When I am (almost) 64: The effect of normal ageing on implicit motor imagery in young elderlies

• Implicit motor imagery (IMI) depends on premotor/parietal and occipital cortices.
• We compared the IMI skills and associated brain activations of young and elderly subjects.
• Healthy elderlies in their sixties had qualitatively preserved implicit motor imagery skills.
• Their juvenile performance was accompanied by stronger activation of visual cortices.
• These findings encourage a controlled use of motor imagery for rehabilitation in elderlies.

Motor imagery (M.I.) is a cognitive process in which movements are mentally evoked without overt actions. Behavioral and fMRI studies show a decline of explicit M.I. ability (e.g., the mental rehearsal of finger oppositions) with normal ageing: this decline is accompanied by the recruitment of additional cortical networks.However, none of these studies investigated behavioral and the related fMRI ageing modifications in implicit M.I. tasks, like the hand laterality task (HLT).To address this issue, we performed a behavioral and fMRI study: 27 younger subjects (mean age: 31 years) and 29 older subjects (mean age: 61 years) underwent two event-related design fMRI experiments. In the HLT, participants were asked to decide whether a hand rotated at different angles was a left or right hand. To test the specificity of any age related difference in the HLT, we used a letter rotation task as a control experiment: here subjects had to decide whether rotated letters were presented in a standard or a mirror orientation.We did not find any group difference in either behavioral task; however, we found significant additional neural activation in the elderly group in occipito-temporal regions: these differences were stronger for the HLT rather than for the LRT with group by task interactions effects in right occipital cortices.We interpret these results as evidence of compensatory processes associated with ageing that permit a behavioral performance comparable to that of younger subjects. This process appears to be more marked when the task specifically involves motor representations, even when these are implicitly evoked.