August 31, 2015 | Erin Bluvas, bluvase@sc.edu
A team of researchers from the Department of Psychology and the Arnold School of Public Health at the University of South Carolina have discovered that our ability to understand the meanings of words is at least partly based in the motor and sensory systems of the brain (e.g., motor cortex, visual cortex). The study, published in Neuropsychologia, sheds light on the controversial and complicated relationship between the brain’s conceptual and sensory-motor systems.
“Traditionally, people think of concepts or meanings in the brain as separate from sensory and motor systems of the brain because we can talk about ‘throwing’ without actually throwing something” says Rutvik Desai, an associate professor of psychology and lead author on the study. “However, our research has shown that the meanings of action words like 'throw' are stored in the brain in a way that uses motor cortical areas of the brain,” he explains. “In other words, to understand the word 'throw,' you use the part of the brain that you use to do actual throwing.”
The research took place in Assistant Professor Troy Herter’s state of the art Sensory Motor And Robotic Technology (SMART) lab. A part of the Blanchard Machinery Company Rehabilitation Laboratory, this lab uses robotic technology to measure arm movements that allow the researchers to probe sensory, motor and cognitive function. “Our lab was ideally suited for this research because our robotic apparatus allows us to quantify motor function using continuous measures that are highly sensitive to varying degrees of impairment,” says Herter, who is the Head of the Rehabilitation Sciences Division within the Arnold School’s Department of Exercise Science.
The researchers tested the motor abilities of stroke patients using a robotic device that generated precise measurements of their physical movements. The team also tested the patients’ ability to understand action words, such as “reach” and “pinch.” They found that the more impaired a patient was in his/her movements, the more impairment s/he had in understanding action words. “This shows that meanings or concepts in the brain are at least partly based on motor systems of the brain, so that if you damage action performance, you also damage action meaning,” says Desai. “Another way to say it is that the 'thinking' and 'doing' systems of the brain are not separated, but linked.”
The implications of these findings suggest that recovery of speech-language function may require treatment aimed at both speech-language function and motor function. “Clinically, I believe this work shows how deficits in one neurological domain can affect other domains, thus rehabilitation specialists will need to consider how recovery of one function may not occur without recovery of other functions,” Herter says.
In terms of next steps, the team will continue to investigate how sensory, motor and cognitive impairments influence speech-language function. This will include studies aimed at uncovering both the behavioral interactions and the neurological mechanisms that underlie these interactions.
Additional co-authors on the study include Nicholas Riccardi (Psychology), Christopher Rorden (Psychology) and Julius Fridriksson (Communication Sciences and Disorders).