A code for ponto-geniculo-occipital wave (PGO)

A mechanism of generation of pontine-geniculo-occipital waves (PGO) has been addressed by intra- or extra-cellular recordings from pontine giganto-cellular neurons (PPRF) during various types of vestibular stimulation (cat). PPRF neurons were identified that responded with spike trains ((mean) 8 spike per sec). Statistical treatments of interspike interval and autocorrelation histograms revealed that the response was basically nonrandom. The same PPRF neurons also responded to medium frequency stimulation of excitatory pulse trains released from the medial vestibular nuclei, mainly in cats with enucleated nucleus interstitialis of Cajal and Nucleus Darkschewitsch (NiC, ND) (inhibitory interneurons). Medium frequency MVN activity evoked (generated by REM or by infusion of acetylcholine) the inhibitory activity of interneurons in intact cats. With decreased MVN activity, the inhibition ceased and excitatory pulses were again generated. During REM this process resulted in a cyclic activity with recurring peak-maximums at 3 to 3.5 sec intervals. This cyclic second order vestibular activity reached the PPRF through the medial longitudinal fasciculus together with several other descending vestibular impulses. The special PPRF neurons selectively respond to the cyclic stimuli of second order vestibular nucleus origin with release of the pontine PGO waves. The regularity of the spikes and the interburst intervals are under the control of two different types of pacemaker neurons located near the midline of pons anterior to the PPRF region with 125 msec and 3 to 3.5 sec interpeak intervals respectively. The results suggest that the vestibular system is one of the structures responsible for encoding the PGO waves.