Penn and Drexel Research Team Use Noninvasive Brain Stimulation to Study Language
By Emily Schalk
Danielle Bassett, Eduardo D. Glandt Faculty Fellow, recently collaborated on a study that explores how the brain completes open-ended and close-ended language tasks. She worked with colleagues at Drexel University, including former lab member John Medaglia, and at Penn, including Roy Hamilton, associate professor and director of Perelman School of Medicine’s Laboratory for Cognition and Neural Stimulation, and Denise Harvey, a postdoctoral researcher in his lab.
Bassett, an associate professor in the Departments of Bioengineering and Electrical and Systems Engineering, has previously investigated language networks in patients with temporal lobe epilepsy, and has collaborated with Medaglia before for a study on cognitive flexibility.
This new study, published in The Journal of Neuroscience, focuses on the left inferior frontal gyrus, a region of the brain responsible for language production and word processing, as a target for a form of noninvasive neurostimulation called transcranial magnetic stimulation, or TMS.
“Network neuroscience provides computational methods to uncover structure in brain imaging data. In turn, knowledge about this structure allows us to better understand how signals travel naturally across the brain’s highways, and also how stimulation can alter that travel in a way that supports better cognitive function,” said Bassett in Drexel’s coverage of the study.
Twenty-eight study subjects were asked to complete two different kinds of language tasks while the research team administered the noninvasive brain stimulation. In the first type of task, study participants completed open-ended sentences such as, “They left the dirty dishes in the…” and were instructed to say a single word that would appropriately complete it. In the second type of task, study participants were asked to name specific images or numerals presented to them.
For each task, the researchers measured the participants’ response times and administered brain stimulation. After collecting the data, the researchers used mathematical formulas to study the controllability of the brain’s network systems. They were focused on how the language tasks affected two distinct network control features: modal controllability, which is the ability of a brain region to drive a network into “difficult to reach” states and boundary controllability, the theoretical ability of a brain region to guide distinct brain networks to communicate with each other.
The researchers found that boundary controllability represented a process important for responding in the open-ended language tasks, when participants needed to retrieve and select a single word in the face of competing, alternative responses. By contrast, modal controllability was closely related to closed-ended language tasks. This suggests that the LIFG’s ability to integrate and segregate communication between brain networks may not play an important role when people are selecting a single, correct word, rather than choosing among several possibilities.
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