IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 22, NO. 3, MAY/JUNE 2016 6801706 Functional Connectivity During Phonemic and Semantic Verbal Fluency Test: A Multichannel Near Infrared Spectroscopy Study Chun-Jung Huang, Po-Han Chou, Hao-Lin Wei, and Chia-Wei Sun Abstract—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 multi- channel 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 cog- nitive requirements of each task. We demonstrate increased brain functional connectivity over the frontal and temporal regions dur- ing 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. Index Terms—Verbal fluency tests, functional connectivity of brain, fNIRS. I. INTRODUCTION F UNCTIONAL near-infrared spectroscopy (fNIRS) is a recently developed technology for monitoring functional brain activity based on the absorption and scattering properties of near-infrared light. fNIRS allows non-invasive measurements of the spatiotemporal characteristics of neural activity in the frontotemporal region by measuring changes in the concentra- tions of oxy-hemoglobin (ΔHbO 2 ), deoxy-hemoglobin (ΔHb), and total hemoglobin (ΔHbT) [1], [2]. fNIRS has several advan- tages over existing imaging techniques, such as PET, SPECT, and fMRI, because it is noninvasive, is easy to administer, Manuscript received July 31, 2015; revised September 21, 2015, September 28, 2015, October 12, 2015, and October 24, 2015; accepted November 11, 2015. Date of publication December 22, 2015; date of current version April 1, 2016. This work was supported in part by the Taiwan National Science Council un- der Grant NSC 101-2628-E-009-026-MY3, Grant NSC 102-2321-B-009-002, Grant NSC 102-2622-E-009-007-CC3, Grant NSC 102-2627-E-010-001, Grant NSC 102-3011-P-010-003, and a grant from Ministry of Education, Aim for the Top University Plan in National Chiao Tung University 101W9866, and in part by grants from Taichung Veterans General Hospital, Taiwan (TCVGH- 1034001A, TCVGH-1044002B, and TCVGH-YM1040101). Chun-Jung Huang and Po-Han Chou have contributed equallly to this paper. (Corresponding au- thor: Chia-Wei Sun.) C.-J. Huang and C.-W. Sun are with the Department of Photonics, Na- tional Chiao Tung University, Hsinchu 300, Taiwan (e-mail: mortis1115.eo00@ g2.nctu.edu.tw; chiaweisun@nctu.edu.tw). P.-H. Chou and H.-L. Wei are with the Department of Psychiatry, Taichung Veterans General Hospital, Taichung 407, Taiwan (e-mail: phchou1980@gmail. com; yrbovlxh@yahoo.com.tw). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSTQE.2015.2503318 tolerates small movements, is inexpensive, and provides excel- lent time resolution and moderate spatial resolution [3]. To date, fNIRS has been applied in many studies to explore the functional integration among brain regions during different states, includ- ing resting and task states in normal people and patients with psychiatric disorders [4]–[9]. Verbal fluency tests (VFTs) are widely used frontal lobe neu- ropsychological tests and have been frequently used in various functional brain mapping studies [10]–[13]. There are two ver- sions of VFTs based on the type of cue used: category fluency task (CFT) requires the participant to generate words belonging to a specific semantic category, while during the letter fluency task (LFT), subjects were asked to retrieve words with certain phonemic properties, e.g., words beginning with a given let- ter [14]. These different search strategies pose the question of whether semantic and phonemic systems for word generation depend on different neural substrates. Previous studies have shown that lesions in the temporal lobe may lead to deficits in semantic function, whereas phonemic function depends on frontal regions, as well as temporal lobes [15]. There have been several studies investigating the differences in brain activity during both versions of VFTs in healthy indi- viduals or patients with schizophrenia [16]–[20]. However, the fundamental aspects of brain connectivity across spatial regions of the frontotemporal regions during either versions of the VFT have not been elucidated to date. To the best of our knowledge, only one NIRS study investigated functional connectivity during a VFT, but evaluated a limited area of the cortex [21]. Therefore, the objective of this study was to investigate the functional connectivity during two versions of the VFTs over a wider area of the bilateral frontotemporal regions using a 52- channel continuous wave (CW)-NIRS system (ETG-4000). The NIRS imaging technique is so-called functional optical topog- raphy. We hypothesized that differences in cortical functional connectivity over the left and right frontotemporal regions could be observed by means of multi-channel fNIRS during LFT and CFT. Moreover, we expected LFT to cause greater frontal cortex involvement than CFT due to the increased selection demands associated with retrieving words based on spelling rules, relative to word retrieval based on semantic categories. II. MATERIAL AND METHODS A. Study Participants Thirteen healthy individuals (six men and seven women) without any psychiatric disease screened by Mini-International 1077-260X © 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.