Action-verb processing in Parkinson’s disease: new pathways for motor–language coupling

Abstract

Recent studies suggest that action-verb processing is particularly affected in early stage Parkinson's disease (PD), highlighting the potential role of subcortical areas in language processing and in the semantic integration of actions. However, this disorder-related language impairment is frequently unrecognized by clinicians and often remains untreated. Early detection of action-language processing deficits could be critical for diagnosing and developing treatment strategies for PD. In this article, we review how action-verb processing is affected in PD and propose a model in which multiple and parallel frontotemporal circuits between the cortex and the basal ganglia provide the anatomic substrate for supporting action-language processing. We hypothesize that contextual coupling of action-language networks are partially dependent on cortical-subcortical integration, and not only on somatotopic motor cortical organization or in a mirror neuron system. This hypothesis is supported by both experimental and clinical evidence. Then, we identify further research steps that would help to determine the reliability of action-language impairments as an early marker of PD. Finally, theoretical implications for clinical assessment and for models of action-language interaction (action-perception cycle theories, mirror system models of language, and embodied cognition approaches to language) are discussed.

Words in motion: Motor-language coupling in Parkinson’s disease

“…Unlike the other Indo-European languages considered, Chinese lacks explicit word-class contrasts in its grammatical morphology, which suggests that neural noun-verb dissociations may be influenced by structural properties of the individual's native language. [57,58] (for further discussion of the model, see [48,59] [13,15], amyotrophic lateral sclerosis [14,60], corticobasal degeneration [61,62], and frontotemporal dementia [63,64]. This evidence A classic ACE (compatible facilitation and incompatible delay of RTs) was observed for controls, but no ACE was observed in early PD participants.…”

“…The temporal lobe, the basal ganglia, and the thalamus (temporal-basal ganglia-thalamocortical component) comprise loops that would play a central role in the grounding of abstract conceptual knowledge involved in words referring to motor concepts. Modified with permission from [59].…”

Syntax, action verbs, action semantics, and object semantics in Parkinson's disease: Dissociability, progression, and executive influences

“…For example, Cardona et al (2013) and Ibáñez et al (2013) postulate that action-verb processing and motor-language coupling depend on a network involving loops from cortical areas to BG/thalamic structures and back to the cortex. Hence, BG affectation in early PD would lead to the selective disruption of this language domain.…”

Neural Foundations of Action-related Language: Studies in Parkinson’s Disease

“…The motor theory of language based on the Embodied Cognitive Theory suggests that action-related language is located in the areas of the brain related with action. Indeed, the activation of the primary motor and premotor cortex while processing words or sentences that describe action including movement of the mouth, hand or leg supports this theory (4). In contrast, there are also studies showing that activation of cortical motor areas that have somatotopic organization with action-related language does not follow somatotopic organization (6).…”

“…These disturbances include morphosyntactic, lexicalsemantic, and discourse-level processes. Studies show disturbances in language functions including understanding long and complex sentences, action word recognition, action word naming and producing, and metaphor comprehension (4). Although some of these disturbances are associated with impairment in cognitive processes including executive functions, working memory, and selective attention, some studies showed that language disturbances were independent from cognitive decline (4).…”