Abstract
Action-perception circuits containing neurons in the motor system have been proposed as the building blocks of higher cognition; accordingly, motor dysfunction should entail cognitive deficits. Autism spectrum conditions (ASC) are marked by motor impairments but the implications of such motor dysfunction for higher cognition remain unclear. We here used word reading and semantic judgment tasks to investigate action-related motor cognition and its corresponding fMRI brain activation in high-functioning adults with ASC. These participants exhibited hypoactivity of motor cortex in language processing relative to typically developing controls. Crucially, we also found a deficit in semantic processing of action-related words, which, intriguingly, significantly correlated with this underactivation of motor cortex to these items. Furthermore, the word-induced hypoactivity in the motor system also predicted the severity of ASC as expressed by the number of autistic symptoms measured by the Autism-Spectrum Quotient (Baron-Cohen etal., 2001). These significant correlations between word-induced activation of the motor system and a newly discovered semantic deficit in a condition known to be characterized by motor impairments, along with the correlation of such activation with general autistic traits, confirm critical predictions of causal theories linking cognitive and semantic deficits in ASC, in part, to dysfunctional action-perception circuits and resultant reduction of motor system activation.
Highlights
A surprising finding in contemporary neuroscience concerns the motor system’s function as a vehicle for higher cognitive processes which, on first glance, appear to be entirely unrelated to basic motor function
FMRI RESULTS: FRONTAL-MOTOR HYPOACTIVITY IN Autism spectrum conditions (ASC) In both groups (18 ASC vs. 18 typically developing (TD) participants), the contrast of all words against baseline [strings of repeated familiar symbols] revealed similar activation patterns in posterior temporal regions, which are typically activated by written word stimuli (Cohen et al, 2002)
Following stringent www.frontiersin.org whole-brain correction for multiple comparisons (p < 0.05, FWE corrected), direct statistical comparison of word-elicited activations between both groups still confirmed that ASC subjects showed reduced inferior-frontal and precentral activation compared with TD controls (Figure 2B)
Summary
A surprising finding in contemporary neuroscience concerns the motor system’s function as a vehicle for higher cognitive processes which, on first glance, appear to be entirely unrelated to basic motor function. The sensorimotor patterns for hearing and articulating a word (represented in core perisylvian language areas, Figure 1A) become linked to the differential areas activated by experiencing/interacting with actions or objects, forming conceptual circuits for words. Action words such as “grasp,” which semantically relate to the concepts of actions represented by action schemas stored in cortical motor systems, draw upon motor systems, whilst object words relate to visual objects and are processed in the temporo-occipital visual processing stream.
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