Sleep recordings from limbic structures in man.

Electrical activity from limbic structures was recorded in epileptic patients carrying chronically implanted electrodes. Power spectra and ‘compressed spectral arrays’ were also calculated. Low frequencies are dominant in the limbic structures. During slow sleep, in all structures, their EEG amplitude and spectral intensity increase. A clear decrease occurs when REM stage is scored. Stages 2–4 are not sharply distinguishable. EEG and spectral differences are found between the neocortex and the limbic structures among the limbic structures and within the same structure. Frequencies from the hippocampal pes during REM stage are completely different from those obtained during wakefulness and slow sleep. On the contrary, the spectrum of the uncus shows the least variations with the time. Fast activity and spindles are mainly seen in the hippocampal pes. Spindles appear during stage 1 and REM. Steady activity at 5 cps similar to the classical Θ-rhythm was seen in a patient, 4 mm above the hippocampal pes. In one single sleep cycle a typical power spectrum was obtained upon occurrence of REM.