The MRI signal used to measure neural activity via changes in blood oxygenation is known as what?

• A. Hemodynamic response
• B. EEG signal
• C. T1-weighted signal
• D. Blood oxygen level-dependent signal

Answer: (D)

The main idea is how neural activity is detected with MRI through changes in blood oxygenation. The MRI signal that tracks those changes is the Blood Oxygen Level-Dependent signal, or BOLD. When a brain region becomes active, blood flow increases more than the oxygen it uses, lowering the amount of deoxyhemoglobin. Deoxyhemoglobin is paramagnetic and dampens the MR signal, so its reduction leads to a stronger signal on T2*-weighted images. That change in signal specifically reflects shifts in blood oxygenation tied to neural activity, which is why this readout is called the BOLD signal. It’s distinct from EEG, which measures electrical activity, and from T1-weighted MRI, which is primarily structural. The broader vascular response is the hemodynamic response, but the MRI signal used to monitor neural activity via oxygenation is the BOLD signal.