Cerebral hemodynamic and oxygenation changes induced by inner and heard speech: a study combining functional near-infrared spectroscopy and capnography

Abstract

Abstract. The aim of this study was to investigate the effects of inner and heard speech on cerebral hemodynamics and oxygenation in the anterior prefrontal cortex (PFC) using functional near-infrared spectroscopy and to test whether potential effects were caused by alterations in the arterial carbon dioxide pressure (PaCO 2 ). Twenty-nine healthy adult volunteers performed six different tasks of inner and heard speech according to a randomized crossover design. During the tasks, we generally found a decrease in PaCO 2 (only for inner speech), tissue oxygen saturation (StO 2 ), oxyhemoglobin (½O 2 Hb), total hemoglobin ([tHb]) concentration and an increase in deoxyhemoglobin concentration ([HHb]). Furthermore, we found significant relations between changes in ½O 2 Hb, [HHb], [tHb], or StO 2 and the participants' age, the baseline P ET CO 2 , or certain speech tasks. We conclude that changes in breathing during the tasks led to lower PaCO 2 (hypocapnia) for inner speech. During heard speech, no significant changes in PaCO 2 occurred, but the decreases in StO 2 , ½O 2 Hb, and [tHb] suggest that changes in PaCO 2 were also involved here. Different verse types (hexameter and alliteration) led to different changes in [tHb], implying different brain activations. In conclusion, StO 2 , ½O 2 Hb, [HHb], and [tHb] are affected by interplay of both PaCO 2 reactivity and functional brain activity. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Modelling confounding effects from extracerebral contamination and systemic factors on functional near-infrared spectroscopy

“…Similarly, we cannot rule out a role for ${\mathrm{CO}}_2$ in the anagram results. While it is not immediately obvious what that role might be, it is known that unvocalised language tasks can induce changes in blood oxygenation and ${\mathrm{CO}}_2$ (Scholkmann et al, 2014a). In either case, more complete systemic data would allow a better assessment to be made of the extent to which these factors play a role in the fNIRS signals.…”

Time–frequency dynamics of the sum of intra- and extracerebral hemodynamic functional connectivity during resting-state and respiratory challenges assessed by multimodal functional near-infrared spectroscopy

“…Recent resting-state studies applying fNIRS simultaneously with fMRI [Duan et al, 2012;Niu and He, 2013;Sasai et al, 2012] or without fMRI [Niu et al, 2012;Zhang et al, 2011a;Zhang et al, 2011b] confirmed that fNIRS represents a reliable resting-state imaging method. The importance of measuring PaCO 2 during fNIRS recordings was also discussed recently [Holper et al, 2014a;Scholkmann et al, 2013a;Scholkmann et al, 2013b;Scholkmann et al, 2014b]. …”

Different mechanosensory stimulations of the lower back elicit specific changes in hemodynamics and oxygenation in cortical sensorimotor areas—AfNIRSstudy

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“…Changes in PetCO 2 can have significant impacts on fNIRS signals (Scholkmann, Gerber, Wolf, & Wolf, 2013;Scholkmann, Klein, Gerber, Wolf, & Wolf, 2014;. A main reason for this confounding effect in the fNIRS signal might have been that they did not apply short separation regression within their analyses in order to get rid of confounding hemodynamics of the extracerebral layers (Gregg, White, Zeff, Berger, & Culver, 2010;Saager & Berger, 2005).…”