Age-Related Impairment of Hand Movement Perception Based on Muscle Proprioception and Touch.

Impairment in fine hand motor dexterity is well established in older people, yet little is known, about the impaired perception of hand movement in the elderly. Only an age-related increase in movement detection threshold has been reported. Perception of hand movements relies on multiple sensory information, including touch and muscle proprioception. The present study aims to investigate to what extent aging impacts the ability to perceive hand movements accurately and whether this impairment is from a muscle touch and/or tactile origin. To disentangle proprioception and touch, we used specifically designed stimuli: a mechanical vibration applied to the wrist muscle tendon and a tactile-textured disk rotating under the participant's hand, respectively. These two stimuli elicited illusions of hand rotations in two groups of young (20-30 years) and older (65-75 years) participants. Psychophysical testing showed that velocity discrimination thresholds of tactile and proprioceptive illusions were about twice lower in the young, than the older group. Also, relatively small isometric contractions were involuntarily elicited in wrist muscles during the illusions in both groups, but this motor response was positively correlated with the discrimination performance of the young, but not the older, participants. The present results show that muscle proprioception and touch are both functionally affected in kinesthesia after 65 years old, with a more pronounced alteration for muscle proprioception. This alteration in discriminative ability is likely due to impairment in the accurate encoding of the kinematic properties of hand movements. The possible central vs peripheral origin of these perceptive-motor changes with aging is discussed.