Summary
Two main types of neurons were recorded in the dorsal hippocampus of chronic rats. Type I neurons were characterized by a bursting mode of discharge. Their activity was higher during slow wave sleep (SWS) than during wakefulness (W) or paradoxical sleep (PS). They had an “inhibitory” response (decrease in spike frequency) to desynchronizing stimuli presented during a SWS episode. Type II neurons had a mean spike frequency greater than 10/s. Some of them, (group IIa), were more active during W and PS than during SWS and had an “excitatory” response (increase in spike frequency) to desynchronizing stimuli. Activity of other type II neurons, group IIb, had no relationship with the arousal level.
An arousal response (neocortical EEG desynchrony) was classically conditioned to an acoustical CS. During that conditioning, most of the type I neurons rapidly displayed an inhibitory conditioned response (CR). This unit response was closely associated with the EEG CR. The majority of the type II neurons did not demonstrate signs of conditioning (group IIb). The others, group IIa, gradually developed an excitatory CR at moderate levels. This unit CR seemed to be independent of conditioned modifications of arousal.
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Delacour, J. Conditioned modifications of arousal and unit activity in the rat hippocampus. Exp Brain Res 38, 95–101 (1980). https://doi.org/10.1007/BF00237935
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DOI: https://doi.org/10.1007/BF00237935