Large-Vessel Venous Signal Confounds Apparent Amygdala Activation in BOLD fMRI

Recent BOLD fMRI studies have suggested that the amygdala exhibits heightened activity during emotional and mood-related tasks. However, modern imaging techniques have revealed that the hemodynamic properties of the blood-oxygen-level-dependent (BOLD) signal can obscure the true location of amygdala activation. In a new study, researchers found that apparent amygdala BOLD signal in a variety of tasks is largely influenced by nearby deep veins, such as the basal vein of Rosenthal.

This finding contradicts previous research, which suggested that the amygdala was the primary source of the venous signal when it was active.

Contrary to earlier work, the study demonstrates that the amygdala actually leads the venous signal, but it is not the sole contributor. The venous signal remains sensitive to amygdala engagement, but it is not specific to the amygdala. This confounding factor leads to inaccurate spatial localization of activation and hinders the precise attribution of signal to specific amygdala subnuclei using conventional BOLD fMRI.

Moreover, spatial smoothing exacerbates the problem by blending venous signal from the surrounding area with the actual anatomical amygdala, further mislocalizing the activation.

The researchers validated their findings by conducting the same experiments on a larger dataset from the Human Connectome Project. While broad conclusions about amygdala engagement can generally be considered reliable when based on unsmoothed signal within the anatomical amygdala, more nuanced insights into subnuclear function derived from conventional fMRI alone should be approached with caution.