Relations of single semicircular canals to the pontine reticular formation

The effects of afferent vestibular impulses on single pontine reticular formation units and on a small filament of the IIIrd cranial nerve were recorded with tungsten microelectrodes in 40 curarized guinea pigs. Single shock and repetitive electrical stimulations were applied by means of stimulating electrodes inserted bilaterally into the perilymphatic space of single ampullae of the anterior and lateral semicircular canals. The reticular unitary response consisted mainly in excitation of the resting discharge rate: most units showed vestibular convergence being affected by separate stimulation of the single 4 ampullae. The reticular evoked field and unitary potentials accounted for latency values ranging from 0.3 to 2.5 msec. As for the early latencies, they can be interpreted as responses mediated by direct vestibuloreticular fibers. A delimited vestibular projection field in the paramedian pontine reticular formation was not identified.