Which statement about the BOLD signal and neural activity is true?

Which statement about the BOLD signal and neural activity is true?

• A. The BOLD signal is a proxy for neural activity linked to blood oxygenation and has a delay.
• B. The BOLD signal directly measures neuron firing.
• C. The BOLD signal reflects brain temperature changes only.
• D. The BOLD signal measures white matter integrity.

Answer: (A)

The BOLD signal in fMRI is an indirect readout of neural activity that comes from neurovascular coupling: when a brain region becomes active, blood flow to that area increases and changes in oxygenation (more oxyhemoglobin, less deoxyhemoglobin) occur. These oxygenation changes affect the MR signal in T2*-weighted images, so the BOLD signal tracks blood oxygenation rather than firing rates directly. There is a built-in delay—the hemodynamic response—because the vascular system takes a few seconds to respond to neuronal activity, so the BOLD peak typically occurs several seconds after the neurons fire. This makes the BOLD signal a proxy for neural activity with a characteristic delay, rather than a direct measure of neuron firing or other factors like temperature changes or white matter structure.

The BOLD signal in fMRI is an indirect readout of neural activity that comes from neurovascular coupling: when a brain region becomes active, blood flow to that area increases and changes in oxygenation (more oxyhemoglobin, less deoxyhemoglobin) occur. These oxygenation changes affect the MR signal in T2*-weighted images, so the BOLD signal tracks blood oxygenation rather than firing rates directly. There is a built-in delay—the hemodynamic response—because the vascular system takes a few seconds to respond to neuronal activity, so the BOLD peak typically occurs several seconds after the neurons fire. This makes the BOLD signal a proxy for neural activity with a characteristic delay, rather than a direct measure of neuron firing or other factors like temperature changes or white matter structure.