Letter and Category Fluency Performance Correlates with Distinct Patterns of Cortical Thickness in Older Adults

Abstract

Verbal fluency tasks are generally thought to be mediated by frontal brain regions for letter fluency and temporal regions for category fluency. This idea, however, is primarily based on lesion studies and adapted versions of the fluency tasks in functional neuroimaging, without fundamental evidence from structural neuroimaging in healthy individuals. We investigated the cortical structural correlates of letter and category fluency, including overlapping and different regions, in 505 individuals who participated in a community-based study of healthy aging. The correlation between cortical thickness and verbal fluency in whole-brain analyses revealed distinct cortical signatures for letter fluency, primarily in frontal regions, and category fluency, in frontal and temporal-parietal regions. There was a dissociation in the left inferior frontal gyrus between letter and category fluency, with increased thickness in the posterior-dorsal versus anterior-ventral parts, respectively. These results distinguish the detailed anatomical correlates for verbal fluency within the coarse frontal-temporal distinction inferred from lesion studies and among the mixture of regions identified in functional neuroimaging. The evidence for the anatomical substrates of letter and category fluency, each recruiting slightly different language and cognitive processes, can serve both clinical applications as well as a deeper theoretical understanding of the organization of the cerebral cortex.

Semantic loss marks early Alzheimer's disease‐related neurodegeneration in older adults without dementia

“…By controlling for letter fluency when analyzing semantic fluency, and vice versa, the effects of the semantic processing versus executive functioning components can be isolated to a certain extent, 2 to show that these two fluency tasks tap distinctive cognitive processes 41 . Our results display the hybrid character of both tasks in their cortical signature: The ROI analyses confirm previous findings of letter fluency mediating inferior frontal regions and semantic fluency mediating both inferior frontal and temporal‐parietal regions 7,18 . The impairment in semantic fluency in clinical AD is thought to be mediated by neurodegeneration of temporal‐parietal regions 4,19 .…”

C-reactive protein and risk of cognitive decline: The REGARDS study

“…Our results indicate that verbal fluency may be more susceptible to the effects of inflammation than episodic memory. Verbal fluency involves skills related to executive functioning (i.e., updating, inhibition) [37,50] and is associated with integrity of frontal cortical structures, for letter fluency, and frontal and temporal-parietal regions, for semantic fluency [51]. As CRP is considered a marker of vascular disease, these results are in line with research that links vascular risk factors and markers of cerebrovascular disease with impairments in executive functioning [52,53].…”

Longitudinal change in executive function is associated with impaired top-down frontolimbic regulation during reappraisal in older adults

“… 2 Instead of aggregating scores across the verbal fluency-letter and -category task, we opted to include the category part of the verbal fluency task only, because the letter and category raw scores of the last administration of tests were not correlated ( r < .1) , nor were the longitudinal slopes ( r (32) = −.21, p = .23) in our sample. Dissociations between letter and category fluency with respect to involvement of cortical/frontal areas have also been reported elsewhere (for recent findings with a large N see Vonk et al., 2018 ). …”