These peptides play a key role in mammalian reproductive and social behavior, including our own. For example, Thomas Baumgartner and his colleagues at the University of Zurich Selleck BKM120 found that oxytocin squirted into

a person’s nose can enhance the sense of trust (Baumgartner et al., 2008). It does so by acting on the amygdala and the midbrain, two regions involved in fear, and the dorsal striatum, a region involved in behavioral feedback. Oxytocin appears to produce a different effect when administered to people with borderline personality disorder: it impedes trust and positive social behavior. Scientists have argued that the link between oxytocin and serotonin may be different in people with this disorder, who suffer from BI 6727 nmr social anxiety and sensitivity to rejection because of early experiences with a parent, a genetic predisposition, or both (Bartz et al., 2011 and Baumgartner et al., 2008). Bargmann extended Insel’s work by identifying an amazing signaling system in C. elegans that consists of one peptide, nematocin. Nematocin, which is biochemically related to oxytocin and vasopressin, disturbs not only the worms’ reproductive behavior

but simple sensory and motor behaviors as well. From a detailed analysis of C. elegans’ behavior ( Garrison et al., 2012 and Emmons, 2012), Bargmann has concluded that oxytocin and vasopressin increase the coherence and coordinated execution of mating behavior in worms. These findings suggest that the brain has specific mechanisms designed to promote positive social behavior. These mechanisms—which appear in organisms separated by 600 million years of evolution—are remarkably well conserved. Moreover, manipulation of the mechanisms can have a profound influence on social behavior. Robert Malenka of Stanford University and his colleagues have taken a fresh look at positive group behavior (Dölen et al., 2013). They point out that even though social behavior promotes group survival in species as diverse as worms, honeybees,

and humans, before it nevertheless costs the individual effort and energy. Social behavior must provide some reward to the individual organism, they reasoned: why else would it have been conserved through evolution? They tested their idea in mice and found that oxytocin modulates the release of serotonin into the nucleus accumbens. Serotonin, a chemical that promotes feelings of well-being, rewards the mice for positive social behavior. Thus, the reinforcement of positive social interaction in mice requires the coordinated activity of both oxytocin and serotonin. Giacomo Rizzolatti and his colleagues at the University of Parma in Italy (Rizzolatti et al., 1996) discovered a network of neurons in motor areas of the cortex of monkeys that mirror the actions of others. These neurons respond similarly under two conditions: when a monkey is performing an action and when the monkey observes another monkey or a person performing the same action.