"Training" of subicular neurons and the theta rhythm.

The impulse activity of subicular neurons during electrical stimulation of the dorsal hippocampus with repeated, single impulses or groups of impulses with variable interimpulse intervals was studied in acute experiments with nembutalized, immobilized cats. Sibicular neurons can be divided into two groups according to the character of responses: One group responds with phasic excitation reactions in accordance with the rhythm of excitation; the other, with inhibition. The second group of neurons in the course of stimulation reorganizes its activity and begins generating impulses that anticipate rhythmic stimulations. The extrapolating action of these neurons is observed only at interstimulus intervals corresponding to the theta rhythm. The significance of the hippocampal rhythm in memory phenomena is discussed.