Reaching for domain-general syntax: Sentence processing and tool-use reach-to-grasp share neural patterns in the basal ganglia

Are actions organized like sentences? Recent evidence showed reciprocal transfer between tool use and syntactic comprehension, reflecting shared basal ganglia resources for action and language. The proposed mechanism is that embedding a tool into the motor plan increases the hierarchical structure of actions, paralleling the organization of sentences. If so, overlap with linguistic computations should emerge specifically during the initiation and/or reach-to-grasp phase, when tool embedding dynamically updates the relation with the target, rather than when the object is stably held in the tool grip. Forty French native speakers completed a sentence comprehension task involving object- and subject-relative clauses, and a motor task consisting of grasping and manipulating an object either with a tool or with the bare hand. Using both univariate and multivariate analyses, we found that the comprehension of syntactically complex sentences and the reach-to-grasp phase of tool use elicited overlapping and similar neural codes within the basal ganglia. This phase-specific convergence identifies the basal ganglia as a hub for domain-general hierarchical computations, unifying syntactic embedding for language and tool use.