Somatosensory system evoked potentials during waking behavior and sleep in the cat

Neurofeedback for Tinnitus Treatment - Review and Current Concepts

An effective treatment to completely alleviate chronic tinnitus symptoms has not yet been discovered. However, recent developments suggest that neurofeedback (NFB), a method already popular in the treatment of other psychological and neurological disorders, may provide a suitable alternative. NFB is a non-invasive method generally based on electrophysiological recordings and visualizing of certain aspects of brain activity as positive or negative feedback that enables patients to voluntarily control their brain activity and thus triggers them to unlearn typical neural activity patterns related to tinnitus. The purpose of this review is to summarize and discuss previous findings of neurofeedback treatment studies in the field of chronic tinnitus. In doing so, also an overview about the underlying theories of tinnitus emergence is presented and results of resting-state EEG and MEG studies summarized and critically discussed. To date, neurofeedback as well as electrophysiological tinnitus studies lack general guidelines that are crucial to produce more comparable and consistent results. Even though neurofeedback has already shown promising results for chronic tinnitus treatment, further research is needed in order to develop more sophisticated protocols that are able to tackle the individual needs of tinnitus patients more specifically.

Expert-novice differences in SMR activity during dart throwing

Previous evidence suggests that augmented sensorimotor rhythm (SMR) activity is related to the superior regulation of processing cognitive-motor information in motor performance. However, no published studies have examined the relationship between SMR and performance in precision sports; thus, this study examined the relationship between SMR activity and the level of skilled performance in tasks requiring high levels of attention (e.g., dart throwing). We hypothesized that skilled performance would be associated with higher SMR activity. Fourteen dart-throwing experts and eleven novices were recruited. Participants were requested to perform 60 dart throws while EEG was recorded. The 2(Group: Expert, Novice)×2(Time window: -2000 ms to -1000 ms, -1000 ms to 0 ms) ANOVA showed that the dart-throwing experts maintained a relatively higher SMR power than the novices before dart release. These results suggest that SMR might reflect the adaptive regulation of cognitive-motor processing during the preparatory period.

Neurofeedback treatment of epilepsy: from basic rationale to practical application

The treatment of epilepsy through operant conditioning of the sensorimotor rhythm electroencephalogram has a 35-year history. Neurophysiological studies have shown that this phasic oscillation reflects an inhibitory state of the sensorimotor system. Operant learning of sensory motor rhythm production results in an upregulation of excitation thresholds within the thalamocortical sensory and motor circuitry, which in turn is associated with reduced susceptibility to seizures. The clinical benefits derived from this neurofeedback training protocol, particularly in patients that are nonresponsive to pharmacotherapy, have been documented in many independent laboratories. Recent advances in computer technology have resulted in the availability of relatively inexpensive high-quality equipment for the application of neurofeedback therapy, thus presenting a viable and promising treatment alternative to the interested clinician.

Mechanisms underlying state dependent surface-evoked response patterns

Cortical evoked response potentials (ERPs) display a rich set of waveforms that are both context and state dependent. However, the mechanisms that underlie state dependent ERP patterns are unclear. Determining those mechanisms through analysis of single trial ERP waveform signatures may provide insight into the regulation of cortical column state and the roles that sleep plays in cortical function. We implanted rats with electroencephalogram (EEG) and electromyogram (EMG) electrodes to record ERPs and to assess sleep/wake states continuously during 1-2 s random auditory clicks. Individual cortical auditory ERPs were sorted into one of eight behavioral states, and fell into three categories based on amplitude and latency characteristics. ERPs within waking and rapid eye movement (REM) sleep were predominantly low amplitude and short latency. Approximately 50% of ERPs during light quiet sleep (quiet sleep 1 and quiet sleep 2) exhibited low amplitude, short latency responses, and the remaining ERPs had high amplitude, long latency responses. This distribution was characteristic of EEG fluctuations during low frequency delta waves. Significantly more individual ERPs showed very low amplitudes during deep quiet sleep (quiet sleep 3 and quiet sleep 4), resulting in a lower average ERP. These results support the hypothesis that evoked response amplitudes and waveform patterns follow specific EEG patterns. Since evoked response characteristics distribute differently across states, they could aid our understanding of sleep mechanisms through state-related and local neural signaling.

