Respiratory-related discharge of periaqueductal gray neurons during sleep-waking states.

Extracellular single-unit spontaneous activity was recorded from the periaqueductal gray region (PAG) in undrugged, freely moving cats. Two analyses, cross-correlation histograms and linear regression techniques, were used to examine state relationships of neuronal discharge with respiratory patterning. Of 68 cells recorded, 19 (28%) showed a timing relationship (breath-by-breath dependency), 14 of which were state-dependent. Twenty-three (34%) showed a tonic discharge correlation with the respiratory cycle, and activity of all these cells was state-dependent. These results suggest that a subset of PAG cells may play a role in state-related respiratory patterning.