Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Gribble, Paul L.


An influential idea in neuroscience is that action observation activates an observer’s sensory-motor system. This idea has recently been extended to motor learning; observing another individual undergoing motor learning can promote sensory-motor plasticity as well as behavioural changes in both the motor and somatosensory domains. While previous research has suggested a role for the motor system in motor learning by observing, this thesis presents a series of experiments testing the hypothesis that the somatosensory system is also involved in motor learning by observing.

The experiments included in this thesis used force field (FF) adaptation as a model of motor learning, a task in which subjects adapt their reaches to a robot-imposed FF. Subjects observed a video showing another individual adapting his or her reaches to a FF, and motor learning by observing was assessed behaviourally following observation.

First, we used functional magnetic resonance imaging (fMRI) to assess changes in resting-state functional connectivity (FC) associated with motor learning by observing. We identified a functional network consisting of visual area V5/MT, cerebellum, primary motor cortex (M1), and primary somatosensory cortex (S1) in which post- observation FC changes were correlated with subsequent behavioural measures of motor learning achieved through observation.

We then investigated if pre-observation measures of brain function or structure could predict subsequent motor learning by observing. We found that individual differences in pre-observation resting-state FC predicted observation-related gains in motor learning. Subjects who exhibited greater FC between bilateral S1, M1, dorsal premotor cortex (PMd), and left superior parietal lobule (SPL) prior to observation achieved greater motor learning by observing on the following day.

In a subsequent experiment, we tested the involvement of the somatosensory system in motor learning by observing using median nerve stimulation and electroencephalogra- phy (EEG). In experiment 1, we showed that interfering with somatosensory cortical processing throughout observation (by delivering median nerve stimulation) can disrupt motor learning by observing. In a follow-up experiment, we assessed pre- to post- observation changes in S1 excitability by acquiring somatosensory evoked potentials

(SEPs) using EEG. We showed that SEP amplitudes increased after observing motor learning. Post-observtion SEP increases were correlated with subsequent behavioural measures of motor learning achieved through observation.

In a final experiment, we tested if improving subjects’ somatosensory function would enhance subsequent motor learning by observing. Subjects underwent perceptual training to improve their proprioceptive acuity prior to observation. We found that improving proprioceptive acuity prior to observation enhanced the extent to which subjects benefitted from observing motor learning (compared to subjects who had not undergone perceptual training). We further found that post-training increases in proprioceptive acuity were correlated with subsequent observation-related gains in motor performance.

Collectively, these studies suggest that motor learning by observing is supported by a fronto-parieto-occipital network in which the somatosensory system is an active element. We have shown that observing motor learning changes somatosensory activity in a behaviourally-relevant manner. Observing motor learning resulted in S1 plasticity that corresponded to the extent of learning achieved through observation. Moreover, manipulating somatosensory activity influenced motor learning by observing. Interfering with somatosensory processing throughout observation disrupted motor learning by observing whereas improving somatosensory function prior to observation enhanced motor learning by observing. These experiments therefore suggest that the somatosensory system is indeed involved in motor learning by observing.