External inferior colliculus integrates trigeminal and acoustic information: Unit responses to trigeminal nucleus and acoustic stimulation in the guinea pig

Abstract

The external nucleus of the inferior colliculus (ICx) receives ascending projections from both auditory and somatosensory nuclei [L.M. Aitkin, H. Dickhaus, W. Schult, M. Zimmermann, External nucleus of inferior colliculus: auditory and spinal somatosensory afferents and their interactions, J. Neurophysiol. 41 (1978) 837–847; L.M. Aitkin, C.E. Kenyon, P. Philpott, The representation of the auditory and somatosensory systems in the external nucleus of the cat inferior colliculus, J. Comp. Neurol. 196 (1981) 25–40]. In the guinea pig, both the spinal trigeminal nucleus (TN) and the cochlear nucleus converge in the ventrolateral region of ICx [J. Zhou, S.E. Shore, Convergence of spinal trigeminal and cochlear nucleus projections in the inferior colliculus of the guinea pig, J. Comp. Neurol., in press]. We investigated the function of trigeminal-collicular pathways by electrically stimulating the TN while recording unit responses from ICx. Pairing electrical stimulation with acoustic stimuli allowed us to investigate the function of converging auditory and somatosensory inputs, i.e. multisensory integration. Unit responses were recorded from ICx using a multi channel, single shank electrode. Electrical stimulation of the TN produced small changes above or below spontaneous rate, but resulted in significant suppression or enhancement of sound-evoked responses. Multisensory integration has been demonstrated in the dorsal cochlear nucleus (DCN) [S.E. Shore, Multisensory integration in the dorsal cochlear nucleus: unit responses to acoustic and trigeminal ganglion stimulation, Eur. J. Neurosci. 21 (2005) 3334–3348], superior colliculus [M.A. Meredith, B.E. Stein, Visual, auditory, and somatosensory convergence on cells in superior colliculus results in multisensory integration, J. Neurophysiol. 56 (1986) 640–662] and sensory cortices [P.J. Laurienti, M.T. Wallace, J.A. Maldjian, C.M. Susi, B.E. Stein, J.H. Burdette, Cross-modal sensory processing in the anterior cingulate and medial prefrontal cortices, Hum. Brain Mapp. 19 (2003) 213–223] and may play a role in plasticity that occurs after sensory deprivation.