Functional near-infrared spectroscopy for the assessment of speech related tasks A.C. Dieler a,c,1 , S.V. Tupak a,1 , A.J. Fallgatter b,⇑ a Department of Psychiatry, Psychosomatics, and Psychotherapy, University Wuerzburg, Germany b Department of Psychiatry and Psychotherapy, University Tuebingen, Germany c Human Movement Science, Technische Universität München, Germany article info Article history: Available online 19 April 2011 Keywords: Near-infrared spectroscopy fNIRS Language Verbal fluency Lateralization Comprehension Perception abstract Over the past years functional near-infrared spectroscopy (fNIRS) has substantially contributed to the understanding of language and its neural correlates. In contrast to other imaging techniques, fNIRS is well suited to study language function in healthy and psychiatric populations due to its cheap and easy application in a quiet and natural measurement setting. Its relative insensitivity for motion artifacts allows the use of overt speech tasks and the investigation of verbal conversation. The present review focuses on the numerous contributions of fNIRS to the field of language, its development, and related psychiatric disorders but also on its limitations and chances for the future. Ó 2011 Elsevier Inc. All rights reserved. 1. General introduction Functional near-infrared spectroscopy (fNIRS) has been applied to various fields of neurophysiological research since its introduc- tion in the late 1970s by Jöbsis (1977). Several advantages like its relative insensitivity to movement, portability and affordability provide the researcher with freedom in task design and the possibility to study populations like patients, children or elderly, known to be problematic in settings like func- tional magnetic resonance imaging (fMRI) or electroencephalogra- phy (EEG) studies which require the subject to sit or lie still (i.e. EEG) in a very narrow and noisy environment (i.e. fMRI). These advantages make it especially useful in the field of language re- search and this review will, to our knowledge for the first time, try to comprehensively introduce the reader to the current status of knowledge in the field of language, its anatomy, development, as well as related disorders within neurology and psychiatry as ac- quired with fNIRS. The review will give a short introduction into the methodology of fNIRS, its principles, advantages and disadvantages. Subse- quently its contributions to researching the neuroanatomical and neurophysiological correlates of language, like lateralization effects, areas isolated as being responsible for the comprehension and per- ception and their development from an early age on, as well as to the related concept of reading will be highlighted by summarizing studies contributing to the understanding of these processes by the use of fNIRS. In the remainder of this article the authors will out- line studies focusing on language-related disorders in the fields of neurology (i.e. aphasia and epilepsy) and psychiatry (i.e. disruptions of speech production in mood disorders, schizophrenia, dementia and anxiety disorders, as well as dyslexia and vigilance). 1.1. Literature search criteria Studies included in the present review were derived from scholar.google.com and http://www.ncbi.nlm.nih.gov/pubmed/ be- tween February 1st and March 1st 2010. Keywords were (1) near- infrared spectroscopy, fNIRS or optical topography combined with (2) language (l), l comprehension, l perception, l development, l lat- eralization, l localization, reading, speech, talking, verbal fluency, VFT, or word fluency. 2. Introduction to functional near-infrared spectroscopy 2.1. Fundamentals of fNIRS Since its introduction in the late 70s (Jöbsis, 1977) and the devel- opment of multichannel apparatuses in the late 80s and early 90s, functional near-infrared spectroscopy (fNIRS) has been increasingly used to study human brain function in adults (Hoshi & Tamura, 1993; Kato, Kamei, Takashima, & Ozaki, 1993; Villringer, Planck, Hock, Schleinkofer, & Dirnagl, 1993) and infants (Chance et al., 1988). fNIRS employs near-infrared light to non-invasively measure changes in the concentration of oxygenated (O 2 Hb), deoxygenated 0093-934X/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.bandl.2011.03.005 ⇑ Corresponding author. Fax: +49 7071 294141. E-mail address: Andreas.Fallgatter@med.uni-tuebingen.de (A.J. Fallgatter). 1 Both authors contributed equally to this article. Brain & Language 121 (2012) 90–109 Contents lists available at ScienceDirect Brain & Language journal homepage: www.elsevier.com/locate/b&l