The effects of subthalamic nucleus stimulation on semantic and syntactic performance in spontaneous language production in people with Parkinson's disease

•Semantic and syntactic features of spontaneous speech in PD are disrupted.•Stimulation of only the left STN affects linguistics parameters negatively.•Multiple factors influence the effect of stimulation on spontaneous speech.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has become an established therapeutic option for advanced Parkinson's disease (PD). In this study, the effects of unilateral and bilateral STN stimulation on spontaneous language production are explored, by comparing linguistic performance in different stimulation conditions with normative data of healthy subjects.Language samples of ten PD patients with DBS of the STN were obtained in four stimulation conditions: bilateral stimulation on, bilateral stimulation off, stimulation of the left STN only and stimulation of the right STN only. The spontaneous language production differed from the normative data in all four stimulation conditions. Especially morphosyntactic elements of spontaneous language production were altered. Despite these linguistic differences with normal controls no significant differences between stimulation conditions were found. These results emphasize that the effects of STN stimulation on spontaneous language production reflect a complex interplay of multiple factors.