In this study, we examined age-related effects upon modulation of the VOR with visual and imaginary targets during sinusoidal harmonic acceleration. Eight young (< 30 years) and 5 elderly (> 65 years) subjects were tested using sinusoidal whole-body rotation at 0.025 Hz, 0.1 Hz, and 0.5 Hz. Peak velocity for all trials was 50 degrees/s. Mean VOR gain and phase were calculated under the following paradigms: mental tasking (in darkness), visual enhancement (earth-fixed visual target), visual suppression (chair-fixed visual target), mental enhancement (earth-fixed imaginary target), and mental suppression (chair-fixed imaginary target). Test results from VOR trials in darkness with mental tasking were used as a reference for comparing results obtained from the various paradigms. Our results indicate significant changes in VOR gain for both age groups compared to VOR with mental tasking for the visually enhanced, visually suppressed, and mentally suppressed paradigms at all three frequencies. Neither group showed significant enhancement of VOR gain with an earth-fixed imaginary target at any frequency. Both groups were nearly equal in their abilities to enhance and suppress VOR gain under the visual paradigms. Younger subjects showed a significantly greater degree of gain suppression at 0.5 Hz than the older group for the mental suppression paradigm. VOR phase tended toward zero during the visual paradigms for both groups at all frequencies. For the mental imagery paradigms, VOR phase resembled values for VOR with mental tasking in the younger group at all three frequencies and in the older group at all but 0.1 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMedDate not supplied

Head slippage during broad-frequency rotational chair testing.

Broad-frequency rotational chair testing is employed in clinical and research settings to evaluate the response of the vestibulo-ocular reflex (VOR) over a range of frequencies. Accurate computation of the gain and phase of the VOR is dependent upon the assumption that the subject's head is rigidly coupled to the rotating chair over the range of frequencies employed. We tested this assumption by examining head slippage in 20 normal subjects using a standard rotational chair over the frequency range 0.025 to 2 Hz. Measurements were made with the subjects' head optimally restrained according to our standard clinical protocol and with the head minimally restrained. Head slippage was expressed as gain and phase of the head with respect to the chair. Computation of these parameters was made by comparing the signal received from a biteblock-mounted rate sensor rigidly coupled to the skull with that of the chair's tachometer. We found highly significant slippage of the head with respect to the chair occurred at 0.5, 1 and 2 Hz, even with the head optimally restrained, leading to increased gain and a phase lag. Gain and phase were highly variable for both conditions at 2 Hz indicating inadequate head fixation using our methods. Below 0.5 Hz, minimal head slippage occurred whether the head was restrained or simply rested against a contoured headrest. Consideration of these results may lead to changing some practices currently employed in broad-frequency rotational chair testing at frequencies of 0.5 Hz and above.

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PubMedDate not supplied

Comparison of manual whole-body and passive and active head-on-body rotational testing with conventional rotary chair testing.

New methods of rotational testing of the vestibulo-ocular reflex (VOR) using manually generated or patient-generated sinusoidal head movements have recently been advocated for clinical use in circumstances where conventional rotary chair testing methods are not feasible. However, studies seeking to provide evidence for the validity of these methods by comparing their results with an accepted "gold-standard" have been conspicuously absent in the literature. In this study, we compared results for VOR gain, phase, and asymmetry obtained using whole-body and head-on-body rotational stimuli with those obtained by conventional rotary chair testing in 35 subjects with either unilateral or bilateral vestibular deficits over the range of frequencies from 0.025 Hz to 1 Hz. Our results provide evidence for the validity of manual whole-body and active and passive head-on-body rotational testing methods by demonstrating excellent agreement between each of these and conventional rotational chair testing for VOR gain, phase, and asymmetry within the frequency range studied. Small differences at specific-paradigm datapoints are likely secondary to subtle limitations of our experimental design. With further refinement, we expect the new methods will be useful adjuncts for evaluating patients with vestibular complaints in selected clinical situations.

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