fMRI measures brain activity indirectly, namely by measuring change in oxygen content; this is called the Blood Oxygenation Level Dependent (BOLD) contrast mechanism.
However, fMRI has certain limitations. For instance, the fMRI signal reflects changes in oxygen content with high but insufficient spatial-time resolution. Hemodynamics in response to neuronal activity is revealed on a spatial-temporal scale far longer than the neuronal activity itself. Here, so-called temporal "blurring" of the fMRI signal is caused by both inertance and residual effects. In spite of such obstacles, changes in neural activity associated with individual trials or components of a trial in a task can be observed. Moreover, it is possible to capture brain activity associated with a single momentary cognitive act of mentally rotating a stimulus, without recourse to averaging over events (Buckner & Logan 2001, p. 31). Special fMRI experimental designs such as event-related fMRI designs are required in these cases.
There are numerous difficulties in separating the processing roles of specific brain areas. Usually such separation is provided either by well matched task comparisons or through convergence across multiple studies. ...Show more