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

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.