CORRELATED FIRING OF HIPPOCAMPAL NEURON PAIRS IN SLEEP AND WAKEFULNESS

Temporal patterns of firing in pairs of hippocampal neurons were studied in relation to behavioral states in the cat, using cross correlation techniques. These units were recorded simultaneously by a single microelectrode. During deep sleep with cortical high-voltage slow-wave activity, a high correlation was observed in the patterning of firing in the neuronal pairs. There was a high probability of correlated firing within a short time (for example, 5 msec) with an increased chance of concurrent appearance of long inactive periods in the neuronal pairs. When the behavioral state shifted from sleep to wakefulness, patterns of the two spike trains showed a reduced correlation, with concomitant decrease in the probability of correlated firing. In this state, though the long inactive periods appeared in individual neurons, they did not occur simultaneously in adjacent neurons. In behavioral arousal or in REM sleep, which are characterized by hippocampal theta activity, firing patterns in neuronal pairs showed minimal correlation. The probability of correlated firing fell to chance levels. © 1969.