Timing of secondary vestibular neuron responses to a range of rotational head movements |
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Authors: | Jan E Holly Gin McCollum |
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Institution: | (1) Department of Mathematics and Computer Science, Colby College, Waterville, ME 04901, USA, US;(2) Robert S. Dow Neurological Sciences Institute, 1120 N.W. 20th Avenue, Portland, OR 97209–1595, USA, US |
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Abstract: | Secondary vestibular neurons exhibit a wide variety of responses to a head movement, with the response of each secondary
neuron depending upon the particular primary afferents converging onto it. A single head movement is thereby registered in
a distributed manner. This paper focuses on implications of afferent convergence to the relative timing of secondary neuron
response modulation during rotational movements about a combination of horizontal axes. In particular, the neurons of interest
are those that receive input from afferents innervating the vertical semicircular canals, and the movements of interest are
those that have a sinusoidal component about one vertical canal axis and a sinusoidal component about another, approximately
orthogonal, vertical canal axis. Under these conditions, the present research shows that it is possible for two or more secondary
neurons to have a different relative timing of response (i.e., different relative phase of the periodic modulation in firing
rate) for different head movements, and for the neurons to switch their order of response for different movements. For particular
head movements, those same neurons will respond in phase. From the point of view of the nervous system, the relative timing
of neuron responses may tell which movement is taking place, but with certain restrictions as discussed in the present paper.
Shown here is that, among those head movements for which the two components of rotation may be at any phase relative to one
another and have any relative amplitude, an in-phase response of just two neurons cannot identify a single motion. Two neurons
that respond in phase for one motion must respond in phase for an entire range of motions; all motions in that range are thus
response-equivalent, in the sense that the pair of neurons cannot distinguish between the two motions. On the other hand,
an in-phase response of three neurons can identify a single motion, for certain patterns of primary afferent convergence.
Received: 16 December 1996 / Accepted in revised form: 3 April 1998 |
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