Electroencephalography and Clinical Neurophysiology

Frequency-following responses (FFRs) to a low-frequency stimulus in 16 normal-hearing human subjects were cross-correlated with the stimulus in an attempt to yield more easily recognizable FFRs at lower intensity levels and increase threshold sensitivity. Cross-correlation of these responses with the stimulus did not improve threshold sensitivity and latencies obtained from the cross-correlated FFRs showed more variability and were uniformly shorter than those of standard FFR measurement.

One night's sleep loss in young adults increased delta (0.3-3 Hz) EEG only in the first non-REM period of recovery sleep. The delta increase was limited to frequencies 0.3-4 Hz; within this range, the effects on wave form periods and amplitudes differed by frequency band. These results illustrate the value of computer analysis applied to the physiological units of sleep (the successive non-REM and REM periods of each sleep cycle). The finding that all of the delta increase occurred in the first sleep cycle appears inconsistent with the exponential decline of delta across cycles predicted by 'recovery' models of sleep. The fact that wave periods and amplitudes are differentially affected by sleep loss indicates that it is premature to adopt any single wave form characteristic (e.g., power spectral density) to index delta sleep. Our data also confirm a recent report that eye movement density decreases after sleep loss; we hypothesize that this change results from greater depth of sleep; an inverse relation of depth of sleep to eye movement density provides a coherent explanation for a range of otherwise disparate observations. Lastly, we propose a new hypothesis to account for the presence of eye movement during REM sleep.

Twenty-eight healthy infants, split into 3 groups according to age (group 1: 2-6 weeks, n = 10; group 2: 7-14 weeks, n = 10; and group 3: 4-12 months, n = 8), were recorded during the whole night. For each infant, the longest quiet sleep (QS) phase occurring between 8 p.m. and midnight was selected for EEG power spectral analysis. The power in the frequency band related to low-frequency delta waves (0.5-1.5 Hz, "delta band") and the power in the frequency band related to sigma spindles (11.5-15.5 Hz, "sigma band") were analyzed. Group 1 infants showed no significant modification of the power in the sigma band in the course of the QS phase; the power in the delta band showed a significant increase between the second and the third 5 min segment and a decrease thereafter. Group 2 infants showed a progressive reduction of the power in the sigma band, whereas the power in the delta band increased during the first 15 min. In group 3 infants, the sigma band power significantly decreased between the third and the fifth 5 min segment without further changes. The power in the delta band, on the contrary, increased progressively for the first 20 min and showed a second progressive increase beyond 35 min. For both group 2 and group 3 infants, it appeared that the change in delta power preceded the change in sigma power. The above results provide quantitative evidence that a well-defined temporal inhomogeneity pattern in the EEG of the QS phase may appear between 7 and 14 weeks of age and continues from the fourth month on.

A computer program (PANV35) for modified period and amplitude analysis of the sleep EEG is described. This analysis requires prior visual classification of the polygraph record into REM, NREM and waking. Analysis of magnetic tape segments corresponding to NREM sleep is then carried out on a small digital computer. Baseline crossings, wave durations, integrated amplitude and curve length are obtained for specifiable frequency bands. These data are then processed on an IBM 360 system; a number of secondary measures are computed and the data are presented for all NREM sleep, by NREMPs, and for the average 20-sec NREM epoch. PANV35 was employed to analyze delta (0.5-3 c/sec) activity in NREM sleep in 20 young normal males aged 18-22.5 years, half of whom were long-distance runners in training. Measurement was carried out on 2 successive nights of recording which followed one adaptation night. Visually obtained sleep stage scores were also presented. Computer measures of delta showed excellent night-to-night reliability. Internight correlations for mean frequency within 0.5-3 c/sec were exceptionally high, indicating that this measure is an extremely stable individual characteristic. All delta measures showed highly reliable (P < 0.001) linear trends across NREM periods. Stage 4 showed a significant negative correlation with age. Computer analysis revealed that this change in visually scored delta was associated with a variety of alterations in 0.5-3 c/sec activity: amplitude, total duration, number and density of delta waves declined significantly with age and mean frequency increased. These findings indicate that period and amplitude analysis of NREM sleep yields measures which are both sensitive and stable.

