Language Comprehension in Parkinson’s Disease: The Case of Temporal Connectives

Abstract

Language dysfunction is not normally considered to be a typical symptom of Parkinson’s disease (PD). Previous studies, however, have shown that PD might lead to comprehension deficits whenever a language task taxes verbal working memory. A case in point are sentences starting with temporal connectives (before or after). While “After A, B” sentences state the events in the same order as they occurred in real life, the event-order is reversed in “Before B, A”. Neuroimaging studies have revealed that the caudate nucleus is important for the additional computations necessitated by the processing of ‘before’-initial sentences, suggesting that such sentences should be particularly difficult for patients suffering from basal ganglia diseases such as PD. In the present investigation, we compared a group of PD patients with normal control participants. A further group of patients with restless legs syndrome (RLS) treated with dopaminergic medication was also tested. Replicating earlier studies, PD patients were disproportionately impaired in comprehending ‘before’-initial sentences. Importantly, this deficit was also observed in unmedicated de novo patients, suggesting that these difficulties occur relatively early in the disease. RLS patients also had increased error rates compared to healthy controls. This latter finding should be confirmed in further studies.