Neuronal activity in the lateral vestibular necleus of the cat. IV. Postsynaptic potentials evoked by stimulation of peripheral somatic nerves.

The synaptic input to Deiters neurones evoked by stimulation of peripheral somatic nerves was measured by intracellular recordings. EPSPs with broad receptive fields and latencies which indicate polysynaptic connexions were commonly evoked from the FRA. In other cells, low threshold cutaneous afferents were effective at rather short latencies suggesting oligosynaptic connexions from fast ascending fibres. One example was found of EPSPs due to low threshold muscle afferents. IPSPs due to climging fibre activation of Purkinje cells as observed in most of the neurones were evoked by cutaneous volleys above 1.5-2.0T and muscle volleys above 5T (above 3-3.5T in case of Q). Often, IPSPs were evoked by stimulation of nerves, to the segmental level of which the the vestibulospinal neurone under investigation projected. A small proportion of cells received short latency IPSPs involving direct fast mossy fibre tracts, which were evoked from low threshold cutaneous afferents. IPSPs due to polysynaptic mossy fibre activation of Purkinje cells were evoked from the FRA bilaterally and from ipsilateral cutaneous afferents at 1.5-2.0T ("prolonged inhibition"). Prolonged excitatory/inhibitory events mediated by mossy fibre pathways may be involved in quadruped locomotion or other processes making use of a broad motor integration.