Serotonin in Mood and Emotion

The topographical organization of serotonergic innervation of the forebrain, as well as the paracrine nature of serotonergic neurotransmission in limbic structures, support the contention that serotonin plays a neuromodulatory role in the brain. The lack of synaptic specializations at serotonergic terminals and varicosities in many brain regions suggests that serotonergic innervation may be particularly pliable. As conscious feeling or the cognitive aspect of emotion involves learning and memory, the serotonergic system may be particularly well suited for modulating mood. Pharmacological manipulations of serotonergic neurotransmission alter emotional processing, attentional bias, emotional memory, dysfunctional attitudes and decision-making. In healthy human subjects, increases in serotonergic neurotransmission result in enhanced attention and recognition of positive emotional material. Contrary to expectation, acute increases in serotonergic neurotransmission also increase attentional bias towards negative or fearful stimuli. In general, decreased serotonergic neurotransmission results in impaired attention and recognition of positive emotional material, and increases the attentional bias towards negative stimuli in healthy subjects. A polymorphism in the serotonin transporter gene also alters emotional processing. Understanding not only the neurobiology of emotional responses, but also serotonergic modulation of emotional states, will be important as we attempt to elucidate the etiology of emotional disorders. Future research with agents specific to various serotonin receptors may identify important therapeutic targets for the treatment of cognitive and affective disorders.