fMRI measures neural activity indirectly via ...

• A. Direct neuron firing
• B. Blood flow and oxygenation changes
• C. Synaptic vesicle release
• D. Muscle activity

Answer: (B)

Functional MRI measures neural activity indirectly through changes in blood flow and oxygenation in the brain. When a region is active, neurons demand more oxygen, and blood flow to that area increases, altering the balance of oxygenated and deoxygenated hemoglobin. These hemoglobin changes affect the MRI signal, producing what we call the BOLD signal. Because it tracks vascular responses rather than the exact electrical spikes of neurons, the reading is an indirect indicator of activity, with a slight delay after the neural firing. It doesn’t directly record neuron firing, synaptic vesicle release, or muscle activity, which would require other measurement methods.