Language related brain potentials in patients with cortical and subcortical left hemisphere lesions

The role of the basal ganglia in language processing is currently a matter of discussion. Therefore, patients with left frontal cortical and subcortical lesions involving the basal ganglia as well as normal controls were tested in a language comprehension paradigm. Semantically incorrect, syntactically incorrect and correct sentences were presented auditorily. Subjects were required to listen to the sentences and to judge whether the sentence heard was correct or not. Event-related potentials and reaction times were recorded while subjects heard the sentences. Three different components correlated with different language processes were considered: the so-called N400 assumed to reflect processes of semantic integration; the early left anterior negativity hypothesized to reflect processes of initial syntactic structure building; and a late positivity (P600) taken to reflect second-pass processes including re-analysis and repair. Normal participants showed the expected N400 component for semantically incorrect sentences and an early anterior negativity followed by a P600 for syntactically incorrect sentences. Patients with left frontal cortical lesions displayed an attenuated N400 component in the semantic condition. In the syntactic condition only a late positivity was observed. Patients with lesions of the basal ganglia, in contrast, showed an N400 to semantic violations and an early anterior negativity as well as a P600 to syntactic violations, comparable to normal controls. Under the assumption that the early anterior negativity reflects automatic first-pass parsing processes and the P600 component more controlled second-pass parsing processes, the present results suggest that the left frontal cortex might support early parsing processes, and that specific regions of the basal ganglia, in contrast, may not be crucial for early parsing processes during sentence comprehension.