Macroelectrode responses with stimulation and recording within hippocampus and related structures during different states of consciousness.

Three or four pairs of bipolar electrodes were chronically implanted in the hippocampal formation, subicular area, and entorhinal cortex of rats, all on the same side. The EEG, EOG, and neck EMG were also recorded. Responses due to electrical stimulation of one electrode pair were recorded in the other electrode pairs during slow-wave sleep, paradoxical sleep, and arousal. The stimuli were single, constant current pulses once every 5 sec. Most responses did not change with different states of consciousness. All responses which were smaller during paradoxical sleep than during slow-wave sleep were also small during arousal. Most changes were in this category. All of the responses which were larger during paradoxical sleep than in slow-wave sleep were the same in arousal and slow-wave sleep. Responses in hippocampus or fascia dentata from stimulation of other parts of these structures often changed, usually decreasing during paradoxical sleep and arousal. Responses in subiculum, presubiculum, or entorhinal cortex from stimulation of hippocampus or fascia dentata usually changed, usually decreasing with paradoxical sleep and arousal. Responses in entorhinal cortex or presubiculum from stimulation of subiculum increased in paradoxical sleep. Responses in fornix and CA, from stimulation of presubiculum decreased in paradoxical sleep. An important negative finding was that no responses due to stimulation of entorhinal cortex changed in different states of consciousness. No clear correlation of the changes with phasic phenomena of paradoxical sleep was seen.