Action/Verb processing: Debates in neuroimaging and the contribution of studies in patients with Parkinson's disease

Abstract

The objective of the current review was to verify whether studies investigating lexical-semantic difficulties in patients with Parkinson's disease (PD) support the Embodied Cognition model. Under this framework, it is predicted that patients with PD will have more difficulties in the semantic processing of action concepts (action verbs) than of motionless objects. We also verified how and whether these studies are following current debates of Neuroscience, particularly the debate between the Lexical and the Embodied Cognition models. Recent neuroimaging studies on the neural basis of the semantics of verbs were presented, as well as others that focused on the neural processing of verbs in PD. We concluded that few studies suitably verified the Embodied Cognition theory in the context of PD, especially using neuroimaging techniques. These limitations show there is much to investigate on the semantic difficulties with action verbs in these patients, where it is particularly important to control for psycholinguistic variables and the inherent semantic characteristics of verbs in future studies.

Are the motor features of verb meanings represented in the precentral motor cortices? Yes, but within the context of a flexible, multilevel architecture for conceptual knowledge

“…Furthermore, in the lesion study by Kemmerer et al (2012) described above, it is possible that the patients who failed the tasks did so not because of their tendency to have damage in left precentral arm/hand-related motor areas, but rather because of their tendency to have damage in one or more of several other left-hemisphere regions that have been associated with action concepts-specifically, the inferior frontal gyrus, the supramarginal gyrus, and the posterior middle temporal gyrus (see also Urgesi et al, 2014). In addition, even though there is, as indicated above, some evidence that Parkinson's disease disrupts the comprehension of action verbs, the impairments in these patients are often mild and may affect non-action verbs as well (Kemmerer et al, 2013; see also Da Silva, Machado, Cravo, Parente, & Carthery-Goulart, 2014).…”

Are Action Concept Deficits Embodied in a Topographic Manner in Adults with Cerebral Palsy?

“…What does this lack of clear differences between groups suggest? One possibility is that CP only mildly disrupts motor simulations during verb comprehension, thus CP participants were still able to determine the semantic relations among the action verbs in the identity-priming paradigm (Kemmerer et al, 2013;Silva, Machado, Cravo, Parente, & Carthery-Goulart, 2016). This view is still compatible with the strong form of the embodied cognition framework and predicts that CP participants would exhibit lower accuracies on a task that required substantially more attention to the motor and effector features of verb meanings.…”

“…In the present study, no other regions involved in action verb processing semantics, including the inferior frontal gyrus which is known to be particularly relevant (Urgesi, Candidi, & Avenanti, 2014), were analyzed, which may explain our lack of EEG results between groups. These results allow that motor representations may enrich the concepts of verbs but the simulations are not necessary for the comprehension of verbs (Kemmerer et al, 2013;Silva et al, 2016). In adopting the weak view of the theory, I also leave room for the effects of psycholinguistic factors known to affect language performance such as frequency of word use and social network size (Kuperman et al, 2012;Lev-Ari, 2016;Silva et al, 2016).…”

“…If the integrity of the motor system is necessary for action semantics, a clear impairment must be demonstrated in CP. However, if the motor system contributes to, but is not necessary for, action verb processing, then patients may present no clear deficits compared to controls (Silva et al, 2016), or they may exhibit time but not accuracy differences as shown in the completed work. A similar pattern of results was found in stroke patients, who despite having lesions involving some pre-central motor areas, showed no significant correlations between impaired performance on body-part-specific action categories and damage to the corresponding body-part-specific motor areas (Arévalo, Baldo, & Dronkers, 2012;Kemmerer et al, 2013).…”

“…This accessory view would not refute the embodied cognition claim, but would challenge the strong form of this theory. A weak theory however, maintains that it is not always necessary to run motor simulations in left frontal regions in order to appreciate the nuances of action verbs (Silva et al, 2016); instead, other types of modality-specific semantic representations subserved by other cortical areas may be adequate for many comprehension tasks, as has already been shown in fMRI paradigms for a variety of action verbs (Kemmerer, Castillo, Talavage, Patterson, & Wiley, 2008). Thus, patient populations with so called disability-specific action verb semantic deficits may have such issues not because only their M1 regions relating to arm or leg regions are damaged but rather because of their tendency to have damage/ an underdevelopment in one or more of several other left-hemisphere regions that have been associated with action concepts-specifically, the inferior frontal gyrus, the supramarginal gyrus, and the posterior middle temporal gyrus which have been shown to be reactive in athletes as well (Kemmerer, 2015;Milton et al, 2007).…”