Hippocampal unit activity to tonal stimuli during arousal from sleep and in awake rats

Abstract

Single cell activity was recorded from electrodes chronically implanted in fascia dentata and the CA-1 field of dorsal hippocampus in unrestrained rats during presentations of tonal stimuli. In the first experiment 32% of the cells showed reliable decreases in activity to the tonal stimuli and 26% showed reliable increases. Most of these cells (73%) habituated under rapid tone presentation. The second experiment showed that tonal stimuli caused changes in activity in more cells when the tones aroused the animal from sleep (75% affected) than when the tone was presented to an awake animal (18% affected). In both experiments all affected fascia dentata cells were inhibited. However, 36% of the affected CA-1 cells were augmented. The data indicate that the hippocampus undergoes dramatic changes during arousal from sleep, and that previously found changes in hippocampal activity during conditioning might be due to conditioned changes in the capability of stimuli to arouse the animal from sleep.