fMRI BOLD signal — MRCPsych Paper A MCQ

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EasyNeuroimaging, neuroendocrinology and psychoneuroimmunologyfMRI BOLD signalMRCPsych Paper A

A participant performs an emotional-face task during conventional task-based fMRI. Increased neural activity produces a local haemodynamic response that alters the concentration of deoxyhaemoglobin and, consequently, the magnetic resonance signal. Which measurement is used to generate the resulting activation map?

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Correct answer: A — Blood oxygen level-dependent contrast

The correct answer is A, blood oxygen level-dependent (BOLD) contrast. Conventional task-based fMRI does not directly record neuronal firing. Neural activity triggers neurovascular coupling, producing changes in local cerebral blood flow and oxygenation. Because oxyhaemoglobin and deoxyhaemoglobin have different magnetic properties, the resulting change in deoxyhaemoglobin alters the MR signal and provides an indirect correlate of neural activity. Extracellular action potentials require electrophysiological recording. Fractional anisotropy is derived from diffusion tensor imaging and characterises directional water diffusion, particularly in white-matter tracts. Regional 18F-FDG uptake is measured using positron emission tomography and reflects glucose metabolism. Cerebrospinal fluid tau is a fluid biomarker rather than an imaging signal.

Reference: Buxton RB. The physics of functional magnetic resonance imaging (fMRI). Reports on Progress in Physics. 2013;76(9):096601. https://pubmed.ncbi.nlm.nih.gov/24006360/