[Intracellular studies on the influence of inhibiting potentials in the motor cortex. II. The effect of electric stimulation of the nucleus caudatus]

The caudate: a key node in the neuronal network imbalance of insomnia?

Insomnia is prevalent, severe and partially heritable. Unfortunately, its neuronal correlates remain enigmatic, hampering the development of mechanistic models and rational treatments. Consistently reported impairments concern fragmented sleep, hyper-arousal and executive dysfunction. Because fronto-striatal networks could well play a role in sleep, arousal regulation and executive functioning, the present series of studies used an executive task to evaluate fronto-striatal functioning in disturbed sleep. Patients with insomnia showed reduced recruitment of the head of the left caudate nucleus during executive functioning, which was not secondary to altered performance or baseline perfusion. Individual differences in caudate recruitment were associated with hyper-arousal severity. Seed-based functional connectivity analysis suggested that attenuated input from a projecting orbitofrontal area with reduced grey matter density contributes to altered caudate recruitment in patients with insomnia. Attenuated caudate recruitment persisted after successful treatment of insomnia, warranting evaluation as a potential vulnerability trait. A similar selective reduction in caudate recruitment could be elicited in participants without sleep complaints by slow-wave sleep fragmentation, providing a model to facilitate investigation of the causes and consequences of insomnia.

Electrophysiological effects and clinical results of direct brain stimulation for intractable epilepsy

OBJECTIVE

Epilepsy can be considered as a result of the imbalance of the excitatory and inhibitory processes. Therefore, the artificial enhancement of the activity of brain inhibitory mechanisms might lead to a beneficial therapeutic effect for intractable epilepsy patients.

MATERIAL AND METHODS

Studies of the inhibitory effects of electrical stimulation of the head of the caudate nucleus (HCN), cerebellar dentate nucleus (CDN), thalamic centromedian nucleus (CM), and neocortical and temporal lobe mesiobasal epileptic foci were performed on 150 patients with implanted intracerebral electrodes. Chronic brain stimulation with implanted neurostimulators was performed on 54 patients. Sixteen were followed up to 1.5 years (mean 1.2 years).

RESULTS

The study demonstrated that 4-8 Hz HCN and 50-100 Hz CDN stimulation suppressed the subclinical epileptic discharges and reduced the frequency of generalized, complex partial, and secondary generalized seizures. CM stimulation (20-130 Hz) desynchronized the EEG and suppressed partial motor seizures. Direct subthreshold 1-3 Hz stimulation of the epileptic focus may suppress rhythmic afterdischarges (ADs). Seizures were eliminated for 26 of 54 patients (48%), worthwhile improvement was achieved for 23 of 54 patients (43%), and no improvement was observed in 5 of 54 patients (9%).

CONCLUSION

The artificial increase of the activity of brain inhibitory system may suppress the activity of epileptic foci, and, in long run, stabilize this epileptic foci activity at a lower, perhaps normal, level. Therapeutic direct brain stimulation, therefore, might serve as a useful tool in the treatment of intractable and multifocal epilepsy, and might be combined with ablative surgical methods.

Cross-Correlation Analysis of Electroencephalographic Potentials and Slow Membrane Transients

Cross-correlation analysis reveals a close correlation between the waves in an electroencephalogram and slow membrane transients of single neurons of the sensorimotor cortex of cats during spontaneous activity, augmenting and recruiting responses, and after local application of strychnine. Time-series correlation coefficients up to 0.7 have been computed. It is suggested that the waves of the electroencephalogram reflect an integration of the changes of membrane potentials in both the cell bodies and dendrites of cortical neurons.

POSTSYNAPTIC POTENTIALS AND SPIKE PATTERNS DURING AUGMENTING RESPONSES IN CAT'S MOTOR CORTEX

Intracellular recordings and electroencephalograms were obtained from neurons of the motor cortex during augmnenting responses elicited by repetitive stimulation of its specific thalamic nucleus. The postsynaptic potentials during fully developed augmenting responses consistedf two depolarizing waves with two separate groups of spike dicharges of different latencies, the bases of the spikes, the so-called "firing-levels," sometimes shifting. This supports the concept that the postsynaptic potentials accompanying the augmentintg response consist of a primary response and a response of recruiting character.