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.

Download full-text

Full-text

Available from: Adrian J Priesol, Feb 01, 2014
0 Followers
 · 
72 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A method is developed for representing any communication system geometrically. Messages and the corresponding signals are points in two "function spaces," and the modulation process is a mapping of one space into the other. Using this representation, a number of results in communication theory are deduced concerning expansion and compression of bandwidth and the threshold effect. Formulas are found for the maxmum rate of transmission of binary digits over a system when the signal is perturbed by various types of noise. Some of the properties of "ideal" systems which transmit at this maxmum rate are discussed. The equivalent number of binary digits per second for certain information sources is calculated.
    Proceedings of the IRE 02/1949; 86(1-37):10 - 21. DOI:10.1109/JRPROC.1949.232969
  • [Show abstract] [Hide abstract]
    ABSTRACT: Rotational and translational vestibulo-ocular reflexes (RVOR and TrVOR) function to maintain stable binocular fixation during head movements. Despite similar functional roles, differences in behavioral, neuroanatomical, and sensory afferent properties suggest that the sensorimotor processing may be partially distinct for the RVOR and TrVOR. To investigate the currently poorly understood neural correlates for the TrVOR, the activities of eye movement-sensitive neurons in the rostral vestibular nuclei were examined during pure translation and rotation under both stable gaze and suppression conditions. Two main conclusions were made. First, the 0.5 Hz firing rates of cells that carry both sensory head movement and motor-like signals during rotation were more strongly related to the oculomotor output than to the vestibular sensory signal during translation. Second, neurons the firing rates of which increased for ipsilaterally versus contralaterally directed eye movements (eye-ipsi and eye-contra cells, respectively) exhibited distinct dynamic properties during TrVOR suppression. Eye-ipsi neurons demonstrated relatively flat dynamics that was similar to that of the majority of vestibular-only neurons. In contrast, eye-contra cells were characterized by low-pass filter dynamics relative to linear acceleration and lower sensitivities than eye-ipsi cells. In fact, the main secondary eye-contra neuron in the disynaptic RVOR pathways (position-vestibular-pause cell) that exhibits a robust modulation during RVOR suppression did not modulate during TrVOR suppression. To explain these results, a simple model is proposed that is consistent with the known neuroanatomy and postulates differential projections of sensory canal and otolith signals onto eye-contra and eye-ipsi cells, respectively, within a shared premotor circuitry that generates the VORs.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 07/2001; 21(11):3968-85. · 6.75 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Release probability (P) appears to be a major factor that influences the pattern of transmitter release. At cortical pyramidal axon inputs onto different classes of target cells, very different release patterns are observed, patterns that correlate with release probability. Simplistically, 'low P' synapses display facilitation and augmentation, whereas 'high P' synapses supplied by the same axon exhibit paired-pulse and frequency-dependent depression. Different combinations of factors probably contribute to release probability at different terminals, during development and under different experimental conditions. The recent advances made by molecular biological studies of the release machinery do, however, provide candidate proteins and protein-protein interactions whose differential distributions might be important factors in determining the patterns of transmitter release.
    Trends in Neurosciences 08/2000; 23(7):305-12. DOI:10.1016/S0166-2236(00)01580-0 · 12.90 Impact Factor