title: Investigating the post-stimulus undershoot of the BOLD signal--a simultaneous fMRI and fNIRS study.
abstract: Measuring the hemodynamic response with functional magnetic resonance imaging (fMRI) together with functional near-infrared spectroscopy (fNIRS) may overcome limitations of single-method approaches. Accordingly, we measured the event-related hemodynamic response with both imaging methods simultaneously in young subjects during visual stimulation. An intertrial interval of 60 s was chosen to include the prolonged post-stimulus undershoot of the blood oxygenation level dependent (BOLD) signal. During visual stimulation, the BOLD signal, oxy-, and total hemoglobin (Hb) increased, whereas deoxy-Hb decreased. The post-stimulus period was characterized by an undershoot of the BOLD signal, oxy-Hb, and an overshoot of deoxy-Hb. Total Hb as measured by fNIRS returned to baseline immediately after the end of stimulation. Results suggest that the post-stimulus events as measured by fNIRS are dominated by a prolonged high-level oxygen consumption in the microvasculature. The contribution of a delayed return of blood volume to the BOLD post-stimulus undershoot in post-capillary veins as suggested by the Balloon and Windkessel models remains ambiguous. Temporal changes in the BOLD signal were highly correlated with deoxy-Hb, with lower correlation values for oxy- and total Hb. Furthermore, data show that fNIRS covers the outer 1 cm of the brain cortex. These results were confirmed by simultaneous fMRI/fNIRS measurements during rest. In conclusion, multimodal imaging approaches may contribute to the understanding of neurovascular coupling.
authors.affiliation: Max-Planck-Institute for Human Cognitive and Brain Sciences, Stephanstr. 1A, Germany. schroet@cbs.mpg.de
authors.forename: Matthias L
authors.initials: ML
authors.lastname: Schroeter
authors.forename: Thomas
authors.initials: T
authors.lastname: Kupka
authors.forename: Toralf
authors.initials: T
authors.lastname: Mildner
authors.forename: Kâmil
authors.initials: K
authors.lastname: Uludağ
authors.forename: D Yves
authors.initials: DY
authors.lastname: von Cramon
mesh_terms: D000328:Adult; D001923:Brain Chemistry / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology; D003576:Electron Transport Complex IV / Q000378:metabolism; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006454:Hemoglobins / Q000737:chemistry; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D008297:Male; D010100:Oxygen / Q000097:blood*; D010775:Photic Stimulation; D019265:Spectroscopy, Near-Infrared / Q000706:statistics & numerical data*; D014793:Visual Cortex / Q000033:anatomy & histology / Q000098:blood supply
chemical_list: D006454:Hemoglobins; D003576:Electron Transport Complex IV; D010100:Oxygen