Functional Connectivity during Phonemic and Semantic Verbal Fluency Test: A Multichannel Near Infrared Spectroscopy Study

Verbal fluency tests (VFTs) are widely used frontal lobe neuropsychological tests. They have been frequently used in various functional brain mapping studies. There are two versions of VFTs based on the type of cue: the letter fluency task (LFT) and the category fluency task (CFT). However, the fundamental aspects of brain connectivity across the frontotemporal regions during the VFTs have not been elucidated. In this study, we hypothesized that differences in cortical functional connectivity over the left and right frontotemporal regions may be observed by means of multichannel functional near-infrared spectroscopy (fNIRS) during the performance of LFT and CFT. Our results from fNIRS (ETG-4000) showed different patterns of brain functional connectivity during the two types of VFTs, which was consistent with the different cognitive requirements of each task. We demonstrate increased brain functional connectivity over the frontal and temporal regions during the LFT than during the CFT; these results are in line with previous brain activity studies using fNIRS to demonstrate higher frontal and temporal region activation during LFT and CFT, with more pronounced frontal activation by the LFT.