Abstract
Tendon vibration has multiple effects within the central nervous system, with proprioceptive illusions being one of the most studied. During tendon vibration, muscle spindle afferents (primarily Ia) demonstrate an increase in firing rates locked to the vibration frequency. This increased muscle spindle activity is interpreted as the muscle being longer than it is. For example, if the biceps are vibrated during elbow extension to a target position, a participant will undershoot the target as the increased spindle activity is interpreted as the arm being more extended. Recently, noisy tendon vibration (NTV) has been used to assess the frequency characteristics of the Ia afferent pathway during standing balance, without inducing a directional shift in the centre of pressure as would be expected with periodic vibration. This implies that NTV does not induce proprioceptive illusions. To test this directly, we examined the effects of periodic and noisy vibration on an upper limb targeting task. Participants made wrist extension movements to targets while wrist flexor tendons were vibrated with periodic (20 - 100 Hz; 20 Hz increments) or noisy (10-100 Hz) vibration. Results indicate that NTV elicited proprioceptive illusions like periodic vibration. Additionally, with periodic vibration, illusion magnitude depended on vibration frequency. Future studies using NTV should consider that the technique does not only test the Ia pathway but also results in proprioceptive illusions and changes in the stretch reflex gain (Eschelmuller et al., 2021).Acknowledgments: Supported by Natural Sciences and Engineering Research Council of Canada