Animal studies suggest that the vestibular system autoregulates its sensitivity in response to prolonged low- or high-intensity motion in order to maintain an optimal working range. In humans, corresponding attenuations of vestibular responses after prolonged high-intensity motion exposure have been demonstrated. Here we explored whether a complementary increase in human vestibular sensitivity can be induced by motion conditioning at low-intensity, subliminal amplitudes. In 9 healthy subjects, vestibular perceptual thresholds for translational motion along the inter-aural (IA) axis were determined in a direction-recognition task at baseline as well as immediately and 20-min after subliminal motion stimulation. The subliminal conditioning stimulus consisted of a 20-min 1 Hz sinusoidal IA translation at an amplitude of 70% of each subject's baseline IA threshold (2.09 ± 0.78 cm/s2 peak acceleration). In a second set of experiments, we tested whether IA conditioning also influences perceptual thresholds for yaw rotations. Immediately after conditioning, IA thresholds were effectively lowered (p = 0.002; mean reduction: 28.8 ± 4.5%). These improvements were transient and thresholds had returned to baseline level 20 min after conditioning (p = 0.015). Vestibular sensitivity for yaw rotations remained on average unaltered after IA conditioning indicating that sensitizing effects might be selective for the end-organ-specific vestibular pathways being stimulated during conditioning. These findings demonstrate that human vestibular sensitivity can be enhanced by subliminal sensory conditioning, similar to sensitizing effects observed in other sensory modalities. Conditioning-induced sensitization of vestibular responses may be an effective treatment for decrements in vestibular sensitivity in the elderly and patients with vestibular hypofunction.
Keywords: direction-recognition thresholds homeostatic plasticity subliminal conditioning vestibular perception vestibular stimulation