Discharge correlations between neurons in the nucleus parabrachialis medialis during sleep-waking states

Spontaneous activity from simultaneously recorded pairs of neurons in the nucleus parabrachialis medialis (NPBM) was examined in unanesthetized, unrestrained cats during each sleep-waking state. Functional interconnections between pairs of neurons were studied with cross-correlation techniques. A total of neuronal pairs were studied, 38 of which were recorded on separate, but proximal electrodes, and two pairs of which were recorded on the same electrode. Of the 40 pairs of neurons examined, 22 showed short delay (< 4 msec) peaks in the cross correlogram of their spike activity. These correlations tended to be highest in quiet sleep (QS). Increased probability of shared discharge with intermediate delays in the peaks of the cross-correlogram (5-150 msec) was observed in 16 of 40 pairs. The increase in correlation at intermediate delays followed a period of decreased shared activity. Activity at intermediate delay peaks was reduced during rapid eye movement (REM) sleep, and appeared with a shorter delay during that state. Long delay correlation peaks ranging from 0.5 to 6 sec appeared in 23 of 40 neuronal pairs, but only in waking and in REM sleep.