The effect of traction injury to the eighth nerve on the compound action potentials (CAPs) recorded from the exposed nerve in response to tonebursts and click sounds was compared to responses elicited by continuous tones and noise that were amplitude-modulated with pseudorandom noise. Responses to the continuous sounds were presented in the form of cross-correlograms between the averaged response, with the averager locked to the periodicity of the noise and one period of the noise. While the wave form of these cross-correlograms was similar to the wave form of the response to the same, but unmodulated, stimulus when presented in short bursts when the nerve was intact, these two measures changed in different ways as a result of slight injury to the nerve. Thus, the N1 peak of the CAP in response to clicks and tones or noisebursts became prolonged when the nerve was stretched, while the first peak in the cross-correlograms was essentially unchanged. The second peak in the cross-correlogram was obliterated, but the N2 peak in the CAP was clearly present, although attenuated. More severe injury resulting in a nearly total conduction block, however, produced similar changes in the CAPs and cross-correlograms.

On account of the conflicting data concerning the action of 5-HTP on human sleep, repeated high doses were administered to three healthy subjects. The paradoxical sleep time and percentage tend to show a decrease during the 2nd week of treatment, followed by a rebound effect after the end of the treatment. In two subjects who initially had a small amount of slow wave sleep (SWS), the treatment induced an increase in SWS that persisted after the end of the treatment. Similar results were obtained after administration of 5-HTP together with RO.04.4602.

In rats deeply anaesthetized with urethane, injection of 1,2 dihydroxybenzene (catechol; 60 mg/kg i.p.) produces a stimulus-sensitive state in which a variety of sensory stimuli, e.g., a brief electrical shock or mechanical tap applied to the periphery, or a binaural click, produce brief (myoclonic) muscular jerks. These jerks have been recorded electromyographically in the forelimb from the biceps and triceps brachii and in the hind limb from gastrocnemius and tibialis anterior. The myoclonic jerks produced in these muscles by electrical or mechanical stimulation of the corresponding paw consisted of three distinct components. The early, first response to electrical stimulation has a short consistent latency (4.3 ± 0.6 msec in the forelimb; 8.1 ± 0.9 msec in the hind limb), large amplitude and high probability of occurence. This first response represents a polysynaptic reflex elicited by stimulation of cutaneous afferents. It is not, however, a simple reflex since it could be recorded in direct antagonists at a similar latency. The first response persisted in the hind limb muscles with both chronic and acute spinal transection at T10-T12. The second response (13.4 ± 1.6 msec in the forelimb; 19.4 ± 3.7 msec in the hind limb) and the third response (40.0 ± 7.3 msec and 51.4 ± 7.3 msec respectively) were both abolished in the hind limb muscles by spinal transection. Records of single motor units in the tibial nerve showed that discharge of a single motoneurone can account for all three components of the reflex jerk. The second, and to a lesser extent, the third response were always reduced in amplitude when the first response was large. Conversely, large second responses were only recorded when the first response was small or absent. Catechol had no effect on the amplitude or latency of the afferent volley recorded at the dorsal root entry zone, but markedly potentiated both mono- and polysynaptic reflexes.

1. 1. Intravenous or intraperitoneal injection of 1,2-dihydroxybenzene in deeply anaesthetized animals produces a net increase in the excitability of the dorsal column sensory pathway. The effect lasts for 10 min or more, depending upon the dose administered and the route of administration. 2. 2. Responses recorded from the primary somatic cortical receiving area and ventro-basal thalamus, to peripheral stimulation, increase in size and show a reduction in the scatter of both size and latency of the individual responses. 3. 3. Responses recorded from the cuneate nucleus show either no change in their size or temporal pattern or, in some cases, a size reduction. 4. 4. These changes are accompanied by generalized EEG "arousal", increased respiratory effort and changes in the discharge frequencies of cells located in the thalamus outside the dorsal column sensory pathway: in the nucleus reticularis thalami and the nucleus ventralis pars dorsomedialis. 5. 5. It is proposed that the initial increase in excitability is due to an increased responsiveness of the cerebral cortex to a thalamo-cortical volley consequent upon the hypernoea produced by the 1,2-dihydroxybenzene. The continuing increase is due to an increased responsiveness of the ventro-basal thalamus brought about by the modulatory influence of the thalamic reticular nuclei. During this latter period the cortical responsiveness to electrical stimulation of the thalamo-cortical fibres is unaltered or decreased.

