Visuomotor adaptation across the lifespan.

Being able to adapt our movements to changing circumstances allows people to maintain performance across a wide range of tasks throughout life, but it is unclear whether visuomotor learning abilities are fully developed in young children and, if so, whether they remain stable in the elderly. There is limited evidence of changes in motor adaptation ability throughout life, and the findings are inconsistent. Therefore, our goal was to compare visuomotor learning abilities throughout the lifespan. We used a shorter, gamified experimental task and collected data from participants in 5 age groups. Young children (M = 7 years), older children (M = 11 years), young adults (M = 20 years), adults (M = 40 years) and older adults (M = 67 years) adapted to a 45° visuomotor rotation in a centre-out reaching task. Across measures of rate of adaptation, extent of learning, rate of unlearning, generalization, and savings, we found that all groups performed similarly. That is, at least for short bouts of gamified learning, children and older adults perform just as well as young adults.

Sensing hand position in Ehlers-Danlos syndrome.

PURPOSE: To explore the effect of joint hypermobility on acuity, and precision, of hand proprioception. MATERIALS AND METHODS: We compared proprioceptive acuity, and precision, between EDS patients and controls. We then measured any changes in their estimates of hand position after participants adapted their reaches in response to altered visual feedback of their hand. The Beighton Scale was used to quantify the magnitude of joint hypermobility. RESULTS: There were no differences between the groups in the accuracy of estimates of hand location, nor in the visually induced changes in hand location. However, EDS patients' estimates were less precise when based purely on proprioception and could be partially predicted by Beighton score. CONCLUSIONS: EDS patients are less precise at estimating their hand's location when only afferent information is available, but the presence of efferent signalling may reduce this imprecision. Those who are more hypermobile are more likely to be imprecise.

Proprioceptive precision is impaired in Ehlers-Danlos syndrome.

It has been suggested that people with Ehlers-Danlos syndrome (EDS), or other similar connective tissue disorders, may have proprioceptive impairments, the reason for which is still unknown. We recently found that EDS patients were less precise than healthy controls when estimating their felt hand's position relative to visible peripheral reference locations, and that this deficit was positively correlated with the severity of joint hypermobility. We further explore proprioceptive abilities in EDS by having patients localize their non-dominant left hand at a greater number of workspace locations than in our previous study. Additionally, we explore the relationship between chronic pain and proprioceptive sensitivity. We found that, although patients were just as accurate as controls, they were not as precise. Patients showed twice as much scatter than controls at all locations, but the degree of scatter did not positively correlate with chronic pain scores. This further supports the idea that a proprioceptive impairment pertaining to precision is present in EDS, but may not relate to the magnitude of chronic pain.

The effect of visuomotor adaptation on proprioceptive localization: the contributions of perceptual and motor changes.

Reaching movements are rapidly adapted following training with rotated visual feedback of the hand (motor recalibration). Our laboratory has also found that visuomotor adaptation results in changes in estimates of felt hand position (proprioceptive recalibration) in the direction of the visuomotor distortion (Cressman and Henriques 2009, 2010; Cressman et al. 2010). In the present study, we included an additional method for measuring hand proprioception [specifically, proprioceptive-guided reaches of the unadapted (left) hand to the robot-guided adapted (right) hand-target] and compared this with our original perceptual task (estimating the felt hand position of the adapted hand relative to visual reference markers/the body midline), as well as to no-cursor reaches with the adapted hand (reaching to visual and midline-targets), to better identify whether changes in reaching following adaptation to a 50° rightward-rotated cursor reflect sensory or motor processes. Results for the proprioceptive estimation task were consistent with previous findings; subjects felt their hand to be aligned with a reference marker when it was shifted approximately 4° more in the direction of the visuomotor distortion following adaptation compared with baseline conditions. Moreover, we found similar changes in the proprioceptive-guided reaching task such that subjects misreached 5° in the direction of the cursor rotation. However, these results were true only for proprioceptive-guided reaches to the adapted hand, as reaches to the body midline were not affected by adaptation. This suggests that proprioceptive recalibration is restricted to the adapted hand and does not generalize to the rest of the body; this truly reflects a change in the sensory representation of the hand rather than changes in the motor program. This is in contrast to no-cursor reaches made with the adapted hand, which show reach after-effects for both visual targets and the midline, suggesting that reaches with the adapted hand reflect more of a change in the motor system. Our results also shed light on previous studies that may have misattributed these sensory and motor changes.

Proprioceptive sensitivity in Ehlers-Danlos syndrome patients.

Reaching movements are rapidly adapted following training with rotated visual feedback of the hand. Our laboratory has also found that this visuomotor adaptation results in changes in estimates of felt hand position (proprioceptive recalibration) in the direction of the visuomotor distortion (Cressman and Henriques in J Neurophysiol 102:3505-3518, 2009; Cressman et al. in Exp Brain Res 205:533-544, 2010). In the current study, we investigated proprioceptive acuity and proprioceptive recalibration in a group of individuals with Ehlers-Danlos syndrome (EDS), a degenerative condition associated with collagen malformation. Some studies have suggested that these patients may have proprioceptive impairments, but the exact nature of the impairment is unclear (Rombaut et al. in Clin Rheumatol 29:289-295, 2010a). In this study, we measured the ability of EDS patients to estimate their felt hand position and tested whether these estimates changed following visuomotor adaptation. We found EDS patients were less precise in estimating their felt hand position in the peripheral workspace compared to healthy controls. Despite this poorer sensitivity, they recalibrated hand proprioception to the same extent as healthy controls. This is consistent with other populations who experience proprioceptive deficits (e.g. the elderly, Parkinson's disease patients), suggesting that sensory noise does not influence the extent of either motor or sensory plasticity.