Human neuroimaging reveals differences in activation and connectivity between real and pantomimed tool use

Abstract

Because the sophistication of tool use is vastly enhanced in humans compared to other species, a rich understanding of its neural substrates requires neuroscientific experiments in humans. Although functional magnetic resonance imaging (fMRI) has enabled many studies of tool-related neural processing, surprisingly few studies have examined real tool use. Rather, due to the many constraints of fMRI, past research has typically used proxies such as pantomiming despite neuropsychological dissociations between pantomimed and real tool use. We compared univariate activation levels, multivariate activation patterns, and functional connectivity when participants used real tools (a plastic knife or fork) to act upon a target object (scoring or poking a piece of putty) or pantomimed the same actions with similar movements and timing. During the Execute phase, we found higher activation for real vs. pantomimed tool use in sensorimotor regions and the anterior supramarginal gyrus, and higher activation for pantomimed than real tool use in classic tool-selective areas. Although no regions showed significant differences in activation magnitude during the Plan phase, activation patterns differed between real vs. pantomimed tool use and motor cortex showed differential functional connectivity. These results reflect important differences between real tool use, a closed-loop function process constrained by real consequences, and pantomimed tool use, a symbolic gesture that requires conceptual knowledge of tools but with limited consequences. These results highlight the feasibility and added value of employing natural tool use tasks in functional imaging, inform neuropsychological dissociations, and advance our theoretical understanding of the neural substrates of natural tool use.

Significance Statement

The study of tool use offers unique insights into how the human brain, synthesizes perceptual, cognitive, and sensorimotor functions to accomplish a goal. We suggest that the reliance on proxies, such as pantomiming, for real tool use, has (1) overestimated the contribution of cognitive networks because of the indirect, symbolic nature of pantomiming; and (2) underestimated the contribution of sensorimotor networks necessary for predicting and monitoring the consequences of real interactions between hand, tool, and the target object. These results enhance our theoretical understanding of the full range of human tool functions and inform our understanding of neuropsychological dissociations between real and pantomimed tool use.