Hemispheric asymmetries in the amygdala: A comparative primer.

The amygdala is a core structure in the neuronal network underlying emotion processing in the vertebrate brain. Its structure and function have been extensively studied in both neuroimaging studies in human volunteers and comparative studies in animal models. Across different studies and research questions regarding the amygdala, one often-encountered finding is that the left and the right amygdala are not equivalent in terms of function and structure. Hemispheric asymmetries in the amygdala have been reported on many different levels, yet a systematic integration of these findings has been missing from the literature. Researchers in both cognitive and clinical neurosciences are often puzzled why they find a specific effect or association for the left but not the right amygdala, or vice versa. In this review article, we provide an integrated overview of existing basic and clinical findings regarding amygdala asymmetries in structure, connections, and functions. Importantly, the literature suggests that functional amygdala lateralization is determined by temporal characteristics, emotional valence, and perceptual properties. Furthermore, we highlight alterations of amygdala asymmetries reported in different patient groups, thereby allowing for a deeper understanding of atypical amygdala asymmetries. Lastly, we aim to provide guidelines and approaches concerning the interpretation of results for researchers investigating amygdala asymmetries.