Foundation and Practice of Neurofeedback for the Treatment of Epilepsy

This review provides an updated overview of the neurophysiological rationale, basic and clinical research literature, and current methods of practice pertaining to clinical neurofeedback. It is based on documented findings, rational theory, and the research and clinical experience of the authors. While considering general issues of physiology, learning principles, and methodology, it focuses on the treatment of epilepsy with sensorimotor rhythm (SMR) training, arguably the best established clinical application of EEG operant conditioning. The basic research literature provides ample data to support a very detailed model of the neural generation of SMR, as well as the most likely candidate mechanism underlying its efficacy in clinical treatment. Further, while more controlled clinical trials would be desirable, a respectable literature supports the clinical utility of this alternative treatment for epilepsy. However, the skilled practice of clinical neurofeedback requires a solid understanding of the neurophysiology underlying EEG oscillation, operant learning principles and mechanisms, as well as an in-depth appreciation of the ins and outs of the various hardware/software equipment options open to the practitioner. It is suggested that the best clinical practice includes the systematic mapping of quantitative multi-electrode EEG measures against a normative database before and after treatment to guide the choice of treatment strategy and document progress towards EEG normalization. We conclude that the research literature reviewed in this article justifies the assertion that neurofeedback treatment of epilepsy/seizure disorders constitutes a well-founded and viable alternative to anticonvulsant pharmacotherapy.

EEG slow (approximately 1 Hz) waves are associated with nonstationarity of thalamo-cortical sensory processing in the sleeping human

Intracellular studies reveal that, during slow wave sleep (SWS), the entire cortical network can swing rhythmically between extremely different microstates, ranging from wakefulness-like network activation to functional disconnection in the space of a few hundred milliseconds. This alternation of states also involves the thalamic neurons and is reflected in the EEG by a slow (<1 Hz) oscillation. These rhythmic changes, occurring in the thalamo-cortical circuits during SWS, may have relevant, phasic effects on the transmission and processing of sensory information. However, brain reactivity to sensory stimuli, during SWS, has traditionally been studied by means of sequential averaging, a procedure that necessarily masks any short-term fluctuation of responsiveness. The aim of this study was to provide a dynamic evaluation of brain reactivity to sensory stimuli in naturally sleeping humans. To this aim, single-trial somatosensory evoked potentials (SEPs) were grouped and averaged as a function of the phase of the ongoing sleep slow (<1 Hz) oscillation. This procedure revealed a dynamic profile of responsiveness, which was conditioned by the phase of the spontaneous sleep EEG. Overall, the amplitude of the evoked potential changed sistematically, increasing and approaching wakefulness levels along the negative slope of the EEG oscillation and decaying below SWS average levels along the positive drift. These marked and fast changes of stimulus-correlated electrical activity involved both short (N20) and long latency (P60 and P100) components of SEPs. In addition, the observed short-term response variability appeared to be centrally generated and specifically related to the evolution of the spontaneous oscillatory pattern. The present findings demonstrate that thalamo-cortical processing of sensory information is not stationary in the very short period (approximately 500 ms) during natural SWS.

Basic concepts and clinical findings in the treatment of seizure disorders with EEG operant conditioning

Two issues concerning sensorimotor EEG operant conditioning, or biofeedback, as a therapeutic modality for the treatment of seizure disorders are the focus of this review. The first relates to the question of whether relevant physiological changes are associated with this procedure. This question is addressed through review of an extensive neurophysiological literature that is likely unfamiliar to many clinicians but that documents both immediate and sustained functional changes that are consistent with elevation of seizure thresholds. The second focuses on the clinical efficacy of this method and whether it should carry the designation of "experimental". This designation is challenged through an assessment of over 25 years of peer-reviewed research demonstrating impressive EEG and clinical results achieved with the most difficult subset of seizure patients.

