12:02am Tuesday 14 July 2020

New brain imaging study advances understanding of how humans use tools

Jody Culham from Western’s Brain and Mind Institute and Jason Gallivan, who received a PhD in Neuroscience from Western and is now at the Centre for Neuroscience Studies (CNS) at Queen’s, were especially interested in determining whether human brain regions involved in planning actions with the hand alone would also be involved in planning actions with a tool.

The findings, published in the new science journal eLife, show that while in some brain regions this is true; in other regions, the brain appears to only be selectively involved in planning actions of the hand alone or the tool alone. Interestingly, the tool-specific brain areas were found in some of the zones of cerebral cortex that have shown the greatest expansion with evolution, suggesting a possible neural origin for humans’ highly sophisticated ability to use tools.

“Tool use represents a defining characteristic of high-level cognition and behaviour across the animal kingdom but studying how the brain – and the human brain in particular – supports tool use remains a challenge for neuroscientists. This work is a considerable step forward in our understanding of how tool-related actions are planned in humans,” explains Gallivan, who served as first author of the paper titled, “Decoding the neural mechanisms of human tool use.”

Over the course of the one-year study, human participants had their brain activity scanned using functional magnetic resonance imaging (fMRI) as they reached towards and grasped objects using either their hand or a set of plastic tongs. Importantly, the tongs had been designed so that they opened whenever the participants closed their grip, requiring that the participants perform a different set of movements to use the tongs as opposed to when their hand was used alone.

The researchers discovered that seconds before the action began, the neural activity in some brain regions only predicted the type of action to be performed upon the object, regardless of whether the hand or tool was to be used (and despite the different movements being required). However, other brain regions represented hand and tool actions separately. Specifically, some brain regions only predicted actions with the hand whereas others only signaled actions with the tool.

“One of the most popular modern accounts of how the brain supports tool use suggests that tools, through experience, may become embodied. The idea is that the brain mechanisms devoted to bodily actions, and hand actions in particular, may come to incorporate tools into their neural codes,” explains Culham, the paper’s senior author. “Our findings show that although some brain areas may in fact represent a tool as an extension of the hand, not all brain areas do so. In the human, distinct brain areas may have evolved to enable more complex tool use.”

The work was funded by the Canadian Institutes of Health Research (CIHR). A past recipient of three CIHR Brain Star Awards, Gallivan is currently funded by a Banting Postdoctoral Fellowship.

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