Partly segregated cortico-subcortical pathways support phonologic and semantic verbal fluency: A lesion study

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neurolinguistics

Background:

• Verbal fluency tasks assess word generation under phonologic or semantic constraints.
• Existing research implicates left fronto-temporal regions, but distinct neural substrates for phonologic versus semantic fluency are debated.

Purpose of the Study:

• To investigate the hypothesis of segregated cortico-subcortical structures underlying phonologic and semantic verbal fluency.
• To identify specific brain regions whose damage affects verbal fluency performance.

Main Methods:

• Voxel-based lesion symptom mapping (VLSM) was employed.
• 191 patients with unilateral brain lesions were assessed for phonologic and semantic fluency, controlling for age and education.

Main Results:

• A positive correlation between phonologic and semantic fluency scores suggests shared underlying mechanisms.
• Lesions to the left basal ganglia universally impaired both fluency types.
• Left superior temporal, supramarginal, and rolandic operculum lesions selectively impaired phonologic fluency.
• Left middle temporal lesions selectively impaired semantic fluency.

Conclusions:

• The basal ganglia play a common executive role in word generation, irrespective of fluency type.
• Distinct cortical regions, specifically ventral and dorsal language pathways, are preferentially involved in semantic and phonologic fluency, respectively.
• Findings refine neurocognitive models of word retrieval and lexical search.