Pontine gigantocellular field neuron activity time-locked with the PGO waves in the transitional phase of sleep in the cat.

The extracellularly recorded discharge of pontine gigantocellular tegmental field (FTG) neurons was studied in the cat during the transitional phase of sleep (TPS), which signifies in this study the shift from slow wave sleep (S) to paradoxical sleep (PS). The first appearance of pontogeniculo-occipital (PGO) waves, which were led off from the lateral geniculate nucleus, indicated the start, and the decrease of neck muscle tone the end of TPS. TPS was chosen because most PGO waves were then isolated and thus suitable for comparison with the discharge of neurons, which were localized to the antero-lateral part of the FTG. In order to analyze the possible role of these neurons in the control of PGO wave activity, the mean discharge rate of FTG neurons was studied in greater detail during 200 ms periods before and after the onset of each isolated PGO wave. Most FTG neurons discharged phasically and their activity was closely related to isolated PGO waves, so that the highest rate of unit discharge occurred within 40 ms period after the onset of the isolated PGO wave, being time-locked with its first deflection.