Article

Asymmetric responses to rotation at high frequencies in central vestibular neurons of the alert cat.

Division of Neurology, Department of Medicine, University of Toronto, Toronto, ON, Canada M5T 2S8.
Brain Research (Impact Factor: 2.83). 05/2004; 1005(1-2):137-53. DOI: 10.1016/j.brainres.2004.01.042
Source: PubMed

ABSTRACT The horizontal rotatory vestibulo-ocular reflex (VOR) stabilizes gaze by moving the eyes at an angular velocity proportional to head velocity, and can accomplish this for a broad range of frequencies and amplitudes of head motion. Rotation at 5 Hz and above may be processed differently than lower frequencies by the VOR network. We recorded discharges and calculated spike densities of a small sample of vestibular neurons in alert cats during low-velocity rotation at frequencies up to 8 Hz. At high frequencies, we found both vestibular-only (V-only) and eye-movement-sensitive (EM) cells that generated asymmetric output signals. Asymmetry was primarily of the cutoff type, i.e., changes in spike density were smallest for rotation in the inhibitory direction. Most cells were identified as secondary neurons. The mean spike density was 23 sp/s, which was lower than previously reported in vestibular neurons of monkeys. A few neurons had very high sensitivities, associated with phase-locking, to rotation at high frequencies. In general, vestibular neurons carried a high-pass-filtered version of rotational signals. When synaptic inputs from the vestibular commissure were quantified, we found that the immediate change in probability of firing due to commissural vestibular input was inversely correlated with the degree of high-pass filtering. At high frequencies, increased asymmetry and phase-locking occurred in some neurons. A small number of neurons responded with increased probability of firing to both directions of rotation. Together, these observations suggest that high frequencies of rotation may be encoded differently than low frequencies by central vestibular neurons in alert animals.

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Available from: Adrian J Priesol, Feb 01, 2014
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    • "c o m w w w. e l s ev i e r. c o m / l o c a t e / b r a i n r e s many secondary vestibular neurons display cutoff responses (i.e., are silenced during rotation in their off-directions), even at low speeds (Melvill Jones and Milsum, 1970; Newlands and Perachio, 1990a; Escudero et al., 1992; Chen-Huang and McCrea, 1999; Broussard et al., 2004). In awake cats, most central vestibular neurons consistently have asymmetric responses to sinusoidal rotation (Broussard et al., 2004). Primary afferents from the semicircular canal endorgans also are not purely linear in their response characteristics, and irregularly-firing afferents can be silenced during contralateral rotation (Dickman and Correia, 1989; Hullar et al., 2005). "
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