Trial-to-trial variability and state-dependent modulation of auditory-evoked responses in cortex

Recent experimental work has provided evidence that trial-to-trial variability of sensory-evoked responses in cortex can be explained as a linear superposition of random ongoing background activity and a stationary response. While studying single trial variability and state-dependent modulation of evoked responses in auditory cortex of ketamine/xylazine-anesthetized rats, we have observed an apparent violation of this model. Local field potential and unit spike trains were recorded and analyzed during different anesthesia depths-deep, medium, and light-which were defined by the pattern of ongoing cortical activity. Estimation of single trial evoked response was achieved by considering whole waveforms, rather than just one or two peak values from each wave. Principal components analysis was used to quantitatively classify waveforms on the basis of their time courses (i.e., shapes). We found that not only average response but also response variability is modulated by depth of anesthesia. Trial-to-trial variability is highest under medium levels of anesthesia, during which ongoing cortical activity exhibits rhythmic population bursting activity. By triggering the occurrence of stimuli from the spontaneously occurring burst events, we show that the observed variability can be accounted for by the background activity. In particular, the ongoing activity was found to modulate both amplitude and shape (including latency) of evoked local field potentials and evoked unit activity in a manner not predicted by linear superposition of background activity and a stereotyped evoked response. This breakdown of the linear model is likely attributable to rapid transitions between different levels of thalamocortical excitability (e.g., spike-wave discharges), although brain "state" is relatively fixed.

Physiological origins and functional correlates of EEG rhythmic activities: implications for self-regulation

Recent neurophysiological findings in relation to thalamocortical mechanisms for sensory processing, together with established anatomical and expanding functional evidence, have provided a rational theoretical framework for the interpretation of normal and abnormal EEG rhythmic activities. This perspective is integrated here with earlier animal studies which were the foundation for many current applications of EEG self-regulation as a clinical tool. Basic evidence concerning the origins, frequency modulation, and functional significance of normal EEG rhythmic activities is reviewed here in an effort to provide guiding principles for the interpretation of clinical abnormalities and their remediation with EEG feedback training.

Concepts and applications of EEG analysis in aviation performance evaluation

Quantitative studies of the human EEG during signal detection, flight simulation and actual flight performance tasks are reviewed here from the perspective of basic animal research on the neurophysiological and functional correlates of relevant rhythmic patterns. Evidence is examined which relates distinct EEG frequency changes to psychomotor behavior, signal processing and intrinsic attentional modulation during complex performance. Findings indicate that the EEG can provide a valid and objective index for mental effort but, in addition, may reveal task-related cognitive resource allocation, task mastery and task overload.

Temporal lobe and petit mal antiepileptics differentially affect ventral lateral thalamic and motor cortex excitability patterns

Evoked potential (EP) analysis of the somatomotor pathway in cats revealed that the temporal lobe anticonvulsant carbamazepine suppresses the thalamic relay, whereas the petit mal antiepileptic ethosuximide acts on the cortex. Moreover, a history of temporal lobe epilepsy (amygdala kindling) maximized thalamic response to carbamazepine, especially during sleep states vulnerable to generalized kindled seizures. Ethosuximide accentuated cortical response during sleep and awakening states vulnerable to generalized spike-wave complexes, regardless of a history of petit mal seizures (systemic penicillin epilepsy). The findings provide a neural basis for differential drug effects on generalized temporal lobe and petit mal epilepsy and further suggest that a chronic seizure disorder can create a predisposition for antiepileptic drug sensitivity.

EEG biofeedback and relaxation training in the control of epileptic seizures

Research utilizing sensorimotor rhythm (SMR) biofeedback with epileptics suggests that it is useful in decreasing seizures. Subjects were 6 young adults with a diagnosis of epilepsy of at least two years who had been unable to control their seizures with different regimens of anticonvulsant medications. Subjects ranged from severely mentally handicapped to above average functioning. Seizure type, frequency, and duration were recorded by subjects and caretakers. Measures of operant learning were percent time in SMR. The experiment utilized a single subject multiple baseline design which consisted of 6 phases: baseline one, relaxation training; baseline two, biofeedback training one; baseline three, biofeedback treatment two and follow-up. The results of this study are in agreement with other studies using SMR biofeedback. All subjects were able to significantly increase percent time in SMR. Five out of the 6 subjects demonstrated decreases in seizure frequency during the treatment phase. Two of the 6 subjects benefited from relaxation training. Four subjects demonstrated significant negative correlations between percent SMR and seizure rats. Consistent with other studies utilizing multiple baseline designs, a majority of the subjects did not follow the design of the study.

