Behavioral and psychophysical characterization of proprioceptive impairment in healthy aging: a hyper-illusory experience of movement

Age-related deterioration of the sensorimotor system can impair proprioception. This study aimed to characterize age-related changes in the sense of position and movement. Three experiments involved two groups of participants (29 young adults and 26 older adults) to i) evaluate the performance in a position matching task (Experiment 1), ii) assess the perception and reproduction of an illusory movement evoked by proprioceptive stimulation (mechanical muscle-tendon vibration) (Experiment 2), and iii) investigate the ability to discriminate between illusory movements evoked with different frequencies of stimulation (Experiment 3)). No significant differences were found between young and older in the position matching task performance in Experiment 1. In contrast, in Experiment 2, older adults manifested a hyper-illusory experience of movement eliciting perception of wider and faster movements than young. Furthermore, psychometric analysis indicated a reduced ability in older adults to discriminate among different illusory experiences. This study provides the first evidence that aging is associated with an increase in illusory experiences in the elderly, a phenomenon likely related to changes in the mechanisms that control the responses of the Ia muscle spindles fibers and the central processing of the afferent signals.