Learning of Action and Perception in Walking

Motor adaptation is a trial and error process that allows us to adjust our movements in response to changes in our environment and our body. It is thought that this process recalibrates a forward model (potentially housed in the cerebellum), which predicts the sensory consequences of our motor actions. This has been typically thought to be a recalibration of the motor system. However, recent evidence in reaching adaptation studies has shown that there are also changes to sensory perception, specifically kinesthesia, that accompany motor changes. This dissertation examines which sensory perceptual changes occur during walking adaptation, the role of the cerebellum in these changes and how we can modulate them by changing the way individuals learn. First, we studied changes in lower limb speed, position and force perception after subjects learned a new locomotor pattern on a split-belt treadmill. For each psychophysical experiment, we compared groups of healthy individuals who either learned a new pattern (experienced a 3:1 split-belt perturbation) or did not (walked at a tied fast speed). We found that of these three parameters, walking speed perception was the only one that changed significantly after learning a new walking pattern. We then went on to test whether this change to speed perception was a general one by testing generalization to a backwards walking direction. As expected, we found there was no transfer to the backwards direction in either the motor or speed perception domains. This suggests that the perceptual change may be specific to the context of walking and stem from the discrepancy between expected and actual leg motions following split-belt adaptation. In our second study, we used the previous protocol for testing changes in speed perception in individuals with cerebellar ataxia. We compared this to healthy age-matched subjects. Surprisingly, we found that patients had preserved temporal components of motor adaptation, compared to healthy controls. We also found that in addition to spatial motor deficits, which we have previously shown, ataxia patients also showed aftereffect deficits in walking speed perception. These results implicate the involvement of the cerebellum in the recalibration of both motor and walking speed perception during split belt adaptation. In our final study, we studied how we could modulate motor and speed perception aftereffects by changing the way subjects learned on the split-belt treadmill. We carried this out by applying different perturbations (abrupt versus gradual) to separate groups of healthy individuals. Surprisingly, we found that despite the fact that groups learned the same amount in the motor domain, the group that learned from a gradual perturbation showed much larger aftereffects in speed perception. This suggests involvement of another mechanism, perhaps one that deals with the explicit nature of errors, which can differentially affect the recalibration of sensory perception associated with learning a new walking pattern. Taken together, these results suggest that walking speed is a salient perception that changes with split-belt adaptation, that it is affected by damage to the cerebellum and it can be changed depending on the size of errors experienced during learning