Study separates tool use from physical reasoning after stroke

A familiar tool appeared in a photograph. A participant had to show how it was used; elsewhere in the test, that participant had to predict how objects would interact. At Thomas Jefferson University, researchers found that the two abilities could come apart among 11 patients with left-hemisphere stroke.

The condition is limb apraxia: difficulty using tools despite normal motor control and cognition. It can follow damage to the brain's left hemisphere, affects roughly a quarter of stroke survivors, and is also observed in conditions including Alzheimer's disease. The challenge is not simply a lack of strength or understanding.

The finding unsettles a popular theory that knowing how to use a hammer and understanding how objects physically interact are one skill. One patient without apraxia used tools properly but performed poorly when asked which of two balls was heavier after a collision. Another patient with apraxia showed the opposite pattern. Those profiles appeared in only two patients, but the researchers said they demonstrated that tool use and physical reasoning are independent.

Aaron Wong led the work with researchers at the Jefferson Moss Rehabilitation Research Institute. In ongoing research presented on the bioRxiv preprint server, the team developed tool-free tasks involving balls, ramps and levers, then gave participants separate tasks with unfamiliar tools. Again, some people performed better at one ability than the other. Co-investigator Laurel Buxbaum said tool use may rely partly on mentally simulating body movements, or may be a distinct ability of its own.

Concretely, the potential benefit is for people with limb apraxia who may not have the same underlying difficulty: the results could eventually help researchers design more targeted therapies instead of treating tool use and physical reasoning as one problem. That payoff remains prospective. The Cortex study tested 11 stroke patients, while the related findings are part of ongoing work presented as a bioRxiv preprint, not a treatment.