Ensemble reactions of neurons in the reticular formation of the cat--categorization of inputs and temporal influences.

A method of recording ensemble reactions of reticular neurons was applied in anesthetized cats to obtain information about categorization of inputs and the influence of the time factor upon a pattern of responses, reactions to stimulus intensity changes and to complex stimuli, and temporal influences with their relation to plastic changes induced by iterative stimulation. In spite of some variability of the pattern of responses evoked in the reticular formation (RF) by electrical stimulation of the same source, reactions of the parenchyma of the RF differentiate heterotopic stimuli; reactions evoked from receptor areas situated closely to each other exhibited a similar pattern whereas less resemblance was found in the case of responses evoked from sources with a heterosegmental projection and from contralateral sources. Stimulus intensity changes did not influence substantially the pattern of recordings in the RF. The noticeable effect resulting from the increase of stimulus intensity was enlargement of responses. A complex stimulus (two heterotopic stimuli applied simultaneously) was manifested by a reaction which, in comparison with reactions evoked from each of both sources separately, had a different pattern. A trend of changes in the size of responses evoked in the RF by continuous stimulation (60 stimuli, 0.3 Hz) was observed only in some cases. Abrupt alterations of the stimulation rate (0.3 Hz in equilibrium 1 Hz, 0.3 Hz in equilibrium 2 Hz) resulted in a prompt change in responses. With constant stimulation conditions, this activity was fairly constant with an absence of trends. Persistent changes were observed only in a minority of cases. The neuronal apparatus of the RF computes ongoing effects on the basis of ability to discriminate different inputs and to readily change its function. The extent to which the RF holds information about the antecedent "history" of its functioning and the extent to which intrinsic mechanisms of the RF by itself are responsible for behavioral habituation remains problematical.