A study has been made of the convulsive activity produced by 1,2-dihydroxybenzene (catechol) in the deeply anaesthetized rat. "Spontaneous" convulsions (which occurred in the absence of any intentional external stimulus) consisted of a series of brief muscle twitches all over the body, either asynchronously or progressively spreading from the head to the trunk and limbs. This convulsive activity has been quantitatively assessed by recording the frequency and integrated tension of the jerks in extensors and flexors of the fore- and hind limbs. In any one animal, responses of similar intensity and duration were produced by successive doses of catechol (60 mg/kg i.p.) at hourly intervals, providing the body temperature was kept constant. The convulsions were abolished by denervation of the appropriate muscles or by destruction of the spinal cord. Convulsive activity in the hind limb muscles was greatly reduced but not extinguished by both chronic and acute spinal transection at the thoracic level. The convulsions were enhanced in extensor muscles by removal of those areas of the brain known to activate the brain-stem reticulo-spinal inhibitory system. At the same time convulsive activity in flexor muscles was markedly reduced. These observations, together with the initial increase in rigidity seen in unanaesthetized decerebrate rats given catechol and the almost total abolition of convulsive activity in animals subjected to dorsal root section, imply that catechol exerts its effect via the gamma system by action on the brain-stem reticulo-spinal system.

6-Azauracil, a new experimental anti-tumor agent, has been given to 19 patients. In 17, it has induced significant electroencephalographic and neurologic changes. EEG changes have consisted of: abolition of the fast rhythms; disorganization of the background activity with moderate amplitude, irregular slowing; depression or disappearance of the response to photic stimulation; and appearance of high amplitude delta rhythm. Clinically, the most striking change has been lethargy progressing to subcoma. The discrepancy between the electrographic changes and the clinical abnormalities has been striking, the electrographic abnormalities generally appearing considerably before those detectable clinically. All manifestations induced by the 6-Azauracil have regressed when the drug was discontinued. The changes induced were directly related to the dosage of the drug employed. Children appeared more susceptible than adults to its toxic manifestations. Its mode and site of action are unknown.

This report is intended to complement the current body of literature by describing pattern reversal evoked potential (PREP) component amplitudes and latencies in a larger sample than has been previously studied and providing comparisons of males and females across the lifespan. Binocular PREPs were measured from 406 normal subjects, 6-80 years of age. In general, latencies were found to decrease during maturation, stabilize across early adulthood, then begin to increase sometime after the late 20s. There were minimal gender differences in latencies during development but males tended to have longer latencies than females during adulthood. Across the lifespan, amplitudes were larger for females. Results of regression analyses using the entire data set were compared to results of separate regression analyses for developmental years (6-20) and adulthood (21-80). Separate analyses appear to provide more useful descriptions of PREP latency and amplitude changes across the lifespan. It is clear that predicted normal values can vary depending on age range and relative proportion of males and females comprising a reference sample. Appropriate clinical values should be based on age- and sex-matched normal subjects and should be specific with regard to technical and methodological variables.

A prospective analysis of 40 patients with hypoxic-ischemic coma lasting at least 6 h following sudden cardiac arrest was undertaken. The patients, all of whom had preserved brain-stem function, were studied electrophysiologically with electroencephalography (EEG), and median nerve somatosensory evoked potentials (SEPs) within 48 h to establish prognostic indices. Our results indicate that preserved brain-stem function does not necessarily predict favorable outcome following cardiac arrest as 26 of 40 (65%) patients died without awakening. The bilateral absence of cortical evoked potentials predicted death without awakening in 19 of 26 patients (73%) while malignant EEG change was similarly predictive in 11 patients (42%). Bilateral absence of cortical evoked potentials and/or malignant EEG change reliably predicted unfavorable outcome in 21/26 patients (81%). Patients with normal or delayed central conduction time (CCT) as well as 'benign' or 'uncertain' EEG findings had an uncertain prognosis as some entered a persistent vegetative state (PVS) or died without awakening. Fourteen patients (35%) awakened of whom 5 (13%) recovered completely while another 9 (23%) had varying degrees of motor or cognitive impairment. SEP and EEG findings did not distinguish between these outcomes.

A 20 msec train (500 Hz; 0.1-0.2 msec duration) of percutaneous electrical stimulation (ES) applied to the plantar surface was used to condition muscle responses evoked in tibialis anterior (TA) by transcranial magnetic stimulation of the motor cortex in 8 subjects with traumatic spinal cord injury (SCI). The intensity of conditioning ES was adjusted to just subthreshold for evoking flexion reflexes in TA and was delivered at conditioning-test (C-T) intervals of 15-60 msec prior to cortical stimulation. Four subjects with clinically complete SCI revealed no muscle response to cortical stimulation or following combined subliminal percutaneous ES and cortical stimulation. Four subjects (3 clinically incomplete and 1 complete injury) demonstrated muscle responses with a latency of 70-80 msec time-locked to the percutaneous ES when the conditioning subliminal stimulation was delivered at C-T: 15-40 msec. These responses, resembling suprathreshold flexion reflexes, reflect the convergence of excitatory afferent and cortical inputs and provide evidence of preserved corticospinal innervation to the L4-5 segmental motoneuron or interneuron pools. In 3 of the subjects this preserved corticospinal influence was evident despite absence of motor evoked potentials (MEPs) following cortical stimulation. The effect of the combined electrical and cortical stimulation in yielding suprathreshold flexion reflexes, instead of the facilitated MEPs seen in control subjects, appears to be related to slowed central conduction, prolonged temporal dispersion of the motoneuron facilitation following cortical stimulation and segmental reflex changes associated with disrupted modulation of interneuronal pathways. The results show this conditioning paradigm to be useful in revealing preserved corticospinal innervation in some SCI subjects with absent MEPs.

