title: Greater contribution of cerebral than extracerebral hemodynamics to near-infrared spectroscopy signals for functional activation and resting-state connectivity in infants.
abstract: While near-infrared spectroscopy (NIRS) has been increasingly applied to neuroimaging and functional connectivity studies in infants, it has not been quantitatively examined as to what extent the deep tissue (such as cerebral tissue) as opposed to shallow tissue (such as scalp), contributes to NIRS signals measured in infants. A method for separating the effects of deep- and shallow-tissue layers was applied to data of nine sleeping three-month-old infants who had been exposed to 3-s speech sounds or silence (i.e., resting state) and whose hemodynamic changes over their bilateral temporal cortices had been measured by using an NIRS system with multiple source-detector (S-D) distances. The deep-layer contribution was found to be large during resting [67% at S-D 20 mm, 78% at S-D 30 mm for oxygenated hemoglobin (oxy-Hb)] as well as during the speech condition (72% at S-D 20 mm, 82% at S-D 30 mm for oxy-Hb). A left-right connectivity analysis showed that correlation coefficients between left and right channels did not differ between original- and deep-layer signals under no-stimulus conditions and that of original- and deep-layer signals were larger than those of the shallow layer. These results suggest that NIRS signals obtained in infants with appropriate S-D distances largely reflected cerebral hemodynamic changes.
authors.affiliation: Hitachi, Ltd. , Central Research Laboratory, 2520 Akanuma, Hatoyama, Saitama 350-0395, Japan.
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Funane
authors.affiliation: Tokyo Metropolitan University , Department of Language Sciences, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Fumitaka
authors.initials: F
authors.lastname: Homae
authors.affiliation: The University of Tokyo , Graduate School of Education, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Hama
authors.initials: H
authors.lastname: Watanabe
authors.affiliation: Hitachi, Ltd. , Central Research Laboratory, 2520 Akanuma, Hatoyama, Saitama 350-0395, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Kiguchi
authors.affiliation: The University of Tokyo , Graduate School of Education, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Gentaro
authors.initials: G
authors.lastname: Taga
keywords: functional connectivity; multidistance optodes; near-infrared spectroscopy; neuroimaging in infant; speech processing; superficial tissue contribution