic events have been studied in 3 sets of data: (I) counts of individual epileptiform discharges in twelve 48 h EEG recordings, (IIa) seizure calendars of 30 therapy-resistant outpatients participating in a drug trial, (IIb) seizure calendars of 10 mentally subnormal epileptic patients resident in a long-stay unit. The EEG data I were characterized most often by a Poisson distribution of intervals between discharges and the occurrence of marked periodicities, particularly at night. The periods of rhythmic nocturnal events ranged from 13 to 142 min and did not appear to correspond to the REM/non-REM cycle. In the seizure data IIa and b a Poisson distribution of intervals between events was found in half the patients. Periodicities occurred only in group IIa and did not correspond to weekly or monthly cycles. A stochastic process is considered to be the model which best fits these data.

Adolescent↗
PubMed1984

Colour and photosensitive epilepsy.

Red-coloured flicker is claimed to be more epileptogenic than white or that of other colours matched for subjective intensity. A feature of the colour opponent system is that the response of luminosity-sensitive cortical units to stimulation of ganglion cells of a particular spectral sensitivity is reduced when cells of other sensitivities are simultaneously stimulated. We hypothesized that the apparent effect of colour on photosensitivity was not a property of red light per se but arose simply from the fact that, with commercially available filters a light can be provided to stimulate only red sensitive cones, but owing to the overlap of the absorption spectra of the visual pigments it is difficult to stimulate only green or blue sensitive cones. Such stimulation of a single cone population can be achieved by the 'silent substitution method' which has been used for evoked response studies. In 12 photosensitive epileptic patients we find that, using stimulus intensities (less than 20 nits) at which white flicker is without effect, stimulation of either red or green cones by the silent substitution method may produce epileptiform discharges, there being a slight (and not significant) excess of patients showing a greater sensitivity for green than for red cone stimulation. The findings are considered to support the hypothesis set out above.

Color Perception↗
PubMed1984

The circadian distribution of interictal epileptiform EEG activity.

Eighteen continuous 48 h monitoring studies are reported from 17 patients with epilepsy. The numbers of epileptiform discharges over corresponding epochs of the 2 days were significantly positively correlated in 16 studies. However, this was explicable by masking due to the sleep/wake cycle and when waking and sleep were considered separately a minority of studies showed significant correlations. The difference in total 24 h production of discharges between the 2 days ranged from 1.3 to 30.3%, mean 15.1%. The maximum discharge rate in 75% of the studies occurred during sleep; during waking the distribution of discharges was random. Even in the waking state the 0.5 h discharge rate was extremely variable and in few patients could a single 30 min epoch be regarded as a reliable sample of the mean rate over the waking day. The intervals between events showed a Poisson distribution during 9 days and 5 nights, but there was no within-patient consistency between the first and second 24 h period. The occurrence of discharges was periodic significantly more often at night than during the day, but the periodicities did not clearly correspond to the REM cycle. Discharges increased overall during sleep in 14 studies, were unchanged in 2 and decreased in 4. The time of occurrence of maximal discharge rate during sleep was consistent from night I to night II only in patients exhibiting generalized regular spike-wave activity but random in the others. A negative correlation between antiepileptic drug levels and discharge rate was rarely observed.

Adult↗
PubMed1984

Selective cognitive impairment during focal and generalized epileptiform EEG activity.

