Deep brain stimulation (DBS) has shown promise in improving motor function in patients with Parkinson’s disease. But little is known about the treatment’s side effects, particularly on language.
Lara Phillips, M.D., David Charles, M.D., professor of Neurology, and colleagues used a language task – the formation of past tense of regular and irregular verbs – to determine how DBS of the subthalamic nucleus (STN-DBS) impacts aspects of language processing. Forming the past tense of irregular verbs (e.g. “dig”) requires memorization of the past tense form (“dug”), whereas conjugation of regular verbs (e.g., “walk”) requires only the application of a simple rule (adding “-ed”) to form the past tense.
The researchers report in PLoS ONE that STN-DBS led to impaired performance with regular verbs (e.g., “walk”), or the “grammatical” aspect of language processing. The procedure did not adversely impact performance with irregular verbs, a measure of “lexical” function.
The results suggest that while DBS may specifically impair grammatical processing, the effect is unlikely to significantly impact patients’ quality of life.
The research was supported by grants from the National Center for Research Resources/National Center for Advancing Translational Sciences (RR024975) and the National Center of Child Health and Human Development (HD049347) of the National Institutes of Health.