Sleep deprivation increases thalamocortical excitability in the somatomotor pathway, especially during seizure-prone sleep or awakening states in feline seizure models

Pathological somatomotor system excitability and generalized seizures occur throughout the sleep-awake cycle but peak at different times in the amygdala kindling and systemic penicillin epilepsy models. Sleep loss increases seizure activity in both models during all waking and sleep states but does not alter the timing of seizure susceptibility in the sleep-wake cycle. Although the mechanism for sleep-deprivation seizures is unknown, we propose that sleep loss magnifies somatomotor system hyperexcitability patterns in all states, thereby increasing seizure vulnerability at all times but preferentially during seizure-prone intervals. To evaluate this hypothesis, the timing of ventral lateral thalamic and motor cortex excitability, indexed by amplitudes of primary evoked responses, was studied throughout the sleep-wake cycle in eight cats before and after nearly total sleep deprivation. Sleep loss was induced by 24-h exposure to a modified "flower pot" procedure; the control procedure consisted of 24-h exposure to a larger pedestal which did not affect sleep time. Findings confirmed the hypothesis, as follows: (i) Sleep deprivation increased ventral lateral thalamic and motor cortical excitability nonspecifically. (ii) Motor cortex hyperexcitability correlated best with penicillin seizure activity; both were elevated in slow-wave sleep and drowsiness after awakening from slow-wave sleep before sleep loss and were further increased by sleep loss. (iii) Ventral lateral thalamic hyperexcitability patterns correlated best with the timing of kindled seizure susceptibility; both peaked during transitions from slow-wave to REM sleep before and after sleep loss but were maximal after sleep loss. (iv) Sleep loss increased thalamocortical excitability and seizure susceptibility during stable REM sleep in both models, but values were lower than in other states. These results suggest a chronic neuropathology at different levels of the neuraxis for dissimilar epilepsy models and upon which the sleep-waking state modulation of seizures is superimposed. Sleep deprivation may aggravate seizures in both models by nonspecific enhancement of thalamic and cortical excitability.

Thalamocortical mechanisms of state-dependent seizures during amygdala kindling and systemic penicillin epilepsy in cats

Somatomotor system-evoked potential data suggested that thalamus and cortex provide a final common pathway for the timing of generalized seizures in the sleep-wake cycle. Results indicated thalamic mediation of sleep-activated seizures in the amygdala kindling model of secondary generalized epilepsy; in contrast, cortical hyperexcitability was implicated in the timing of seizures with the systemic penicillin model of primary generalized, petit mal epilepsy. Even though thalamic or cortical hyperexcitability peaked during seizure prone sleep or awakening states in the two models, increased, 'subclinical' levels of hyperexcitability persisted during seizure resistant states, notably rapid-eye-movement (REM) sleep. This finding suggested a chronic, if often latent neuropathology for both epilepsy models and upon which the sleep-wake state modulation of seizures is superimposed.

Rapid eye movement (REM) sleep and ponto-geniculo-occipital (PGO) spike density are increased by somatic stimulation

It has been shown that REM sleep duration and ponto-geniculo-occipital (PGO) spike density can be enhanced by auditory stimulation. The purpose of this study was to determine whether this effect is restricted to the auditory sensory modality or whether somatic stimulation can produce similar effects. Cats implanted with electrodes for recording the sleep-wake cycle were additionally prepared with clip electrodes placed in the neck for somatic stimulation. Such stimulus was applied at the beginning and throughout each REM sleep period. The effect of this procedure was compared to a similar period when no stimulus was applied. The results showed that somatic stimulation induced a significant increase in REM duration (60.2%) and PGO spike density. Since the effects of somatic stimuli are identical to auditory ones, it is suggested that all sensory modalities may share the property of influencing the mechanisms which regulate the maintenance of REM sleep. Such mechanisms are discussed in terms of an increase in the excitability levels of polymodal medial reticular neurons.

