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

Mice Lacking Cerebellar Cortex and Related Structures Show a Decrease in Slow-Wave Activity With Normal Non-REM Sleep Amount and Sleep Homeostasis

In addition to the well-known motor control, the cerebellum has recently been implicated in memory, cognition, addiction, and social behavior. Given that the cerebellum contains more neurons than the cerebral cortex and has tight connections to the thalamus and brainstem nuclei, it is possible that the cerebellum also regulates sleep/wakefulness. However, the role of the cerebellum in sleep was unclear, since cerebellar lesion studies inevitably involved massive inflammation in the adjacent brainstem, and sleep changes in lesion studies were not consistent with each other. Here, we examine the role of the cerebellum in sleep and wakefulness using mesencephalon- and rhombomere 1-specific Ptf1a conditional knockout (Ptf1a cKO) mice, which lack the cerebellar cortex and its related structures, and exhibit ataxic gait. Ptf1a cKO mice had similar wake and non-rapid eye movement sleep (NREMS) time as control mice and showed reduced slow wave activity during wakefulness, NREMS and REMS. Ptf1a cKO mice showed a decrease in REMS time during the light phase and had increased NREMS delta power in response to 6 h of sleep deprivation, as did control mice. Ptf1a cKO mice also had similar numbers of sleep spindles and fear memories as control mice. Thus, the cerebellum does not appear to play a major role in sleep-wake control, but may be involved in the generation of slow waves.

Transitory sleep spindles impairment in deep cerebral venous thrombosis

Sleep spindles may be affected by thalamic or hemispheric ischemic stroke. However, spindles reduction and their relationship with K-complexes following deep cerebral venous thrombosis have not been reported. An 18-year-old woman suffered from a deep cerebral venous thrombosis with vasogenic oedema located predominantly in the thalami. Stage 2 sleep EEG recorded in acute setting showed preservation of K-complexes but absent 12-14 Hz sleep spindles, which were replaced by spindle-like theta oscillations. One month later, the patient having completely recovered, sleep spindles were normally seen on the control EEG. This case illustrates that deep cerebral venous thrombosis, through a vasogenic oedema, may transiently affect thalamic functions such as spindles generation. Furthermore, thalamic impairment may lead to dissociation of spindle and K-complex activity.

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.

Anticonvulsant drugs selectively affect kindled and penicillin epilepsy, especially during seizure-prone sleep or awakening states in cats

Carbamazepine (CBZ) selectively suppressed kindled convulsions, whereas ethosuximide (ESM) suppressed spike-wave activity accompanying systemic penicillin epilepsy in cats. Evoked potential data indicated that CBZ acted at the thalamic level, whereas ESM acted at cortex. Reduction of seizures and thalamic or cortical excitability occurred throughout the sleep-wake cycle, but effects were most pronounced in seizure-prone sleep or awakening states. These findings extend previous work showing differential antiepileptic drug (AED) effects on temporal lobe and absence seizures. The results are also consistent with recent work suggesting that thalamocortical pathways provide a final common pathway for the manifestation of sleep and awakening epilepsy and also reflect a chronic, latent pathophysiology.

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.

Multiunitary activity analysis of cortical and subcortical structures in paroxysmal discharges and grand mal seizures in photosensitive baboons

Cortical and subcortical multiunitary activities (MUA) and EEG were simultaneously recorded in baboons made photosensitive by a subconvulsant dose of DL-allylglycine. Intermittent light stimulation (ILS) trains induced in these animals fronto-rolandic (FR) paroxysmal discharges (PDs, constituted as spikes and waves) and grand mal seizures. During the induction of FR PDs by ILS trains, the visual structures (occipital cortex, colliculi superioris, pulvinar) showed a significant MUA increase which was not related to the PD spike or wave but correlated with the flashes. The first structure showing bursts of MUA that frequently preceded the PD appearance was the FR cortex. When PDs appeared, the bursts were related to the spikes of PDs and were followed by an inhibition during the slow wave. The pontine and mesencephalic reticular formations and the facial nuclei were activated in bursts after the FR PDs had reached a certain amplitude. The thalamic nuclei ventralis lateralis, centrum medianum and lateralis posterior were activated only later, when the FR PDs had reached an even greater amplitude. It is suggested that the activation of visual structures is necessary for FR PD appearance. The secondary pontine and mesencephalic activation could reinforce that of the FR cortex and then the thalamus, and could determine the myoclonus observed in unparalysed animals. When the ILS is continued, grand mal seizures appear. The onset of the seizures could be linked to the loss of FR cortical control of the subcortical structures. The resulting reticular activation would be responsible for the vasomotor modifications which constitute the first clinical signs of a seizure.

'Kindling' a sleep disorder: degree of sleep pathology predicts kindled seizure susceptibility in cats

Progressive sleep deficits accompanying the gradual development of a kindled seizure disorder in cats persist at least one month after kindling and correlate with subsequent seizure thresholds. These parallels between the two pathologies suggest the kindling of a sleep disorder which occurs in addition to, and may be a determinant of, the kindled seizure disorder.

