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 subcortic al lesions involving the basal ganglia as well as normal controls were test ed in a language comprehension paradigm. Semantically incorrect, syntactica lly incorrect and correct sentences were presented auditorily, Subjects wer e required to listen to the sentences and to judge whether the sentence hea rd was correct or not. Event-related potentials and reaction times were rec orded while subjects heard the sentences. Three different components correl ated with different language processes were considered: the so-called N400 assumed to reflect processes of semantic integration; the early left anteri or negativity hypothesized to reflect processes of initial syntactic struct ure building; and a late positivity (P600) taken to reflect second-pass pro cesses including re-analysis and repair. Normal participants showed the exp ected N400 component for semantically incorrect sentences and an early ante rior negativity followed by a P600 for syntactically incorrect sentences. P atients with left frontal cortical lesions displayed an attenuated N400 com ponent in the semantic condition. In the syntactic condition only a late po sitivity was observed, Patients with lesions of the basal ganglia, in contr ast, 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 c ortex might support early parsing processes, and that specific regions of t he basal ganglia, in contrast, may not be crucial for early parsing process es during sentence comprehension.