Vestibulocollic reflexes: normal values and the effect of age

OBJECTIVES To define normal values and examine the influence of ageing on vestibulocollic reflexes (VCR). METHODS Vestibulocollic responses to 100 dB (normal hearing level; NHL) clicks, forehead taps and galvanic stimulation were measured in 70 healthy adults aged 25-85 years. RESULTS Click- and galvanic-evoked responses were present bilaterally in all subjects below 60. Average click-evoked response amplitudes decreased with age, with a pronounced decline of 25-30% per decade from the 6th decade. The average click thresholds increased from 85 dB in the third decade to 96.5 dB in the 8th and 9th decades. Average galvanic-evoked VCR amplitudes decreased sharply from the seventh decade. Tap-evoked reflex amplitudes showed a milder decrease. When side to side differences in amplitude were expressed as asymmetry ratios (AR) in subjects below the age of 60, values of up to 35 and 46% were obtained for click amplitudes corrected and uncorrected for background electromyogram (EMG), up to 61% for both corrected and uncorrected tap response amplitudes, and up to 41 and 55% for corrected and uncorrected galvanic-evoked responses. CONCLUSIONS A normative range of values can be specified for click- and galvanic-evoked VCRs for subjects up to the age of 60. Click- and galvanic-evoked VCR amplitudes decrease rapidly thereafter while tap-evoked responses are less affected. These changes are probably due to morphological changes in the vestibular system occurring with ageing and are more marked than in several previous reports of age-related changes in caloric responses and vestibulo-ocular reflexes.