Engaging the Cortical Action Encoding System in Prosthesis Users by Limb-Matched Movement Imitation
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The mirror neuron system (MNS) has been attributed to increased activation in motor-related cortical areas upon viewing of another's actions. Recent work suggests that limb movements that are similar in appearance to that of the viewer preferentially activate the MNS. It is unclear how this effect applies to amputee prosthesis users. Intact subjects and upper extremity amputees were recruited to view video demonstrations of tools being used by an intact actor and a prosthetic device user. Subjects were asked to pantomime the movement seen in the video while recording electroencephalography. Intact subjects showed equivalent left parietofrontal activity during imitation after watching intact or prosthetic arms. Likewise, when prosthesis users imitated prosthesis demonstrations typical left parietofrontal planning activation was observed. The amputee prosthesis users who imitated intact actors revealed deviations from this pattern, showing greater bilateral parietal and occipital planning and execution activity. We suggest that when prosthesis users imitate intact subjects. the greater bilateral parietal and occipital activation during planning and execution reflects unique visuospatial processing. This change may be required to imitate movements when limb states between the observed and observer do not match. The finding that prosthesis users imitating other prosthesis users showed typical left parietofrontal activation suggests that prosthesis users engage typical planning related activity when they are able to imitate other prosthesis users. This result has significant implications on rehabilitation, as standard therapy involves training with an intact physical therapist, which could necessitate abnormal planning mechanisms in amputees when learning to use their prosthetic device.