The vertical vestibulo-ocular reflex, and its interaction with vision during active head motion: effects of aging

The effects of aging on the vertical vestibulo-ocular reflex (VOR), and its interactions with vision during active head motion had not been investigated. We measured smooth pursuit, combined eye-head tracking, the VOR, and its visual enhancement and cancellation during active head motion in pitch using a magnetic search coil technique in 21 younger (age < 65) and 10 elderly (age > or = 65) subjects. With the head immobile, subjects pursued a target moving sinusoidally with a frequency range of 0.125 to 2.0 Hz, and with peak target accelerations (PTAs) ranging from 12 to 789 degrees /s(2). Combined eye-head tracking, the VOR in darkness, and its visual enhancement during fixation of an earth-fixed target (VVOR) were measured during active sinusoidal head motion with a peak-to-peak amplitude of 20 degrees at frequencies of 0.25, 0.5, 1.0 and 2.0 Hz. The efficacy of VOR cancellation was determined from VOR gains during combined eye-head tracking. VOR and VVOR gains were symmetrical in both directions and did not change with aging, except for reduced gains of the downward VOR and VVOR at low frequency (0.25 Hz). However, in the elderly, smooth pursuit, and combined eye-head tracking gains and the efficacy of cancellation of the VOR were significantly lower than in younger subjects. In both the young and elderly groups, VOR gain in darkness did not vary with the frequency of active head motion while the gains of smooth pursuit, combined eye-head tracking, and VVOR declined with increasing target frequency. VOR and VVOR performance in the elderly implicates relative preservation of neural structures subserving vertical vestibular smooth eye motion in senescence.