Lateralization of amygdala activation: a systematic review of functional neuroimaging studies.

Functional neuroimaging studies of emotion processing consistently report amygdala activation. Most of these studies observed lateralized amygdala activity, indicative of a clear hemisphere-specific processing difference between the left and right amygdalae. Because individual studies use varying paradigms and are limited by statistical power and sensitivity, it has remained unclear whether the left or the right amygdala is more consistently involved in emotional processing. By combining results across 54 fMRI and PET studies in a metaanalysis, we sought to establish if a common pattern of lateralized amygdala activation exists. Our findings indicate that across studies, the left amygdala is more often activated than the right amygdala, suggesting different roles for the left and right amygdalae in emotional processing. Further analysis showed that this predominant left amygdala activation is not significantly related to stimulus type, task instructions, differential habituation rates of the left and right amygdalae or elaborate processing. The results are discussed in relation to methodological and theoretical issues regarding functional brain asymmetry. Copyright 2004 Elsevier B.V.