Focal transcranial magnetic stimulation (TCS) was employed for the representation of the motor cortex in a population of 18 patients to investigate the functional properties of hand motor areas 2-4 months after a monohemispheric stroke. Eleven sites were stimulated to elicit motor evoked potentials (MEPs) in abductor digiti minimi muscle after TCS of affected (AH) and unaffected (UH) hemispheres; recording sessions were performed at the beginning (T1) and after 8-10 weeks (T2) of neurorehabilitation. Barthel index and Canadian neurological scale scores were evaluated. A group of 20 healthy control subjects was enrolled. In stroke patients the AH was less excitable than normal, combined with a decrease in motor cortical output area (P < 0.05) in T1. In T2, there was an enlargement of the hand motor area on the AH combined with an improvement of clinical scores (P < 0.001). In T1 and T2, the amplitude of MEPs in the AH was reduced (P < 0.001) with a prolongation of central conduction time (P < 0.001) and with a tendency towards improvement in T2; the amplitude of contracted MEPs was larger than normal in the UH in T1. Both in T1 and T2, anomalous 'hot spot' (most excitable) scalp sites, never seen in normals, were often encountered (T2 > T1) on the AH and UH. Interhemispheric differences for topography and latency of MEPs were remarkably affected. Our data are consistent with a rearrangement of the brain motor cortical output between 2 and 4 months following stroke. The amelioration of the neurophysiological parameters was correlated with clinical improvement in disability and neurological scores. This study confirms the existence in adults of brain 'plasticity' still operating between 2 and 4 months from an acute vascular monohemispheric insult.

MANOVA and repeated measures ANOVA approaches have provided evidence of a number of limitations in several event-related potential (ERP) studies due to violations of their statistical assumptions and the typically moderate size of the available sample. Alternative, computer-intensive methods based on permutation principles have recently been developed. Up to now this methodology has focused mostly on magnitude differences between scalp distributions as measured by t statistics. In this paper the scope of permutation techniques in ERP analysis was widened. A new statistic (D statistic) is introduced to compare the shapes of scalp distributions of ERPs. Additionally a general non-parametric combinatory technique is introduced to evaluate, by means of multivariate permutation tests, several time points and/or recording sites in ERP data. The methodology described here was used to test if two ERP components elicited during word-pair matching tasks to semantic or phonological incongruences had different scalp distributions.

In the present study, the component structure of auditory event-related potentials (ERP) was studied in children of 7-9 years old by presenting stimuli with different interstimulus intervals (ISI). A short-term auditory sensory memory, as reflected by ISI effects on ERPs, was also studied. Auditory ERPs were recorded to brief unattended 1000 Hz frequent, 'standard' and 1100 Hz rare, 'deviant' (probability 0.1) tone stimuli with ISIs of 350, 700 and 1400 ms (in separate blocks). With the 350 ms-ISI, the ERP waveform to the standard stimulus consisted of P100-N250 peaks. With the two longer ISIs, in addition, the frontocentral N160 and N460 peaks were observed. Results suggested that N160, found with the longer ISIs, is a correlate of the adult auditory N1. In difference waves, obtained by subtracting ERP to standard stimuli from ERP to deviant stimuli, two negativities were revealed. The first was the mismatch negativity (MMN), which is elicited by any discriminable change in repetitive auditory input. The MMN data suggested that neural traces of auditory sensory memory lasted for at least 1400 ms, probably considerably longer, as no MMN attenuation was found across the ISIs used. The second, later negativity was similar to MMN in all aspects, except for the scalp distribution, which was posterior to that of the MMN.

