Differential regulation of fronto-executive function by the monoamines and acetylcholine.

The prefrontal cortex (PFC) is innervated by the monoamines, dopamine (DA), noradrenaline (NA), and serotonin, as well as acetylcholine, and the marked influence of these neurochemical systems on prefrontal working memory processes has been widely described. However, their potentially, differential contribution to prefrontal functioning is less well understood. This paper reviews evidence to support the hypothesis that these neurochemical systems recruit distinct fronto-executive operations. Direct comparison of the effects of manipulations of these neuromodulators within PFC on performance of an attentional set-shifting paradigm reveals their differential contribution to distinct task stages. Depletion of prefrontal serotonin selectively disrupts reversal learning but not attentional set formation or set shifting. In contrast, depletion of prefrontal DA disrupts set formation but not reversal learning. NA depletion on the other hand specifically impairs set-shifting, whereas its effects on reversal learning remain unclear. Finally, depletion of prefrontal acetylcholine has no effect on either set formation or set shifting but impairs serial reversal learning. Because these neurochemical systems are known to represent distinct states of stress, arousal, attention, and affect, it is postulated that they augment the different types of executive operation that are recruited and performed within these states via a synergistic interaction with the PFC.