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Responses of cat prepositus hypoglossi neurons to horizontal angular acceleration

Publication Date
DOI: 10.1016/0306-4522(77)90005-7
  • Pph
  • Rc
  • τD
  • τI
  • Biology


Abstract Responses of single cells in the nucleus prepositus hypoglossi following natural stimulation of the horizontal semicircular canals were studied in cats anesthetized with Ketamine hydrochloride. Prepositus hypoglossi neurons were typically silent or low firing at rest and often showed saccadic-like burst or pause activity. During rotation, type I, II, III and IV vestibular responses were observed in the proportions 26, 70, 2.4 and 1.6%, respectively. Type I and II responses were graded as a function of stimulus intensity, exhibited response null points similar to peripheral horizontal canal neurons and had thresholds and gradients which were comparable, in magnitude, to cells in the vestibular nucleus. Some time constant asymmetries were noted during constant angular acceleration which were enhanced with increasing levels of acceleration and were particularly apparent in cells which had a vestibular evoked nystagmic-like modulation in rate. Sinusoidal acceleration responses were low-skew and consistently modulated (in phase and gain) on a cycle-to-cycle basis despite the asymmetries in time-domain time constants and the occasional saccadic or nystagmic-like activity. Phase-lags between peak unitary discharge and head acceleration for type II prepositus hypoglossi neurons were shifted (by ca. 10–20°) towards larger values at each frequency when compared to type I prepositus hypoglossi neurons or to type I neurons in the vestibular nuclei. These results demonstrate that the nucleus prepositus hypoglossi receives a powerful input from both horizontal canals, and its response is qualitatively similar to cells in the vestibular nuclei. At the quantitative level, however, sufficient differences exist between these two neuronal populations which, when combined with the existing electrophysiological evidence, strongly suggest that the prepositus hypoglossi may be involved in a more complex processing of vestibulo-ocular information.

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