Giving Meaning to Movement: Evidence for Embodied Semantics from Motor Neurone Disease
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The theory of embodied semantics argues that our ability to understand action words depends on specific areas of the motor system required for performing and simulating the movements that they describe. While this concept has received significant evidence from behavioural and neuropsychological research, the focal onset and insidious spread of motor symptoms in Motor Neurone Disease (MND) provides a unique opportunity to investigate whether the close relationship between movement and language in the brain exists at a somatotopic level. The present multiple case-study investigated working memory performance for nouns compared to verbs in two patients with MND, a group of healthy controls, as well as data from a previously obtained sample of MND patients. Of the 9 cases analysed, 6 patients exhibited a selective verb processing deficit (3 significant, 3 non-significant) for action words associated with the effector most recently affected by motor symptoms. Thus, upper motor neurone (UMN) degeneration in MND appears to affect the ability to access semantic information relating to a particular action concept, prior to having a significant effect on a patient’s ability to perform the movement that a verb describes. Evidence of functional compensation within semantic memory networks involved in verb processing is also presented. While these findings come from a small sample of MND patients, the linked pattern of verb processing and symptom spread observed in over half the cases assessed provides a new base of support for embodied semantics theories, as well as having potential applications in clinical diagnosis and disease monitoring.