A University of California, San Diego, study shows that the same brain system involved in a sudden stop in physical movement also interrupts cognitive processes. The findings hold implications for Parkinson’s disease, where cognitive impairment is a major symptom.
The study, “Surprise disrupts cognition via a fronto-basal ganglia suppressive mechanism,” focused on a deep brain structure known as the subthalamic nucleus (STN), which is part of the basal ganglia, a group of structures involved in the coordination of movement — and the very structure targeted in deep brain stimulation, a therapeutic technique used in Parkinson’s.
Researchers at UC San Diego have previously shown that this region is active when a sudden interruption of movement is required. In Parkinson’s, an over-activation of the stopping system might cause the slowed-down movement and facial expressions characteristic of the disease. If the new findings are confirmed in future studies, STN will also be shown to contribute to disturbed cognitive processes.
Published in the journal Nature Communications, the study analyzed signals from the STN region in 20 healthy volunteers using scalp electrodes, and in seven Parkinson’s patients with electrode implants in the STN brain region.
All participants received a working memory task, consisting of remembering a string of letters. Before they were asked to recall the letters, a simple, single-frequency tone was played. But in some tests, the tone was replaced by a birdsong — an unexpected event. Researchers noted that this surprise activated the STN in the same way as stopping body movement. The more active the region, the worse the participants performed on the memory test. Recordings from the scalp and deep brain electrodes showed similar results.
“For now, we’ve shown that unexpected, or surprising, events recruit the same brain system we use to actively stop our actions, which, in turn, appears to influence the degree to which such surprising events affect our ongoing trains of thought,” Jan Wessel, the study’s first author and now an assistant professor of psychology and neurology at the University of Iowa, said in a press release.
“An unexpected event appears to clear out what you were thinking,” said Adam Aron, a professor of psychology at UC San Diego. “The radically new idea is that just as the brain’s stopping mechanism is involved in stopping what we’re doing with our bodies, it might also be responsible for interrupting and flushing out our thoughts.”