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

• Published in: NeuroImage (Orlando, Fla.) Fla.), 2015-10, Vol.120, p.481-492
• Main Authors: Holper, L., Scholkmann, F., Seifritz, E.
• Format: Article
• Language: English
• Subjects: Adult; Anxiety; Brain; Breath Holding; Capnography; Carbon dioxide; Female; Functional near-infrared spectroscopy; Functional Neuroimaging; Hemodynamics - physiology; Humans; Hypercapnia - physiopathology; Hyperventilation - physiopathology; Hypocapnia - physiopathology; Hypoventilation - physiopathology; Male; Neurovascular Coupling - physiology; Partial pressure of carbon dioxide; Physiology; Prefrontal Cortex - physiology; Prefrontal Cortex - physiopathology; Respiration; Resting-state; Spectroscopy, Near-Infrared - methods; Spectrum analysis; Studies; Time–frequency dynamics of intra- and extracortical hemodynamic functional connectivity; Wavelet transforms
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2015.07.021

Monitoring respiratory processes is important for evaluating neuroimaging data, given their influence on time–frequency dynamics of intra- and extracerebral hemodynamics. Here we investigated the time–frequency dynamics of the sum of intra- and extracerebral hemodynamic functional connectivity states during hypo- and hypercapnia by using three different respiratory challenge tasks (i.e., hyperventilation, breath-holding, and rebreathing) compared to resting-state. The sum of intra- and extracerebral hemodynamic responses were assessed using functional near-infrared spectroscopy (fNIRS) within two regions of interest (i.e., the dorsolateral and the medial prefrontal cortex). Time–frequency fNIRS analysis was performed based on wavelet transform coherence to quantify functional connectivity in terms of positive and negative phase-coupling within each region of interest. Physiological measures were assessed in the form of partial end-tidal carbon dioxide, heart rate, arterial tissue oxygen saturation, and respiration rate. We found that the three respiration challenges modulated time–frequency dynamics differently with respect to resting-state: 1) Hyperventilation and breath-holding exhibited inverse patterns of positive and negative phase-coupling. 2) In contrast, rebreathing had no significant effect. 3) Low-frequency oscillations contributed to a greater extent to time–frequency dynamics compared to high-frequency oscillations. The results highlight that there exist distinct differences in time–frequency dynamics of the sum of intra- and extracerebral functional connectivity not only between hypo- (hyperventilation) and hypercapnia but also between different states of hypercapnia (breath-holding versus rebreathing). This suggests that a multimodal assessment of intra-/extracerebral and systemic physiological changes during respiratory challenges compared to resting-state may have potential use in the differentiation between physiological and pathological respiratory behavior accompanied by the psycho-physiological state of a human. •Hemodynamic changes were compared between hypo-/hypercapnia and resting-state.•Time–frequency dynamics were assessed using wavelet transform coherence.•Hyperventilation and breath-holding exhibited significant effects on phase-coupling.•Rebreathing had no effect on phase-coupling.•Results may support separating physio- from pathological respiratory behavior.