The visual evoked response to a 7 mm (40') check using a pattern reversal stimulus was measured in 73 normal children, aged 6-11. Full pattern displacement for the right and left eye and 1/4 and 1/2 pattern displacement for the right eye were studied. The amplitudes of the N65-P95 and P95-N125 wave, together with the P95 latency, were measured. Analysis of the data showed that there was no clear relationship between the mean amplitude or latency of the evoked response and age. However, significant changes were found between linear displacement and linear age for the N65-P95 wave and there was a complex interaction for the same wave between age, sex and eye. There was a significant difference in latencies between right and left eye between the boys and the girls, with the boys having longer latencies. There are thus both age- and sex-related differences in the amplitude and latency of the N65-P95 wave in 6-11 year-old children.

In a longitudinal study a selective attention task was administered to 11-13-year-old children. During this task (employing a combined filter and selective-set paradigm), event-related brain potentials were recorded to study timing and morphology of early and late selection processes. Task performance was prospectively and retrospectively related to neurological optimality at birth and to flash-evoked potential correlates that were registered at the age of five. The results provided evidence that even after 13 years neonatal neurological suboptimality was reflected in task performance, both in reaction time and in electrophysiological data. Task load interacted with group classification according to optimality to the disadvantage of suboptimals. This implied that load demands differentiated between groups. The event-related brain potentials revealed the existence of a negative shift associated with memory load (search-related negativity) at Fz and Cz, and a positive deflection at Pz (P3b) associated with target detection. Cortical activity, expressed in terms of these deflections, appeared to be less pronounced for the suboptimal group.

Neurogenic motor evoked potential (NMEP) monitoring, which basically represents a monitoring of both motor and somatosensory tracts, has been proposed as a warning system in preventing neural damage during spinal surgery. The aim of this study was to report our clinical experience in 112 consecutive patients undergoing surgery for spinal deformity, and to emphasize the interest of NMEP monitoring. NMEPs were elicited in each patient by electrical stimulation of the spinal cord via needle electrodes placed by the surgeon in the rostral part of the surgical field, and recorded from the right and left sciatic nerves. Concomitantly, somatosensory evoked potentials (SSEPs) were obtained using a standard method. No false-negative cases of intra-operative spinal cord damage were reported. In 3 patients, both NMEPs and SSEPs suddenly disappeared during specific surgical manipulations of the vertebral implants. In these patients, the level of the lesion was easily recognized by moving the stimulating electrodes of NMEPs along the spinal cord, allowing the surgeon to perform laminectomy at the appropriate vertebral level. Spinal cord decompression was a success in two patients, the last unfortunately being paraplegic. Two additional patients exhibited transient reduction in NMEP amplitude at the insertion of a rod while SSEPs did not change significantly. In these two cases, the surgeon modified his procedure according to the NMEP changes, possibly avoiding a neurological complication. Each time evoked potentials were significantly altered, significant information was more rapidly acquired with NMEPs than with SSEPs. These results suggest that NMEPs can be used as primary choice for detecting impeding lesion of the spinal cord during critical steps of spinal surgery.

The temperature of electrodes and metal disks positioned close to a coil was measured during rapid-rate magnetic stimulation. The temperature rise ranged from a fraction of a degree to almost half a degree per stimulus pulse and increased with the electrical conductivity of the metal, the square of the electrode radius and the square of the stimulus strength, and was independent of the electrode thickness. During a brief high-frequency train, the temperature increase from each pulse added; during a long, high-frequency train the temperature increase approached a steady state. After the stimulus ended, an electrode on the arm cooled with a time constant of about 45 sec. A standard silver EEG electrode on the surface of the skin did not increase in temperature enough to induce a skin burn if the stimulating rate was below 0.4 Hz or the total number of stimuli was less than 20. Heating was reduced by cutting gaps in the electrode.

Visual evoked cortical potentials and related EEG activity were recorded from subjects during rapid compression and exposure to pressures of 400, 800, 1200 and 1600 fsw. In one phase, subjects made repeated excursions to 1200 fsw from a base at 800 fsw; in the second phase, the saturated base was 1200 fsw with excursions to 1600 fsw. The results included: (1) For the visual evoked potentials, sizeable and significant decreases in amplitude and increases in latency of the response with depth; (2) Changes in the visual evoked potentials which varied systematically with depth but not with related changes in compression rate or decompression. The changes were small but consistent alterations of normal responses to visual stimulation; and (3) Theta activity in discrete EEG recordings increased progressively with depth. With all subjects showed increases in theta activity the pattern of increase varied individually.

