Differential role of prefrontal, temporal and parietal cortices in verbal and figural fluency: Implications for the supramodal contribution of executive functions

Elham Ghanavati,Mohammad Ali Salehinejad,Michael A Nitsche,Vahid Nejati

doi:10.1038/s41598-019-40273-7

Abstract

Verbal and figural fluency are related to executive functions (EFs), but the extent to which they benefit from executive resources and their respective cortical representations is not clear. Moreover, different brain areas and cognitive functions are involved in fluency processing. This study investigated effects of modulation of cortical excitability in the left dorsolateral prefrontal cortex (l-DLPFC), left temporal area and right posterior parietal cortex (r-PPC) with transcranial direct current stimulation (tDCS), on verbal and figural fluency. Fifteen healthy adult participants received anodal l-DLPFC (F3), anodal left temporal (T3), anodal r-PPC (P4) and sham tDCS (15 min, 1.5 mA). After five minutes of stimulation, participants underwent the verbal fluency (i.e., semantic and phonemic fluency tasks) and figural fluency tasks. Participants significantly generated more words with phonemic cues during anodal l-DLPFC tDCS and more words with semantic cues during both anodal left temporal and anodal l-DLPFC tDCS. In contrast, they generated more unique figures under anodal r-PPC and anodal l-DLPFC tDCS. Our results implicate that prefrontal regions and EFs are shared anatomical correlates and cognitive processes relevant for both, verbal and figural fluency (supramodal contribution of DLPFC activation), whereas r-PPC and left temporal cortex are more specifically involved in figural and semantic fluency (modality-specific contribution).

Highlights

Verbal and figural fluency are related to executive functions (EFs), but the extent to which they benefit from executive resources and their respective cortical representations is not clear
These findings suggest that the dorsolateral prefrontal cortex (DLPFC) might have a supramodal contribution to fluency similar to its well-documented role in EFs28, whereas other brain areas including the medial prefrontal cortex (mPFC) and medial temporal region contribute to specific verbal fluency functions
The data overview shows that performance of verbal fluency and Five Point Test (FPT) tasks differed between transcranial direct current stimulation (tDCS) conditions (Fig. 3)

Summary

Introduction

Verbal and figural fluency are related to executive functions (EFs), but the extent to which they benefit from executive resources and their respective cortical representations is not clear. Converging evidence from clinical populations confirm reduced activity in the left dorsolateral prefrontal cortex (DLPFC) related to impaired verbal fluency ability independent of modality[22,23,24] When it comes to fluency within specific modalities (i.e., semantic fluency, phonemic fluency, figural fluency), other cognitive processes and their associated brain areas are involved. Neuroimaging studies found greater activation in the left hemisphere during semantic and phonemic fluency tasks especially in the anterior cingulate and left prefrontal regions[19], whereas the medial prefrontal cortex (mPFC) and medial temporal regions are relevant for semantic fluency[5,27] These findings suggest that the DLPFC might have a supramodal contribution to fluency similar to its well-documented role in EFs28, whereas other brain areas including the mPFC and medial temporal region contribute to specific verbal fluency functions. Imaging findings show that the PFC and PPC interact in achieving cognitive control in a way that neural activity in the prefrontal areas precedes parietal activity[35]

Methods

Results

Conclusion