Electrocortical arousal and spindles on physiological cortico-subcortical interactions

The neuronal mechanisms of electrocortical arousal and sleep spindles were reviewed on the basis of intracellular analyses on the motor cortex in atraumatically maintained encéphale isolé cat preparations. When arousal is initiated by subcortical afferents from the brainstem, the cortical neurons respond with either excitation (E), inhibition (I), disfacilitation (DF), or disinhibition (DI), in a cascade pattern proceeding from the superficial to deep layers. These neuronal activities on arousal involve DF of the output neurons that may set the subcortical sensorimotor functions in a readiness state for a possible adaptive behavior of animals. This initial transient arousal termed phasic develops soon to the next, more sustained phase termed tonic by the action of other subcortical afferents. The cascade transmissions then occur again, producing E, I, DF, and DI in the cortical neurons but with a reverse laminar pattern proceeding from the deep to superficial layers. These neuronal activities on tonic and arousal deliver the cortical outputs to the subcortical systems that may trigger an orienting or searching behavior of animals in their environment. Sleep spindles also accompany the cascade transmissions that are partly common to those in arousal. Various modes of the cascade transmissions were further examined by applying electric shock stimuli to the cortical surface, the ventrolateral nucleus of the thalamus, and the cerebral peduncle to activate the subcortical afferents converging onto different cortical layers. The combined results from these experiments may imply that the cortico-subcortical interactions in which all the cortical neurons participate with dynamic harmony are instrumental to set a physiological sequence of animal behavior. If these interactions be impaired on the way of normal growth of the brain, as in the case of disorders with the Rett syndrome, many forms of ill adaptation may be brought about by dedifferentiation of sensorimotor functions.