The frequency and characteristics of P14 abnormalities were investigated in 122 patients with probable (68), or definite (54) multiple sclerosis by recording SEPs to median nerve stimulation with a non-cephalic reference montage. The most frequent SEP abnormality found in our series (62% of abnormal results) combined latency increase and amplitude reduction of P14. Interindividual variability, inherent in absolute amplitude measurements, was by-passed by calculating the ratio between the amplitudes of far-field P9 and P14 components, which proved to be normally distributed in controls. In spite of the strong association (P much less than 0.001) between the P9-P14 interpeak interval (IPL) and the P9/P14 amplitude ratio in MS patients, the latter parameter was found to be the only abnormality in 12 patients whose P9-P14 and P14-N20 IPLs were normal. Also IPLs were increased in 12 patients with normal P14 amplitudes. These results suggest that adding the P9/P14 amplitude criterion to standard IPL data might be useful to detect conduction troubles in MS patients.

This paper describes a method for increasing the spatial detail of the EEG and for integrating physiological data with anatomical models based on magnetic resonance images (MRIs). This method includes techniques to efficiently record EEG data from up to 124 channels, to measure 3-D electrode positions for alignment with MRI-derived head models, and to estimate potentials near the outer convexity of the cortex using a spatial deblurring technique which uses a realistic model of the structure of the head and which makes no assumptions about the number or type of generator sources. The validity of this approach has been initially tested by comparing estimated cortical potentials with those measured with subdural grid recordings from two neurosurgical patients. The method is illustrated with somatosensory steady-state evoked potential data recorded from 5 healthy subjects. Results suggest that deblurred 124-channel topographic maps, registered with a subject's MRI and rendered in 3 dimensions, provide better spatial detail than has heretofore been obtained with scalp EEG recordings. The results also suggest that the potential for EEG as a functional neuroimaging modality has yet to be fully realized.

Cranial computerized tomography (CCT) in permitting visualization of cerebral edema in live patients, allows for the first time valid studies concerning the role of reactional edema in the generation of EEG abnormalities related to expanding processes. The authors analyze the results of EEG and CCT in 127 patients presenting cerebral tumor(s), 84 of which were accompanied by reactional edema. The study leads to the conclusion (also demonstrated by certain animal work) that edema per se is only rarely responsible (9.5%) for the EEG abnormalities.

A 128-channel cable-telemetry EEG monitoring system has been developed for use on patients undergoing intensive neurodiagnostic monitoring with invasive intracranial electrodes. A unique head mounted preamplifier/multiplexor design allows continuous recording from any combination of intracerebral, subdural, epidural or surface electrodes. A computer is used to delay or buffer all 128 channels by 2 min or more. This computer is connected to a fileserver via a local area network and is used exclusively for data acquisition. Seizure files created by the activation of the seizure/event push button or detected by a second computer containing on-line seizure/spike detection algorithms are written directly on to the fileserver by the acquisition computer. The 128 channels of EEG recorded on the fileserver can then be remotely reviewed on a high resolution graphics terminal, printed out on a laser jet printer, archived or played out on paper, 16 channels at a time on any EEG machine. A time of day signal is also generated by the computer to permit time correlation with a continuous audio/video VCR unit which permits comparison of the EEG and clinical events. This system allows continuous EEG monitoring of extensive multichannel arrays not previously possible with conventional 16-, 32- or even 64-channel systems.

Contingent negative variations (CNVs) and Bereitschaftspotentials (BPs) were recorded from subdural electrodes implanted in 14 patients with intractable epilepsy. For recording CNVs, a Go/NoGo S2 choice reaction-time paradigm was employed. Two seconds after presentation of a low tone burst (S1), either a medium (S2m) or a high tone burst (S2h) was delivered at random. Patients were instructed to make middle finger extensions after S2m but not after S2h. For recording BPs, patients repeated self-paced middle finger extensions. BPs were recorded from the primary motor area (MI), the primary sensory area (SI) and the supplementary sensorimotor area (SSMA). CNVs showed a patchy distribution in the prefrontal area and SSMA for the early component and in the prefrontal area, MI, SI, temporal area, occipital area and SSMA for the late component. These results suggest that the CNV recorded from the scalp is the summation of multiple cortical potentials which have different origins and different functions. The cortical distribution of the late CNVs was different from that of BPs. Late CNVs are not equivalent to BPs and are not related to motor preparation alone. After S2, 3 kinds of potentials, probably related to decision making, somatosensory feedback and motor execution under specific conditions, respectively, were observed.

