Hippocampal plasticity during jaw movement conditioning in the rabbit.

Hippocampal CA1 unit responses were recorded during classical conditioning of rhythmic jaw movements in New Zealand White rabbits. Training was accomplished using a 1 kHz tone as the conditioned stimulus (CS) and 1 ml of sweetened water as the unconditioned stimulus (US). The interstimulus interval was 250 ms. Daily sessions consisted of 48 paired trials and six tone alone test trials, with an intertrial interval averaging 60 s. Controls were given explicitly unpaired stimuli. Unit and behavioral conditioned responses developed very rapidly in the trained group, but did not occur in controls. Averaged unit poststimulus histograms showed a correspondence between rhythmic cell discharges and the periodicity of the behavioral conditioned response after training. The results are discussed in relation to a hippocampal role in the modulation of learned movement patterns.