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M Steriade

Publications and source records attributed to M Steriade.

221 records · Page 13Linked to original sources
PubMedDate not supplied

[Methodological aspects of a renewed study of ascending activation of mesencephalic reticular origin (author's transl)].

The phenomena of activation of the thalamocortical systems at the cellular level consist of an increase in the level of spontaneous discharges from thalamo- and corticifugal neurones, an increase in their reactivity to antidromic volleys, and inhibitory processes with rapid development. All these events occur on a base of EEG desynchronization, can be provoked by electrical stimulation of the reticular formation, but are also observed during active behaviocal states: waking periods and desynchronized sleep. After a brief analysis of the contradictions arising from studies on the ascending reticular system using the conventional methods of stimulation-lesion, the results of micro-injections of kainic acid into the mesencephalic reticular formation, compound which excites and then destroys intrinsic neurones without affecting passing fibres, are presented. The qualities necessary for conducting a study at the unitary level are the physiological identification of reticular neurones with rostral projection, and the analysis of their activity to test two hypotheses: that these neurones maintain the tonic phenomena of thalamocortical activation, and that precursor alterations in their activity could be the basis for transitions between synchronized sleep and the waking state. The data resulting from the unitary analysis of the mesencephalic reticular neurones physiologically identified in the behaving animal will be presented to support these hypotheses.

Cerebral Cortex↗
PubMedDate not supplied

Impact of intrinsic properties and synaptic factors on the activity of neocortical networks in vivo.

To investigate the relative impact of intrinsic and synaptic factors in the maintenance of the membrane potential of cat neocortical neurons in various states of the network, we performed intracellular recordings in vivo. Experiments were done in the intact cortex and in isolated neocortical slabs of anesthetized animals, and in naturally sleeping and awake cats. There are at least four different electrophysiological cell classes in the neocortex. The responses of different neuronal classes to direct depolarization result in significantly different responses in postsynaptic cells. The activity patterns observed in the intact cortex of anesthetized cats depended mostly on the type of anesthesia. The intracellular activity in small neocortical slabs was composed of silent periods, lasting for tens of seconds, during which only small depolarizing potentials (SDPs, presumed miniature synaptic potentials) were present, and relatively short-lasting (a few hundred milliseconds) active periods. Our data suggest that minis might be amplified by intrinsically-bursting neurons and that the persistent Na+ current brings neurons to firing threshold, thus triggering active periods. The active periods in neurons were composed of the summation of synaptic events and intrinsic depolarizing currents. In chronically-implanted cats, slow-wave sleep was characterized by active (depolarizing) and silent (hyperpolarizing) periods. The silent periods were absent in awake cats. We propose that both intrinsic and synaptic factors are responsible for the transition from silent to active states found in naturally sleeping cats and that synaptic depression might be responsible for the termination of active states during sleep. In view of the unexpected high firing rates of neocortical neurons during the depolarizing epochs in slow-wave sleep, we suggest that cortical neurons are implicated in short-term plasticity processes during this state, in which the brain is disconnected from the outside world, and that memory traces acquired during wakefulness may be consolidated during sleep.

Anesthesia, General↗
PubMedDate not supplied

Sleep oscillations in corticothalamic neuronal networks and their development into self-sustained paroxysmal activity.

Electrophysiological studies in cats have shown that one of the most common forms of sleep oscillation, spindling, may develop into spike-and-wave discharges through repetitive spike-bursts transmitted along thalamocortical or corticothalamic axons. The lowered frequency (from around 10 Hz to 3 Hz) can be explained by the abnormally increased duration of an IPSP mediated by GABA receptors. The administration of ethosuximide has a twofold effect resulting in a diminished spindling activity of the reticular thalamic nucleus as well as a decrease in the incidence of epileptic spike-and-wave discharges. Self-sustained paroxysmal activity may develop during EEG synchronized states by repetitively setting into action reciprocally connected structures.

Action Potentials↗