Early Blindness Limits the Head-Trunk Coordination Development for Horizontal Reorientation

During locomotion, goal-directed orientation movements in the horizontal plane require a high degree of head-trunk coordination. This coordination is acquired during childhood. Since early visual loss is linked to motor control deficits, we hypothesize that it may also affect the development of head-trunk coordination for horizontal rotations. However, no direct evidence exists about such a deficit. To assess this hypothesis, we tested early blind and sighted individuals on dynamic sound alignment through a head-pointing task with sounds delivered in acoustic virtual reality. Participants could perform the head-pointing with no constraints, or they were asked to immobilize their trunk voluntarily. Kinematics of head and trunk were assessed individually and with respect to each other, together with spatial task performance. Results indicated a head-trunk coordination deficit in the early blind group; yet, they could dampen their trunk movements so as not to let their coordination deficit affect spatial performance. This result highlights the role of vision in the development of head-trunk coordination for goal-directed horizontal rotations. It also calls for clarification on the impact of the blindness-related head-trunk coordination deficit on the performance of more complex tasks akin to daily life activities such as steering during locomotion or reaching to targets placed sideways.

Spatial cell firing during virtual navigation of open arenas by head-restrained mice

We present a mouse virtual reality (VR) system which restrains head-movements to horizontal rotations, potentially compatible with multi-photon imaging. We show that this system allows expression of the spatial navigational behaviour and neuronal firing patterns characteristic of real open arenas (R). Place and grid, but not head-direction, cell firing had broader spatial tuning in VR than R. Theta frequency increased less with running speed in VR than in R, while firing rates increased similarly in both. Place, but not grid, cell firing was more directional in VR than R. These results suggest that the scale of grid and place cell firing patterns, and the frequency of theta, reflect translational motion inferred from both virtual (visual and proprioceptive) cues and uncontrolled static (vestibular translation and extra-maze) cues, while firing rates predominantly reflect visual and proprioceptive motion. They also suggest that omni-directional place cell firing in R reflects local-cues unavailable in VR.

Roles of Head, Gaze, and Spatial Orientation in the Production of Oscillopsia

To clarify the factors causing oscillopsia, we investigated head movement, gaze stability, and perception under various situations. High-frequency head movements, whether they were horizontal rotations or passively induced vertical oscillations, produced blurred vision and gaze fluctuations in patients with labyrinthine loss. However, this sensation differed from the oscillopsia perceived during walking, as it did not involve a sensation of oscillation of the surrounding space or a loss of body balance. Although patients with labyrinthine loss showed large irregular head perturbations during stepping, the resultant retinal velocity slips seemed too small to explain oscillopsia. Walking while wearing horizontal reversing prisms produced loss of spatial orientation, dysequilibrium, and instability of vision in normal subjects, which resembled the symptoms found in patients with oscillopsia. The present study suggests that oscillopsia represents a perceptual inability to detect spatial orientation during head or body movements rather than a mere blurring of vision caused by deficient compensation.

Dynamics of Adaptive Change in Human Vestibulo-Ocular Reflex Direction

Adaptive modification of vestibulo-ocular reflex (VOR) direction was characterized in humans by recording vertical and horizontal VOR eye movements during horizontal rotations in darkness at frequencies of 0.05 to 1 Hz before and after exposure to a VOR direction adaptation procedure. This procedure paired yaw horizontal vestibular rotation at 0.25 Hz with synchronous pitch vertical optokinetic motion. Saccades were removed from eye position records and VOR gain and phase were recorded. With an onset time constant of 36 min, the VOR measured during horizontal rotation in complete darkness acquired a vertical component in phase with the optokinetic stimulus presented during adaptation. The amplitude of this newly acquired vertical VOR component was maximal during rotation at the frequency of adaptation; at other frequencies, the amplitude was lower, but still significant. Unlike VOR direction adaptation in cats, the phase of the adaptive VOR component in humans did not show significant leads or lags at test frequencies below or above the adaptation frequency. These data suggest that, like the cat, the human VOR can be directionally adapted, and the pathways involving the adaptive component of the VOR are frequency specific.

Spatial and temporal response properties of the vestibulocollic reflex in decerebrate cats

Vestibulocollic reflex responses of several neck muscles in decerebrate cats were studied during angular rotations of the whole body in a large number of vertical and horizontal rotation planes, at frequencies from 0.07 to 1.6 Hz. Vestibulocollic responses were compared to eye muscle and forelimb muscle vestibular responses. Electromyographic activity was recorded by fine wires inserted in biventer cervicis, complexus, longus capitis, obliquus capitis inferior, occipitoscapularis, rectus capitis major, splenius, lateral rectus, and triceps brachii. At frequencies of approximately 0.5 Hz and above, neck muscle electromyographic response gains were sinusoidal functions of stimulus orientation within a set of vertical or horizontal planes, and a muscle's response phase remained constant across rotation planes, or reversed by 180 degrees. Response patterns at high frequencies were consistent with vestibulocollic reflex activation by semicircular canals through brain circuitry that modifies canal dynamics. At frequencies of approximately 0.5 Hz and above, the stimulus orientation in which a given neck muscle's response was maximal remained nearly constant across frequencies. Thus, we used responses to rotations at high frequencies to calculate axes of maximal response of each muscle in three-dimensional space. Lateral rectus, obliquus, and to a lesser extent, splenius and longus capitus were activated predominantly by horizontal rotations. Biventer was activated predominantly by pitch, triceps predominantly by roll, and complexus, occipitoscapularis, and rectus major significantly excited by rotations in all three coordinate planes. In some cases, at frequencies less than 0.5 Hz, neck muscle response phase varied depending on the vertical plane in which the cat was rotated, and the optimal response plane was poorly defined and varied with frequency. These responses indicated that, at some frequencies, neck muscle activity can result from summation of inputs with differing spatial orientation and dynamics (spatial-temporal convergence). Differences between responses to vertical and horizontal rotations suggested that low-frequency spatial-temporal convergence behavior of the vestibulocollic reflex during vertical rotations was due to convergent semicircular canal and otolith receptor inputs.(ABSTRACT TRUNCATED AT 400 WORDS)