This is a proposal to study somatosensory inputs to the dorsal cochlear nucleus (DCN); these inputs originate in the dorsal column and spinal trigeminal nuclei and project to the granule cell domains of the cochlear nucleus. Somatosensory effects produce rate changes in DCN principal cells which are comparable in magnitude to those produced by sound; current data suggest that the somatosensory input carries information primarily about movement of the pinna. Four projects are proposed to investigate hypotheses suggested by these results. Experiments are conducted in unanesthetized, decerebrate cats or in an awake chronic cat preparation. Methods include recording single unit responses to sound, to electrical stimulation in somatosensory nuclei, and to natural somatosensory stimuli. The first goal is to test the hypothesis that pinna movement is the most potent somatosensory stimulus. We will use a new surgical preparation which keeps the skin and musculature on the ipsilateral side of the head intact. These experiments will differentiate between motion of the pinna, displacement of the pinna, and other somatosensory stimuli to the pinna or the body. Second, the distribution of somatosensory effects within an isofrequency sheet in DCN will be determined. Comparison of somatosensory effects on principal cells in superficial and deep DCN will be done to identify differences expected from the differences in innervation of fusiform and giant cells. Properties of three likely inhibitory interneurons will be studied in order to develop a model of the functional effects of somatosensory inputs in DCN. Interactions of acoustic and somatosensory stimuli will be studied. Third, the properties of the somatosensory projection neurons will be studied by recording from neurons in the dorsal column nuclei that can be antidromically activated from DCN. Their somatosensory responses will be compared to the properties of somatosensory effects in DCN in order to determine what processing is done in the granule cell system of DCN. Fourth, DCN neurons will be recorded in awake animals trained to perform pinna movements in response to external cues (shifting of a sound from one loudspeaker to another). The responses in this preparation will be compared with responses to passive pinna movement in decerebrate preparations to see whether other inputs, possibly correlated with motor commands to the pinna, are also active. Pinna movement will be coupled with sound stimulation in order to search for adaptive plasticity in the responses to either sound or pinna movement; such plasticity is expected from the molecular anatomy of the DCN.
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