The pharmacology of hippocampal theta cells: evidence that the sensory processing correlate is cholinergic.

The firing repertoires of theta cells in the CA1 and dentate layers of the hippocampal formation of the freely moving rabbit were analyzed during 3 behavioral conditions: (1) voluntary motor patterns, termed type 1 theta behaviors; (2) automatic motor patterns, termed type 2LIA behaviors; (3) alert immobility with presentation of sensory stimuli, termed type 2 theta behavior. Cholinergic manipulations were shown to effect the firing repertoires of theta cells during the type 2 theta behavior condition (sensory processing) and not the other two behavioral conditions. A hypothesis of a sensorimotor processing function of the hippocampal formation is presented and discussed.

The relation of multiple hippocampal theta cell discharge rates to slow wave theta frequency.

Multiple theta cells in the dentate granule cell area of the hippocampal formation of the freely moving rabbit were analyzed during three behavioral conditions: (1) voluntary motor patterns, termed Type 1 theta behaviors; (2) automatic motor patterns, termed Type 2 LIA behaviors; (3) alert immobility with presentation of sensory stimuli, termed Type 2 theta behavior. Multiple theta cells showed a linear increase in discharge rates, with increasing frequency of slow wave theta, in both the Type 1 and Type 2 theta conditions. Although there was no mean overlap in discharged rates (from one frequency to the next highest frequency of slow wave theta), individual data points overlapped considerably in the middle ranges. Multiple theta cell discharge rates were significantly lower in the Type 2 theta condition compared to the Type 1 theta condition, even at identical slow wave theta frequencies. Multiple theta cells discharged in an irregular fashion during the Type 2 LIA behavior condition. The discharge pattern was characterized as on or off, the on pattern most commonly observed being asynchronous bursting.