Dentate granule cell discharge during conditioning. Relation to movement and theta rhythm

The activity of dentate granule cells (g-cells) was recorded in chronic rats during single-tone sensory discrimination performance. Attempts to correlate the discharge pattern of dentate g-cells with (1) the onset of the conditioned tone stimulus, (2) movements of the animals during the conditioning trials, (3) the occurrence of the reinforced response, and (4) the presence or absence of theta rhythm during the trial revealed several features of g-cell discharge during performance of operant sensory discrimination. The most consistent finding was that g-cells were driven at short latencies (40-60 ms) by the onset of the tone stimulus in the absence of detectable body movements. A subsequent, less intense sustained discharge of g-cells was shown to be unrelated to the onset of (1) conditioned movements during the trial, or (2) the execution of the conditioned response. Thus neither phase of g-cell discharge to the tone stimulus appeared to be a direct correlate of inadvertently or directly conditioned movements in this experimental paradigm. Theta rhythm, which accompanied certain movements prior to the execution of the operant response, did not correlate with the initial phase of g-cell discharge but appeared to modulate the subsequent phase of sustained g-cell activity.