It is well established that generalized epileptiform EEG discharges unaccompanied by overt clinical change may nevertheless be associated with transitory cognitive impairment (TCI) detectable by appropriate psychological testing. However, the tests employed in most research studies of this phenomenon are of little use for routine clinical application. They are suitable for administration only over short periods of time and are therefore applicable only to patients with a high discharge rate, a serious limitation, as the discharges are generally depressed by the tests themselves. We have developed two short-term memory tasks, one using verbal, the other nonverbal material presented in the form of television games which patients are generally prepared to perform for up to an hour or longer. Forty-six patients with subclinical EEG discharges have been studied. They were screened by video monitoring before and during testing to exclude any with overt clinical changes during the discharges. Despite this rigorous selection, in 50 per cent TCI was demonstrable with a confidence level (within the individual patient) of 10 per cent. Discharges during stimulus presentation were most disruptive of performance and those confined to the period when the patient was responding were without demonstrable effect. A significant association was found between the laterality of focal or asymmetrical generalized discharges and impairment of one or other task, left-sided discharges being associated with errors in the verbal task and right-sided with impairment of the nonverbal test. Two case histories are cited illustrating patients who were clearly handicapped by TCI and whose functioning improved when the subclinical discharges were suppressed by medication. To determine how many patients suffer such disabilities or can be helped by appropriate medication, further prospective studies are required.

Adolescent↗
PubMed1984

Epileptic nystagmus.

"Epileptic nystagmus" unaccompanied by other ictal phenomena is rare. We report four new cases confirmed by ictal EEG and video or cine recording in which nystagmus was a prominent and sometimes the only clinical manifestation of the seizures. The ictal EEG showed a parietal focus in three instances and generalized spike-wave activity in one.

Adolescent↗
PubMed1984

Double-blind placebo-controlled trial of flunarizine as add-on therapy in epilepsy.

In a therapy-resistant epileptic population with partial complex seizures with or without secondary generalization, addition of flunarizine to existing therapy was accompanied by a significant reduction in complex partial and tonic-clonic seizures. This result did not appear to be due to serial effects or changes in the plasma levels of the co-medication. Side effects were rare. The serum flunarizine levels (13.8 ng/ml; range, 3-32.5 ng/ml) were lower than previously reported on a daily dose of 10 mg. This may reflect increased metabolism due to induction of liver enzymes by the co-medication. Given this finding, together with the low incidence of side effects, a further study is required to determine whether higher blood levels would give an improved degree and incidence of seizure reduction.

Adolescent↗
PubMed1983

The effect of sleep deprivation on the EEG in epilepsy.

Many published studies report an increased incidence of epileptiform EEG activity following sleep deprivation in persons with epilepsy in whom a previous routine EEG was normal or inconclusive. Few such studies, however, permit a clear distinction to be made between the effects of sleep deprivation per se, sleep induction following deprivation, or simply repeated EEG recording. Sixty-nine patients have been investigated in whom a routine waking record, a secobarbital-induced sleep recording and an EEG following 24 h sleep deprivation were obtained in random order irrespective of whether or not the initial EEG contained epileptiform activity. For each record the incidence of epileptiform activity if any, was quantified in terms of discharges per minute for wake, drowsiness and each sleep stage. The findings confirmed the marked activating effect of light sleep on the EEG but there was no evidence of an overall increase in discharge rate after sleep deprivation either in the waking state or in the various sleep stages when these were compared with secobarbital-induced or spontaneous sleep. There was a significant increase of generalized discharges in the waking state only, after sleep deprivation, but a decrease in incidence of focal epileptiform activity. It is concluded that although specific indications may exist for the use of sleep deprivation, as a general method of EEG activation in epilepsy it has no advantages over barbiturate-induced sleep to offset the greater inconvenience to patients.

Adult↗
PubMed1982

Practical considerations in the positioning of EEG electrodes.

Although the 10-20 system of the International Federation was originally proposed as a basis for discussion, there has been little published comment on its strengths and weaknesses or suggestions for its improvement. There are inherent ambiguities in the system, which cannot be applied strictly in accordance with the published specification unless the 4 measurements between the right and left preauricular points and the nasion and the inion are all equal. A study of the cranial measurements of 20 normal adults showed that this criterion was fulfilled to within a margin of 10% in less than half. Further, the standard placements of the 10-20 system cover less than 3/4 of the cerebral convexity. A study of fronto-temporal epileptiform phenomena in 100 subjects indicated that in the majority these were of maximum amplitude over the anterior temporal region, some 20 mm below the typical positions of F7 and F8. In the light of these and previous studies, modifications of the 10-20 system are suggested.

Adult↗