SYNCHRONOUS MODULATION OF PERIRHINAL CORTEX NEURONAL-ACTIVITY DURING CHOLINERGICALLY MEDIATED (TYPE-II) HIPPOCAMPAL THETA

The perirhinal cortex (PRC) plays a major role in memory processes. Th is role may be influenced by activity in the adjacent entorhinal corte x (EC) and hippocampus (HPC), particularly during the processing of sp atial information. In the current experiment we sought to determine wh ether the cholinergically mediated (type II) theta rhythm, which is a prominent electrophysiological feature of both HPC and EC activity, in fluenced neuronal firing in the PRC of urethane-anesthetized rats. Whe n the spontaneous firing activity of single units recorded in PRC was related to theta recorded from the hippocampal fissure, it was determi ned that the firing of 50/163 (31%) PRC neurons exhibited a statistica lly significant phase relationship (mean phase angle = 188 degrees) to HPC theta. Thirty-three (66%) of these neurons tended to fire near th e trough, and 17 near the peak, of this activity. These data indicate that a high proportion of PRC neurons participate in hippocampal-entor hinal theta activity. This activity may support information transmissi on and storage within and between these structures. (C) 1998 Wiley-Lis s, Inc.