Which statement about the relationship between fMRI signals and actual neural firing is true?

• A. fMRI signals reflect changes in blood flow and oxygenation with a delay.
• B. fMRI signals directly measure neuron firing.
• C. fMRI signals reflect only structural changes.
• D. fMRI signals measure neurotransmitter release.

Answer: (A)

The main concept being tested is that fMRI signals are indirect measures of neural activity, tied to hemodynamic changes rather than direct electrical firing. When neurons activate, they trigger a vascular response that increases blood flow and changes blood oxygenation in the region, but this hemodynamic response unfolds over several seconds. That means the fMRI BOLD signal reflects neural activity with a delay, not the instantaneous firing itself.

This is why the correct statement is best: it captures the idea that fMRI tracks blood flow and oxygenation changes that follow neural activity, rather than measuring neurons firing directly. It also explains why other descriptions don’t fit: fMRI does not directly measure action potentials, nor does it track static structural changes or neurotransmitter release.