Neural systems supporting lexical search guided by letter and semantic category cues: A self-paced overt response fMRI study of verbal fluency

Abstract

Verbal fluency tasks have been widely used to evaluate language and executive control processes in the human brain. FMRI studies of verbal fluency, however, have used either silent word generation (which provides no behavioral measure) or cued generation of single words in order to contend with speech-related motion artifacts. In this study, we use a recently developed paradigm design to investigate the neural correlates of verbal fluency during overt, free recall, word generation so that performance and brain activity could be evaluated under conditions that more closely mirror standard behavioral test demands. We investigated verbal fluency to both letter and category cues in order to evaluate differential involvement of specific frontal and temporal lobe sites as a function of retrieval cue type, as suggested by previous neuropsychological and neuroimaging investigations. In addition, we incorporated both a task switching manipulation and an automatic speech condition in order to modulate the demand placed on executive functions. We found greater activation in the left hemisphere during category and letter fluency tasks, and greater right hemisphere activation during automatic speech. We also found that letter and category fluency tasks were associated with differential involvement of specific regions of the frontal and temporal lobes. These findings provide converging evidence that letter and category fluency performance is dependent on partially distinct neural circuitry. They also provide strong evidence that verbal fluency can be successfully evaluated in the MR environment using overt, self-paced, responses.

Methodological Criteria for Scoring Clustering and Switching in Verbal Fluency Tasks

“…Studies of patients with brain lesions have suggested that impaired performances on PVF tasks are related to frontal lobe lesions, particularly in the left hemisphere (Birn et al, 2010;Troyer, Moscovitch, Winocur, Alexander, & Stuss, 1998;Troyer, Moscovitch, Winocur, Leach, & Freedman, 1998). In contrast, SVF tasks require the use of a smaller number of sets of words, because these tasks recruit words within a particular semantic category (Troyer et al, 1997).…”

“…In contrast, SVF tasks require the use of a smaller number of sets of words, because these tasks recruit words within a particular semantic category (Troyer et al, 1997). In this case, studies using the lesion paradigm have shown impaired performances on these tasks associated with lesions in the temporal lobes (Birn et al, 2010;Troyer, Moscovitch, Winocur, Alexander et al, 1998;Troyer, Moscovitch, Winocur, Leach et al, 1998).…”

Are subjective cognitive complaints related to memory functioning in the working population?

“…The second task was to produce professions beginning with the letter B (Nilsson et al 2004;Nilsson et al 1997). While fluency tests tap semantic memory functioning, it should be pointed out that (especially letter-) fluency tasks also rely on executive processes and associated prefrontal cortical brain regions (e.g., Birn et al 2010). This has been most evident in patients with severe/manifest prefrontal brain damage becoming severely impaired on fluency tasks.…”

Language, executive functioning and symptomatology—Is fluency a transversal tool in schizophrenia?

“…Although we may think that fluency disorders are linked with a general linguistic problem, they equally seem to be part of a broader executive problematic. Verbal fluency is indeed fundamentally different from spontaneous and automatic speech [13] and requires various processes going from the lexical selection and the phonemic encoding to working memory and cognitive control abilities ( [1,14]). …”