Neural Circuit Models of the Serotonergic System: From Microcircuits to Cognition

Serotonin (5-HT) is a key neuromodulator with strong putative roles in controlling the principles of economic and social decision making, reward/punishment learning, emotional regulation, performance monitoring, and response inhibition activities. Impairments in the serotonergic system have been associated with a range of disorders in the domains of psychiatry (LopezIbor, 1992), motor (Halliday, Blumbergs, Cotton, Blessing, & Geffen, 1990; Fox, Chuang, & Brotchie, 2009), sensory, proprioceptive, and homeostatis (Halford, Harrold, Lawton, & Blundell, 2005), and social behaviors (Crockett, Clark, Tabibnia, Lieberman, & Robbins, 2008). This includes addiction (Miszkiel, Filip, & Przegalinski, 2011), depression (Eshel & Roiser, 2010; Homberg, 2012), attention deficit hyperactivity disorder, anxiety (Wise, Berger, & Stein, 1972), impulsivity, bipolar disorder, impulsivity, obsessive compulsive disorder (Dalley, Everitt, & Robbins, 2011), Parkinson’s disease, chorea, Tourette’s syndrome, obesity, anorexia, and schizophrenia (Aghajanian & Marek, 2000).

This chapter reviews and gives pointers to major computational models of serotonergic systems at the level of microcircuits in the cortex and brain stem; and broadly for cognitive and decision making networks.

The Serotonergic System

The mammalian dorsal raphe nucleus (DRN), one of the raphe nuclei in the brain stem, contains the majority of forebrain-­ projecting 5-HT neurons (Azmitia & Segal, 1978; Descarries, Alain, & Watkins, 1975; Jacobs & Azmitia, 1992; Moore, Halaris, & Jones, 1978; Vertes, 1991). Serotonin receptors are widely spread around the basal ganglia (BG) and the cortex, which are the key areas involved in decision making. Seven major receptor families have been identified for 5-HT, labeled as 5-HT1 to 5-HT7 (Bradley et al., 1986).