Good reliability was found in EEG spectra recorded during resting conditions in two studies 1-3 years apart in groups of adolescent dyslexic and control boys who were well screened for neurological, sensory and emotional disabilities. The studies used different equipment and analysis (FFT in study 1 vs. iterative digital bandpass filters in study 2). The central leads (C3 and C4) referenced to vertex were recorded in both studies. Pearson correlation coefficients were computed as reliability estimates for each spectral band separately for each group, for absolute and relative power and for eyes open and eyes closed recording conditions. For both groups and for all conditions, the absolute power reliabilities were above 0.71 for all bands except delta for which they were above 0.54. Reliabilities were more variable for relative power measures.

Posturography was performed in 41 patients with cerebellar diseases by means of a force measuring platform using an on-line computer program which calculated sway path, sway area, antero-posterior and lateral sway components and the amount of visual stabilization. Postural ataxia was quantitatively studied in 8 patients with spinal ataxia (Friedreich's), 6 patients with vestibulocerebellar lesions, 11 patients with anterior lobe atrophy, 7 patients with hemispheral cerebellar lesions, and 9 patients with a disease affecting all parts of the cerebellum. Patients with lesions of the cerebellar hemispheres could not be separated from normals by means of posturography. Lesions of the spino-cerebellar afferents (Friedreich' ataxia) caused an omnidirectional low frequency sway with preserved visual stabilization. Patients with anterior lobe atrophy showed a predominant antero-posterior sway, often with a spontaneous high frequency body tremor around 3 Hz. Vestibulo-cerebellar lesions exhibited omnidirectional low frequency sway poorly stabilized by vision. Quantitative posturography helps to localize cerebellar lesions and allows for quantitative follow-up studies of cerebellar diseases.

14-and-6 Hz positive bursts, a benign epileptiform variant, have also been described in comatose children with liver disease, chiefly Reyes syndrome. To determine the incidence of this pattern in children in stupor or coma, 154 portable EEGs in 111 children with mental status changes were reviewed. Seven children showed 14-and-6 Hz bursts in the setting of moderate to marked background slowing. They were similar to positive bursts seen in normals in location, duration, morphology, frequency and repetition rate. They differed in being readily activated by stimulation. The etiology was toxic/metabolic in 4 cases, primary cerebral insult in 2 cases and a combination of the two in 1 case. Amongst an age-matched control population, 5 of 75 showed 14-and-6 Hz positive bursts in stage I or II sleep. There were no statistically significant differences in incidence rates between the 2 groups. 14-and-6 Hz positive bursts may occur in diverse encephalopathies of childhood, not just Reyes syndrome. The similar incidence rate, morphology and topography to normals suggest that the presence of these wave forms in encephalopathies represents persistence of a normal EEG feature rather than an expression of some underlying pathophysiological process.

1. 1. Adult cats were trained in a free operant paradigm to produce a synchronized pattern (12-14 c/sec) of sensorimotor or cortical activity in order to obtain a milk reward. 2. 2. Somatic and visceral motor functions were monitored before and during episodes of conditioned sensorimotor activity. 3. 3. During conditioned 12-14 c/sec activity, consistent patterns of motor phenomena were observed which included a cessation of movement and a depression of somatic motor activity. 4. 4. A shift in visceral motor processes toward levels of activity which were parasympathetic in nature occurred during 12-14 c/sec activity. Heart rate decreased, and the pattern of respiration became more regular than during control periods. The onset of a conditioned EEG episode was correlated with inspiration and its termination with expiration. 5. 5. The following hypotheses were suggested based upon the results presented in this paper: (a) the specific EEG patterns of sensory and motor cortical gyri are correlated with uniform and functionally adaptive variations in somatic and visceral motor activity; (b) patterns of synchronized activity may reflect localized sites of "idling" within cortical areas devoted to primary sensory functions; and (c) the processes or conditions underlying 12-14 c/sec activity of the sensorimotor cortex are analogous to those responsible for the alpha activity of the visual cortex.

We describe the unilateral occurrence of 14 and 6 Hz positive bursts in successive EEGs in a 25-year-old woman following surgical resection of a left parietal arteriovenous malformation which had caused a left parieto-temporal intracerebral hematoma. This is only the second reported case of unilateral 14 and 6 Hz positive bursts. This could represent either a normal pattern seen unilaterally because of a skull defect or be a manifestation of neuronal damage.

The sleep patterns of 8 normal subjects living in a winter-type photoperiod (10 h light and 14 h darkness; LD 10:14) for 4 weeks were characterized by the presence of periods of spontaneous wakefulness alternating with periods of spontaneous sleep. Transitions from sleep to wakefulness occurred much more frequently out of REM sleep than out of NREM sleep (P < 0.002). REM periods that terminated in wakefulness showed shorter REM durations (P < 0.0005) and higher REM densities (P < 0.0005) than REM periods that did not terminate in wakefulness. The authors discuss these results in terms of a possible relationship between REM density and arousal level. The higher REM density preceding wakefulness and the increased number of REM periods terminating in spontaneous awakenings could reflect an enhanced level of a brain arousing process, resulting from reduced sleep pressure in the extended nights.

