The lateral habenula also projects to the median and dorsal raphe nuclei, which contain serotonin neurons and regulate emotions (80). In addition, electrical stimulation of the lateral habenula inhibits serotonin neurons (81), which is consistent with a role for this anatomical structure in depression and anxiety (82). Thus, the lateral habenula, which is activated by aversive stimuli (including stress) (83) and linked with negative emotions and whose activation is further linked with drug relapse could be involved in mechanisms underlying the high relapse rate linked with negative mood and/or stress exposures. There are no reported imaging studies on the habenula in addiction, which is likely to reflect in part the small size of this brain region, which makes it difficult to image.