A non-linear analysis of afferent modulatory activity in the cat somatosensory system

The effects of prior input on afferent activity in the somatosensory system of the cat have been studied using both twin-pulse experiments and random stimulus trains for which evoked activity is characterized by a set of mathematical functions known as kernels. The kernels quantitatively characterize transformational processes occurring in the system. The first-order kernel is analogous to a classical averaged evoked potential, but to temporally interacting stimuli; the second-order kernel may be likened to a generalized recovery function. Responses to superficial radial nerve stimulation were obtained at sensory (S1) cortex, thalamic n. ventralis posterolateralis (VPL), and the nucleus cuneatus of the dorsal column nuclei (DCN). Comparison of first-order kernels with averaged evoked potentials showed good agreement in chronic awake, chronic anesthetized, and acute anesthetized animals. Second-order kernels indicated complex interactions with an overall depression of subsequent response amplitudes. Comparison between second-order kernels and the results of the two-pulse experiments at both S1 cortex and VPL showed good agreement for early latency response components, but significant deviations for later components suggest higher than second-order non-linearities for this system.

Cortical visual evoked potentials during the sleep wakefulness cycle of the freely moving cat. Characterization and statistical comparisons

Visual evoked potentials (VEPs) were obtained during the stages of wakefulness (W), slow sleep (SS) and paradoxical sleep (PS) by means of a light-emitting diode chronically implanted in the frontal sinus of the freely moving cat. Statistical analysis of the variables: latencies, latency intervals and amplitudes, between each of the mentioned stages shows that, for the first components, variations occurred only in the first interval of latency during SS vs. W. Lengthening of VEP latencies and increase of VEP amplitudes were observed for all secondary components in the comparisons between both SS and W, and SS and PS. PS-VEPs vs. W-VEPs showed shortening of latencies and decrease of amplitudes of all secondary components of the former case. The results confirm that in the freely moving cat, the secondary VEP response is more intensely affected by sleep than the primary VEP response, but indicate that there are different mechanisms in the generation of the VEP during SS and PS.

Response of dopaminergic neurons in cat to auditory stimuli presented across the sleep-waking cycle

The response of dopaminergic neurons of the substantia nigra pars compacta to auditory clicks continuously presented across the sleep-wake cycle was studied in cats. The initial excitatory followed by inhibitory response to the click which occurred during quiet waking diminished as the cat progressed into slow-wave sleep and was absent during REM sleep. Upon awakening from REM sleep, dopamine neurons once again displayed an excitatory/inhibitory response to the clicks, implying that the decrease across the sleep-wake cycle was not attributable to long-term habituation.

The effects of deep barbiturate coma on multimodality evoked potentials

The authors report their investigation of the effects of high-dose barbiturates on the multimodality evoked response in 9 cats. After baseline evoked responses were obtained, boluses of pentobarbital were infused intravenously at regular intervals, amounting to cumulative total doses of 9, 18, 27, 45, 63, 123, and 183 mg/kg at respective infusions. This resulted in gradually increasing serum pentobarbital levels, reaching therapeutic coma levels (4 to 5 mg/dl) after the fifth infusion. At this point, the electroencephalogram was flat, and pressor agents were required to maintain cardiovascular stability. Evoked responses were obtained 15 minutes after each infusion. Brain-stem auditory evoked response (BAER) showed little change in wave latencies at therapeutic coma levels of pentobarbital. Further barbiturates resulted in delay of the late components of this response. In the somatosensory evoked responses (SER), early brain-stem components were relatively unaffected by therapeutic coma levels. Late brain-stem components and the initial cortical response showed progressive latency increase. Late cortical (association cortex) waves were abolished at relatively low doses. The central conduction time was relatively unaffected. The late waves of the visual evoked responses (VER) were abolished with low-dose barbiturates (9 mg/kg). A single positive-negative complex persisted despite massive infusions. It is concluded that evoked responses may prove useful in monitoring patients in deep barbiturate coma, but barbiturate effects must be kept in mind.

The effects of cold-induced brain edema and white-matter ischemia on the somatosensory evoked response

The electrophysiological effects of cold-lesion edema and white-matter ischemia were studied in cats by reference to the short-latency somatosensory evoked response. The primary cortical waves were found to be considerably delayed following a period of white-matter ischemia; hosever, cold-lesion edema appeared to have no significant effect on the evoked response. The authors conclude that vasogenic edema does not interfere with axonal functioning by an ischemic mechanism.

