The literature linking serotonergic transmission to ‘waiting’ is extensive. With respect to the 5CSRTT, genetic or pharmacological disruption of the serotonin transporter or administration of agents that elevate synaptic serotonin levels reduce premature responding,128, 134, 135 while depletion of brain serotonin has the opposite effect.116, 136, 137 Activation of serotonin-1A receptors137 or blockade of serotonin-2C receptors increases premature responding, while -2C agonists or -2A antagonists (the latter given systemically or into the prefrontal cortex) decrease premature responding,138–140 again supporting an oppositional relationship between serotonin-2A and -2C subtypes (albeit the direction of the relationships appear to be opposite to those described for reversal learning and DRL performance).
