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Action domains; Activation Likelihood Estimation; Meta-Analytic Connectivity Modelling; Broca’s area
Abstract:
Actions can be described in terms of modality of domain (e.g., imitation) and features of the movement (e.g., presence/absence of objects, complex/simple motor outputs). At the neuroanatomical level, conclusive evidence for both modality-specific phenomena and feature processing across multiple action domains remains sparse. Here we ask: (1) What neural resources are required to process actions within specific modalities? (2) Are the same motor features coded through similar neural networks in different modalities? By using quantitative Activation Likelihood Estimation (ALE) and Meta-Analytic Connectivity Modelling (MACM) methods, we obtained cumulative activity distributions of 416 previously published neuroimaging experiments to disentangle functional specificities of six action domains: (1) execution, (2) imitation, (3) observation, (4) imagery, (5) learning, and (6) planning. Our results show distinct functional patterns for the different domains, with cross-modal convergence for execution, imitation and imagery in the posterior Brodmann Area (pBA) 44 of the left inferior frontal gyrus (IFG). Fine-grained analyses in pBA44 reveals that activity in the region does not correlate with movement complexity, but rather with non-object-directed actions. Furthermore, the functional connectivity network seeding in the motor-based localized cluster of pBA44 differs from the connectivity network seeding in the (language-related) anterior BA44. Bringing the results together, we propose that the motor-related network encompassing pBA44 is recruited when processing simple movements, especially when the focus is on finger positioning. This, we believe, questions the role of the left IFG as a domain-general hub for processing syntactic complexity and simultaneously fails to support a mirror neuron hypothesis of action processing.
