Spatial distribution of semicircular canal nerve evoked monosynaptic response components in frog vestibular nuclei

Most second-order vestibular neurons receive a canal-specific monosynaptic excitation, although the central projections of semicircular canal afferent s overlap extensively. This remarkable canal specificity prompted us to stu dy the spatial organization of evoked field potentials following selective stimulation of individual canal nerves. Electrically evoked responses in th e vestibular nuclei were mapped systematically in vitro. Constructed activa tion maps were superimposed on a cytoarchitectonically defined anatomical m ap. The spatial activation maps For pre- and postsynaptic response componen ts evoked by stimulation of a given canal nerve were similar. Activation ma ps for monosynaptic inputs from different canals tended to show a different ial distribution of their peak amplitudes, although the overlap was conside rable. Anterior vertical canal signals peaked in the superior vestibular nu cleus, posterior vertical canal signals peaked in the descending and in the dorsal part of the lateral vestibular nucleus, whereas horizontal canal si gnals peaked in the descending and in the ventral part of the lateral vesti bular nucleus. A similar, differential but overlapping, spatial organizatio n of the canal inputs was described also for other vertebrates. suggesting a crude but rather conservative topographical organization of semicircular canal nerve projections within the vestibular nuclei. Differences in the pr ecision of topological representations between vestibular and other sensory modalities are discussed. (C) 2000 Elsevier Science B.V. All rights reserv ed.