INVESTIGATION AND ASSESSMENT OF MIRROR NEURON ACTIVITY FOR REHABILITATION PURPOSES
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Mirror neurons, discovered on prefrontal cortex and subsequently on inferior parietal lobule of macaque monkey, are a class of neurons that become activated with both performing an action and observing the same action. A similar system of neurons also exists in humans. On the basis of features of the putative mirror neuron system (MNS) and its role in action understanding and internal rehearsal (motor imagery) of actions, this action observation-execution matching system has been proposed as a new approach for training in the rehabilitation of patients with motor impairment of the upper limb after stroke. This thesis investigates the mu and/or beta frequency band suppression as an index of the human mirror neuron system (MNS) in Electroencephalography (EEG). Several experimental design and control procedures were applied with the primary objective that the study might be beneficial to motor rehabilitation programs of upper extremities for stroke patients. v In the first experiment, subjects observed different types of objectdirected hand actions in order to explore whether observation of any of these actions may have a relatively strong effect on MNS activity. Here, EEG was recorded at electrode locations C3, C4, P3, P4, F7 and F8. The results showed that all conditions were associated with a significant mu band (8-12 Hz) desynchronization over the somatosensory cortex. Further investigation of the effect of the visual stimuli on MNS revealed the main effect of video stimuli of hand squeezing soft and hard springs, at the frontal channels nearly corresponding to ventral premotor cortex (vPMC) area of the brain. The activation of mirror neurons in this area during action observation plays a crucial role in observational learning. Based on these results, it was proposed that specific type of visual stimuli may be implemented in the action observation-based treatment of stroke patients to have a positive additional impact. Recent evidence suggests that motor imagery might be beneficial to recovery of motor functions after stroke. The implemented strategy in imagery-based rehabilitation may have a crucial role to optimize the imagery performance. In the second experiment, it has been explored if prior execution facilitates the subsequent imagery performance when the motor task to be imagined was associated with a symbolic cue. 10 healthy participants were divided into two groups and performed the execution and imagery of a sequential pinch grip task: one group started the experiment by execution of the task (group named GEF) and the other group performed the imagery session at first stage (group named GIM). Event Related Spectral Perturbations (ERSPs) at mu (8-12 Hz) and beta (15-25 Hz) frequency bands from EEG data were extracted for imagery and execution conditions of 10 subjects over central, parietal and frontal brain regions. The results showed that both simple execution and imagery conditions were associated with a significant (p<0.05) mu and beta band desynchronization over the somatosensory cortex. A significant main effect of frequency was found during imagery condition of 10 subjects and over all relevant channels. This supplies evidence that mu and beta rhythms might have different functional properties for mental rehearsal of actions. ERSP data from two experimentally manipulated groups showed that brain activity (desynchronization) for imagery condition was slightly higher for group GEF. Significant differences between two groups were found at contralateral parietal and bilateral frontal sides. It was concluded that for a cue-based simple motor task, a prior execution of the motor task might facilitate the subsequent imagery task and frontal regions appears to reflect the motor imagery performance. The results will have further implications in imagery-based rehabilitation of patients with stroke. In the last experimental study of this thesis, a fully actuated finger exoskeloton robot ExoPinch was utilized to investigate the anticipatory vi effect of execution on observation. The results showed that the observational condition (with or without anticipation) interacted with hemisphere at central channels near somatosensory cortex. Additionally, the response of MNS was explored on the kinetics features of visual stimuli. The results revealed an interaction effect of kinetics features and hemisphere at frontal channels corresponding nearly to the ventral premotor cortex area of the brain. The activation of mirror neurons in this area plays a crucial role in observational learning. Based on the results, it was proposed that specific type of visual stimuli can be combined with the functional abilities of the MNS in the action observation based treatment of hand motor dysfunction of stroke patients to have positive functional motor responses.