The reactivity of the somesthetic S1 cortex during sleep and waking in the rat

The reactivity of the somesthetic S1 cortex was studied in the rat, in the course of the seven principle stages of the sleep-waking cycle, in terms of the variation in amplitude of positive wave 4 of the evoked potential induced by stimulation of the thalamocortical radiations. The amplitude of positive wave 4 is minimal during waking with theta (attentive and/or active). It increases in the course of waking without theta, to reach its maximum during the stage of sleep with slow waves. The amplitude decreases with the deepening of slow sleep (spindles, intermediate stage) to a level near to waking without theta, during rapid sleep. No significant difference is observed during periods of eye movements bursts. The variability of the amplitude of intra-state responses is lowest in the phases of waking and paradoxical sleep. The recovery cycle of the S1 cortex responses is long (several hundreds of milliseconds). The rate of recovery is inversely proportional to the amplitude of the response to the conditioning stimulus. It is therefore higher during waking and rapid sleep than during the different stages of slow sleep. These results are integrated in the neurophysiological data of sleep in the rat.

Changes in seizure susceptibility, sleep time and sleep spindles following thalamic and cerebellar lesions

The present experiment attempted to clarify conflicting evidence on the relationship of sleep spindles to seizure activation. Seizure thresholds were calculated in minutes post-injection following IP administration of the convulsant drug monomethylhydrazine (MMH) to cats with lesions intended to alter the occurrence of spontaneous 12-15 c/sec sleep spindles recorded from sensorimotor cortex. Twelve cats with bilateral cortical and subcortical recording electrodes were divided into 3 groups receiving electrolytic lesions in the dentate nucleus (group I), the ventrobasal (VB) thalamus (group II), or in one of various 'control' regions (group III). Lesion sites in group III animals avoided primary afferent pathways to VB thalamus, destruction of which has been found to enhance sleep spindle activity, and included cerebellar white matter and ventral pontine tegmentum. Prior to the MMH trials, baseline EEGs were obtained during pre- and post-lesion conditions. Following the MMH trial, lesions were verified histologically. Results of the MMH trial revealed that animals with dentate and ventrobasal thalamic lesions showed elevated seizure thresholds and slow wave sleep times relative to their own pre-lesion EEG baselines and to the pre- and post-lesion baselines of control animals. Furthermore, an increased incidence of sleep spindles was associated with dentate lesions while animals with ventrobasal thalamic lesions showed a shift in frequency from 8-11 c/sec to 12-15 c/sec activity during that state. These findings are compatible with the view that sleep spindles do not facilitate seizure activation and may, in fact, exert a protective influence.

Somesthetic cortex reactivity during sleeping and waking in the rat

The cortical S1 responsiveness was studied by unique and coupled stimuli of non-maximal intensity applied to somesthetic radiations. The reactivity is highest during sleep with slow waves, lowest during active waking, intermediate during non-active waking and rapid sleep. The recovery of responsiveness presents an exactly opposite form and begins at a long interstimulus delay (greater than 150 msec).

Study of cortical spindles during sleep in the rat

A systematic analysis of the dorsally accessible cortical areas has been undertaken so as to study the space-time distribution, the intrinsic characteristics and the physiological appearance modalities of cortical spindles in the rat. After falling asleep, the animal presents anterior spindles of which the number, duration and amplitude increase as sleep with slow waves deepens. These spindles are fully developed during intermediate state which precedes and follows paradoxical sleep, where they are associated with a theta rhythm in the hippocampus and the visual cortex. These spindles, at their maximum in anterior regions, lose intensity as one approaches the cerebellum. Uniquely during slow wave phase of sleep, the rat presents posterior spindles which are predominant in the occipital region, are less marked in parietal and cerebellar regions and disappear in the frontal cortex. Less frequent than anterior spindles, they are significantly distinguished by their lower amplitude, higher frequency and shorter duration.

