Search

International audience

International audience; To perceive self-hand movements, the central nervous system (CNS) relies on multiple sensory information mainly derived from vision, touch, and muscle proprioception. Using psychophysical approaches, this study investigated how and to what extent the CNS relies on these sensory systems to build kinesthetic percepts when they all decline such as when aging. Illusory movement perceptions were induced by stimulating these three sensory modalities either separately or concomitantly. The perceptual responses reported by 19 healthy elderly adults (60-82 yrs) were compared to those of 12 young adults. Results suggest that reliance on sensory inputs for kinesthetic purposes is profoundly reshaped as early as 60 years old. Older people rely more on visual and tactile afferents for perceiving self-hand movements than younger adults. This could be due to a relative greater muscle proprioception impairment.

International audience; Unlike age-related brain changes linked to motor activity, neural alterations related to self-motion perception remain unknown. Using fMRI data, we investigated age-related changes in the central processing of somatosensory information by inducing illusions of right-hand rotations with specific proprioceptive and tactile stimulation. Functional connectivity during resting-state (rs-FC) was also compared between younger and older participants. Results showed common sensorimotor activations in younger and older adults during proprioceptive and tactile illusions, but less deactivation in various right frontal regions and the precuneus were found in the elderly. Older participants exhibited a less-lateralized pattern of activity across the primary sensorimotor cortices (SM1) in the proprioceptive condition only. This alteration of the interhemispheric balance correlated with declining individual performance in illusion velocity perception from a proprioceptive, but not a tactile, origin. By combining task-related data, rs-FC and behavioral performance, this study provided consistent results showing that hand movement perception was altered in the elderly, with a more pronounced deterioration of the proprioceptive system, likely due to the breakdown of inhibitory processes with aging. Nevertheless, older people could benefit from an increase in internetwork connectivity to overcome this kinesthetic decline.

International audience; Optimal visuotactile integration for velocity discrimination of self-hand movements. Illusory hand movements can be elicited by a textured disk or a visual pattern rotating under one's hand, while proprioceptive inputs convey immobility information (Blanchard C, Roll R, Roll JP, Kavounoudias A. PLoS One 8: e62475, 2013). Here, we investigated whether visuotactile integration can optimize velocity discrimination of illusory hand movements in line with Bayesian predictions. We induced illusory movements in 15 volunteers by visual and/or tactile stimulation delivered at six angular velocities. Participants had to compare hand illusion velocities with a 5°/s hand reference movement in an alternative forced choice paradigm. Results showed that the discrimination threshold decreased in the visuotactile condition compared with unimodal (visual or tactile) conditions, reflecting better bimodal discrimination. The perceptual strength (gain) of the illusions also increased: the stimulation required to give rise to a 5°/s illusory movement was slower in the visuotactile condition compared with each of the two unimodal conditions. The maximum likelihood estimation model satisfactorily predicted the improved discrimination threshold but not the increase in gain. When we added a zero-centered prior, reflecting immobility information, the Bayesian model did actually predict the gain increase but systematically overestimated it. Interestingly, the predicted gains better fit the visuotactile performances when a proprioceptive noise was generated by covibrating antagonist wrist muscles. These findings show that kinesthetic information of visual and tactile origins is optimally integrated to improve velocity discrimination of self-hand movements. However, a Bayesian model alone could not fully describe the illusory phenomenon pointing to the crucial importance of the omnipresent muscle propriocep-tive cues with respect to other sensory cues for kinesthesia. NEW & NOTEWORTHY The present study demonstrates, for the first time, that kinesthetic information of visual and tactile origins are optimally integrated (Bayesian modeling) to improve velocity discrimination for self-hand movement. We used an original paradigm consisting of similar illusory hand movements induced through visual and tactile stimulation. By testing the role of other sources of information favoring nonmoving hand perception, we also highlight the key contribution of the omnipresent muscle proprioceptive information and its overweighting for kinesthesia.

International audience; It is well known that kinesthetic illusions can be induced by stimulation of several sensory systems (proprioception, touch, vision...). In this study we investigated the cerebral network underlying a kinesthetic illusion induced by visual stimulation by using functionalmagnetic resonance imaging (fMRI) in humans. Participants were instructed to keep their hand still while watching the video of their own moving hand (Self Hand) or that of someone else's moving hand (Other Hand). In the Self Hand condition they experienced an illusory sensation that their hand was moving whereas the Other Hand condition did not induce any kinesthetic illusion. The contrast between the Self Hand and Other Hand conditions showed significant activation in the left dorsal and ventral premotor cortices, in the left Superior and Inferior Parietal lobules, at the right Occipito-Temporal junction as well as in bilateral Insula and Putamen. Most strikingly, there was no activation in the primary motor and somatosensory cortices, whilst previous studies have reported significant activation in these regions for vibrationinduced kinesthetic illusions. To our knowledge, this is the first study that indicates that humans can experience kinesthetic perception without activation in the primarymotor and somatosensory areas. We conclude that under some conditions watching a video of one's ownmoving hand could lead to activation of a network that is usually involved in processing copies of efference, thus leading to the illusory perception that the real hand is indeed moving.