title: The coupling of cerebral blood flow and oxygen metabolism with brain activation is similar for simple and complex stimuli in human primary visual cortex.
abstract: Quantitative functional MRI (fMRI) experiments to measure blood flow and oxygen metabolism coupling in the brain typically rely on simple repetitive stimuli. Here we compared such stimuli with a more naturalistic stimulus. Previous work on the primary visual cortex showed that direct attentional modulation evokes a blood flow (CBF) response with a relatively large oxygen metabolism (CMRO2) response in comparison to an unattended stimulus, which evokes a much smaller metabolic response relative to the flow response. We hypothesized that a similar effect would be associated with a more engaging stimulus, and tested this by measuring the primary human visual cortex response to two contrast levels of a radial flickering checkerboard in comparison to the response to free viewing of brief movie clips. We did not find a significant difference in the blood flow-metabolism coupling (n=%ΔCBF/%ΔCMRO2) between the movie stimulus and the flickering checkerboards employing two different analysis methods: a standard analysis using the Davis model and a new analysis using a heuristic model dependent only on measured quantities. This finding suggests that in the primary visual cortex a naturalistic stimulus (in comparison to a simple repetitive stimulus) is either not sufficient to provoke a change in flow-metabolism coupling by attentional modulation as hypothesized, that the experimental design disrupted the cognitive processes underlying the response to a more natural stimulus, or that the technique used is not sensitive enough to detect a small difference.
authors.affiliation: Department of Bioengineering and Medical Scientist Training Program, University of California San Diego, La Jolla, CA, USA; Center for Functional Magnetic Resonance Imaging, Department of Radiology, University of California San Diego, La Jolla, CA, USA.
authors.forename: Valerie E M
authors.initials: VE
authors.lastname: Griffeth
authors.affiliation: Department of Bioengineering and Medical Scientist Training Program, University of California San Diego, La Jolla, CA, USA; Center for Functional Magnetic Resonance Imaging, Department of Radiology, University of California San Diego, La Jolla, CA, USA.
authors.forename: Aaron B
authors.initials: AB
authors.lastname: Simon
authors.affiliation: Center for Functional Magnetic Resonance Imaging, Department of Radiology, University of California San Diego, La Jolla, CA, USA; Kavli Institute for Brain and Mind, University of California San Diego, La Jolla, CA, USA. Electronic address: rbuxton@ucsd.edu.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Buxton
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000502:physiology*; D001923:Brain Chemistry / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D010775:Photic Stimulation; D014793:Visual Cortex / Q000502:physiology*
keywords: Blood flow–oxygen metabolism coupling; Calibrated BOLD; Cerebral blood flow (CBF); Cerebral metabolic rate of oxygen (CMRO(2)); Functional MRI; Visual cortex