Evoked K-complexes and cardiovascular responses to spindle-synchronous and spindle-asynchronous stimulus clicks during NREM sleep

The hypothesis that the functional role of the sleep spindle is to preserve sleep by inhibiting sensory input (Yamadori 1971) was examined. Series of 44 dB, 10 msec, 1000 c/sec 'clicks' were presented to 12 subjects at a 30-sec ISI during stage 2 sleep either during spindle bursts (i.e. spindle-synchronous clicks) or during interburst periods (i.e. spindle-asynchronous clicks). Contrary to the spindle inhibitory hypothesis, cortical EEG and cardiovascular responses showed no evidence of spindle 'suppression'. Evoked K-complexes were potentiated by the spindle-synchronous stimulation. A second study with 7 subjects replicated this result and extended the finding to include stage 3--4 sleep. It was suggested that the potentiation of evoked K-complexes was due to phasic reductions in inhibitory action during sleep spindles resulting in increased transmission of sensory events or, perhaps, an increase in the lability of certain EEG response systems.

Depression of evoked potentials in rat thalamic ventro-basal complex and somatosensory cortex after reticular stimulation

Experiments on unanesthetized rats immobilized with D-tubocurarine showed that electrical stimulation (100/sec) of the central gray matter and the mesencephalic and medullary reticular formation considerably depressed potentials in the somatic thalamic relay nucleus and somatosensory cortex evoked by stimulation of the forelimb or medial lemniscus. The mean threshold values of the current used for electrical stimulation of these structures did not differ significantly and were 70 (20--100), 100(20--120), and 120 (50--200) muA, respectively. On comparison of the amplitude-temporal characteristics of inhibition of evoked potentials during electrical stimulation of the above-mentioned structures by a current of twice the threshold strength, no significant differences were found. Immediately after the end of electrical stimulation the amplitude of the cortical evolved potential and the post-synpatic components of the thalamic evoked potential was 50--60% (P less than 0.01) below the control values. The duration of this depression varied from 0.5 to 1 sec. An increase in the intensity of electrical stimulation of brain-stem structures to between three and five times the threshold led to depression of the presynaptic component of the thalamic evoked potential also. Depression of the evoked potential as described above was found with various ratios between the intensities of conditioning and testing stimuli.

The definition of waking stages on the basis of continuous polygraphic recordings in normal subjects

Polygraphic examinations were made during the day on 6 normal subjects. Simultaneous evaluation of EEG, EOG and EMG was carried out over 30 sec epochs. The data thus obtained were correlated with the various types of behaviour and activities during the day and then interpreted. Six conditions could be defined corresponding to different waking stages. The analysis of the material obtained shows that the existence of these waking stages is of interindividual validity.

The effects of feedback on focal epileptic discharges in man. A preliminary report

The history of the control of epileptic disturbances by conditioning techniques is reviewed. The preliminary results of a three year trial of feedback techniques in 13 epileptic patients are presented. Thirteen epileptic patients (age 2.5 leads to 39 mean, 15.1 years) with lateralized focal discharges in the EEG were given repeated trials of feedback, the focal discharges being used to trigger auditory and somatosensory stimuli. Dosages and serum levels of medication were unchanged throughout the experimental period. The number of epileptic spikes per 15 seconds was assessed by automatic trend analysis during 20 to 30 minute control, biofeedback and post-feedback epochs. On-going EEG activity was quantified by 8 channel frequency analysis over 10 second epochs. The patients made efforts to increase and decrease the number of spike discharges with and without feedback and the results of both triggered and random auditory, somatosensory, photic and combined stimulation were compared at various intervals over a period of up to three years. A marked reduction in the number of focal discharges was noted in eight (61.5%) patients during and immediately following the sessions. Intermittent biofeedback sessions were not associated with a serial reduction in the number of focal EEG discharges. There was a reduction in the number of clinical epileptic disturbances in six patients (46%) and possible reasons for this improvement are discussed. One patient suffered an increase in focal temporal lobe discharges during triggered and random auditory stimulation whereas there was a marked reduction in the number of discharges during minimal electrical stimulation of the contralateral arm. The need for careful assessment of each patient to determine appropriate feedback stimulation is stressed. One aim of this research has been to assess the feasibility of using miniature units for continuous feedback of focal discharges in epileptic patients.