Participation of the cerebellum in the regulation of the sleep-wakefulness cycle. Results in cerebellectomized cats

To study the participation of the cerebellum in the sleep-wakefulness cycle, 6 totally cerebellectomized cats and 3 craniectomized sham-operated controls were used. Cerebellectomies were performed by aspiration or by bilateral sections of the cerebellar peduncles. Chronic modifications in the total amount, duration and frequency of episodes of wakefulness (W), drowsiness (D), slow sleep (SS) and paradoxical sleep (PS) were examined. In each group of animals, statistical comparisons between the pre- and postlesion values were made. No changes in the total amount of W, D, SS and PS were observed in the sham-operated group. In all postlesion experiments, cerebellectomized cats presented a statistically significant increase of D (major number of episodes). W, SS and PS modifications only reached statistical significance when considering the whole survival period of the cerebellectomized animals. These consisted in decrease of W and SS (shortening of episodes) and increase of PS (lengthening of episodes). The results, which are discussed in the light of a dual opposing influence of cerebellar cortex and deep cerebellar nuclei on the SWC, indicate an important participation of the cerebellum in the mechanisms of the synchronized EEG together with a regulatory action on fine adjustments of the proportions of the SWC states.

Power spectral analysis of EEG characteristics during sleep in epileptics

Power spectral analysis of spontaneous EEG activity recorded during non-rapid eye movement (REM) sleep was employed in an effort to identify characteristic EEG substrate abnormalities in epileptics. All-night polygraphic recordings were obtained from 10 poorly controlled subjects with mixed and generalized seizures. Similar data were obtained from 10 matched nonepileptic subjects. Continuous 10 min samples of non-REM sleep were identified at the beginning and end of these all-night recordings. EEG activity recorded during these periods from left sensorimotor and parieto-occipital bipolar leads was digitized, subjected to the fast Fourier transform, and then sorted into successive 4 Hz frequency bands between 0 and 23 Hz. Mean spectral density was determined for each frequency band from both samples in both groups. Comparison of these values disclosed both similarities and differences between the two groups. All subjects showed a significant "time-of-night effect," with power at 0-3, 4-7, and 8-11 Hz greater at the beginning of the night. This finding was related to a similar observation in developing infants and attributed to a circadian influence on neuronal generators. In group comparisons, epileptics showed selective differences in common when compared with nonepileptics. These differences were reduced when data from a small group of unmedicated epileptic subjects were partialled out. Medicated epileptics showed differences restricted to the early morning non-REM sleep sample, which included significantly greater power at 4-7 Hz and significantly lower power at 12-15 Hz. Unmedicated subjects showed these differences in both samples and also showed significantly greater power in the 0-3 Hz band. It was suggested that anticonvulsant medications may exert a general normalizing influence on EEG characteristics during sleep, particularly at the beginning of the night in proximity to their administration. The documentation of significant EEG deviations restricted to two basic rhythmic patterns during sleep suggests a disturbance of underlying thalamocortical mechanisms.

Quantitative analysis of training, sleep EEG and clinical response to EEG operant conditioning in epileptics

This report is a follow-up to a previous paper which described seizure rate changes with central cortical EEG feedback training in 8 poorly controlled epileptic subjects. Data examined here include associated training compliance and performance, sleep EEG spectra, clinical EEG and anticonvulsant blood levels. The study employed a double-cross-over, single blind ABA design applied to two subgroups of epileptic patients. Both groups had in common two training periods (A1, A2) in which either 12--15 c/sec (subgroup I, n = 4) or 18--23 c/sec (subgroup II, n = 4) was reinforced in the absence of 6--9 c/sec, movement or epileptiform discharge, and one training period (B) in which 6--9 c/sec was reinforced in the absence of 12--15 or 18--23 c/sec as well as movement and epileptiform discharge. Training periods occurred primarily in the home and lasted 3 months. Compliance with training instructions and response acquisition were demonstrated. Overall anticonvulsant blood levels were low and unrelated to EEG or seizure changes. Clinical EEG findings corresponded to sleep EEG and seizure rate outcomes. Power spectral analysis of sampled non-REM sleep from all-night EEG recordings obtained after each training phase indicated contingency specific changes which were limited to sensorimotor recordings in subgroup I and corresponded to the pattern of seizure rate changes in this group. EEG changes were also limited to sensorimotor cortex in subgroup II, but were linear and paralleled a progressive decrease in seizure rate. Both groups, however, showed the same pattern of EEG changes with seizure reductions; low and high frequencies were reduced and intermediate, rhythmic frequencies increased. Correlational analysis confirmed this relationship. The pattern, duration and topographic specificity of these changes suggested a normalization of sensorimotor EEG substrates related to the EEG feedback traning.