Luminance contrast of a visual stimulus modulates the BOLD response more than the cerebral blood flow response in the human brain

• Published in: NeuroImage (Orlando, Fla.) Vol. 64; pp. 104 - 111
• Main Authors: Liang, Christine L., Ances, Beau M., Perthen, Joanna E., Moradi, Farshad, Liau, Joy, Buracas, Giedrius T., Hopkins, Susan R., Buxton, Richard B.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.01.2013; Elsevier; Elsevier Limited
• Subjects: Adult; Arterial spin labeling (ASL); Biological and medical sciences; Blood; Blood oxygen level dependent (BOLD) effect; Brain - physiology; Brain mapping; Brain Mapping - methods; Cerebral blood flow (CBF); Cerebral metabolic rate of oxygen consumption (CMRO2); Cerebrovascular Circulation - physiology; Eye and associated structures. Visual pathways and centers. Vision; Female; Functional magnetic resonance imaging (fMRI); Fundamental and applied biological sciences. Psychology; Humans; Magnetic Resonance Imaging - methods; Male; Medical imaging; Oxygen - blood; Oxygen Consumption - physiology; Photic Stimulation - methods; Reproducibility of Results; Sensitivity and Specificity; Standard deviation; Studies; Vertebrates: nervous system and sense organs; Visual contrast; Visual cortex; Young Adult; Cerebral metabolic rate of oxygen consumption (CMRO2); Visual contrast; Visual cortex; Arterial spin labeling (ASL); Functional magnetic resonance imaging (fMRI); Cerebral blood flow (CBF); Blood oxygen level dependent (BOLD) effect; Central nervous system; Stimulus luminance; Encephalon; Visual pathway; Functional magnetic resonance imaging; Coupling; Human; Regional blood flow; Oxygen; Cerebral metabolic rate of oxygen consumption (CMRO; ); Contrast; Nuclear magnetic resonance imaging; fMRI; Visual stimulus; Vision; Perception; Hemodynamics; Oxygenation; Functional imaging
• ISSN: 1053-8119; 1095-9572; 1095-9572
• DOI: 10.1016/j.neuroimage.2012.08.077

The blood oxygenation level dependent (BOLD) response measured with functional magnetic resonance imaging (fMRI) depends on the evoked changes in cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) in response to changes in neural activity. This response is strongly modulated by the CBF/CMRO2 coupling relationship with activation, defined as n, the ratio of the fractional changes. The reliability of the BOLD signal as a quantitative reflection of underlying physiological changes depends on the stability of n in response to different stimuli. The effect of visual stimulus contrast on this coupling ratio was tested in 9 healthy human subjects, measuring CBF and BOLD responses to a flickering checkerboard at four visual contrast levels. The theory of the BOLD effect makes a robust prediction—independent of details of the model—that if the CBF/CMRO2 coupling ratio n remains constant, then the response ratio between the lowest and highest contrast levels should be higher for the BOLD response than the CBF response because of the ceiling effect on the BOLD response. Instead, this response ratio was significantly lower for the BOLD response (BOLD response: 0.23±0.13, mean±SD; CBF response: 0.42±0.18; p=0.0054). This data is consistent with a reduced dynamic range (strongest/weakest response ratio) of the CMRO2 response (~1.7-fold) compared to that of the CBF response (~2.4-fold) as luminance contrast increases, corresponding to an increase of n from 1.7 at the lowest contrast level to 2.3 at the highest contrast level. The implication of these results for fMRI studies is that the magnitude of the BOLD response does not accurately reflect the magnitude of underlying physiological processes. Increasing stimulus contrast increases the coupling ratio of CBF and CMRO2 responses to a visual stimulus. [Display omitted]