A typical limitation of fMRI is?

• A. Use of ionizing radiation
• B. Very low spatial resolution
• C. Temporal resolution is limited by the hemodynamic response
• D. Requires invasive brain surgery

Answer: (C)

The main idea here is that fMRI’s timing is limited by the slow vascular response to neural activity. fMRI tracks the BOLD signal, which reflects changes in blood flow and oxygenation that follow neural firing. This vascular response rises and falls over several seconds after neurons become active, peaking around a few seconds later and smoothing over wider time windows. Because of this, we can’t pinpoint the exact moment a neural event happened; we can only infer activity within a window of a few seconds. That’s why temporal resolution is limited.

In contrast, fMRI does not use ionizing radiation and is non-invasive, and it provides relatively good spatial localization (unlike what some other modalities offer). So the option describing the temporal limit due to the hemodynamic response best captures the characteristic limitation of fMRI.