Of sixty voluntarily hospitalized psychiatric patients 16–35 years of age, nine had 14 and 6/sec positive spiking. Of these nine patients, eight were diagnosed as schizophrenic. These eight comprised the positive spike group. They were matched for age, sex and diagnosis to an equal number of patients with normal EEGs; this was the control group. The positive spike group showed less affective relatedness, less sensitivity to others, less understanding of the consequences of their actions, more aggressive behavior, more suicidal risk, and presented more management problems than the normal EEG comparison groups.

A computer technique for the simultaneous averaging of epileptic discharges in 14 channels is presented.It is based on direct visual identification of reference points within the considered electric events and on the computation of their average using selected samples stored after A-D conversion.It can be utilized in studies concerned with the morphology of epileptic spikes and their temporal relationships among different leads.RésuméLes auteurs présentent une nouvelle technique d'évaluation simultanée de la moyenne des décharges épileptiques recueillies dans 14 dérivations.Elle est basée sur l'identification visuelle directe de points de référence à l'intériur du potentiel considéré et sur le calcul de la moyenne en utilisant les échantillons stockés après conversion A-D.Elle trouve son application dans les études relatives à la morphologie des pointes épileptiques et leurs rapports chronologiques, lorsqu'elles sont enregistrées sur différentes dérivations.

A 15 year old girl with a history of childhood absence seizures underwent a prolonged EEG recording. Twelve bursts of 3 Hz generalized spike and wave were recorded during drowsiness and light sleep, all of which were preceded by 14 and 6 Hz positive spikes with a latency of under 1 s. Nine bursts of polyspike-wave, not preceded by 14 and 6 Hz positive spikes, were recorded during deeper sleep (stage 3). The bursts of polyspike-wave were significantly longer when preceded by 14 and 6 Hz spikes than when observed in isolation. The close association between these paroxysmal events in our patient is intriguing, may be coincidental, and has never before been reported.

A case is described of a patient who exhibited positive bursts (14- and 6/sec positive spikes) in waking and sleep EEGs approximately 3.5 months after a penetrating wound to the brain. Pneumoencephalogram revealed the presence of a metallic fragment in the left thalamus which had presumably transversed the cortex, basal ganglia and thalamus on the right side and the third ventricle. Unusual features of this case included the precipitation of the paroxysms by eye closure in waking tracings.RésuméLes auteurs décrivent le cas d'un malade chez lequel on note des bouffées de pointes positives de 14 et 6/sec sur l'EEG de veille et de sommeil, environ 3,5 mois après plaie pénétrante du cerveau. Le pneumoencéphalogramme révèle la présence d'un fragment métallique dans le thalamus gauche, ayant probablement traversé le cortex, les ganglions de la base et le thalamus du côté droit, ainsi que le troisième ventricule. Ce cas présente des signes inhabituels parmi lesquels la facilitation des paroxysmes par fermeture des jeux sur les tracés de veille.

1.1. Eleven patients showing 14 and 6/sec positive spikes (14 and 6 PS) during routine EEG examination and with diphenhydramine activation were studied during nocturnal sleep. Two patients who showed this pattern only during nocturnal sleep and another four cases with bilateral synchronous 5–6/sec spike and wave paroxysms were also similarly studied. The incidence (per minute) of the 14 and 6 PS and the spike and wave paroxysms during different stages of sleep was calculated and the discharging patterns were classified into 4 types according to their preferential occurrence in one or the other stage.2.2. All the patients who showed 14 and 6 PS during routine EEG and diphenhydramine activation also exhibited this pattern during the nocturnal sleep recording.3.3. In more than half of the cases, 14 and 6 PS appeared most frequently during the stage 1-REM period and the incidence rates during the spindle phase were very low. The bilateral synchronous spike and wave paroxysm, on the other hand, tended to show high incidence during the waking state and stages 1, 2 and 3, and the incidence in the stage 1-REM was relatively low.4.4. It was assumed that the 14 and 6 PS were not associated with sleep spindles. It was also revealed that the discharging pattern of the 14 and 6 PS during nocturnal sleep was different from that of both the centrencephalic and focal cortical seizure discharges. The possible mechanisms of the enhancement of the 14 and 6 PS during stage 1-REM were discussed.