THE ROLE OF SEROTONERGIC CHOLINERGIC INTERACTIONS IN THE MEDIATION OFCOGNITIVE-BEHAVIOR

Cholinergic systems have been linked to cognitive processes such as at tention, learning and mnemonic function. However, other neurotransmitt er systems, such as the serotonergic one, which may have only minor ef fects on cognitive function on their own, interact with cholinergic fu nction and their combined effects may have marked behavioural actions. Some studies have dealt with serotonergic-cholinergic interactions, b ut it is unclear whether both systems affect cognition directly or whe ther interactions at a behavioural level result from additional altera tions in non-cognitive factors. This distinction is difficult, since i t is possible that the diverse cholinergic and serotonergic systems se rve different roles in the mediation of cognitive processes, both at t he neuroanatomical and neurochemical level. Nevertheless, it is possib le that cholinergic systems primarily alter accuracy in cognitive task s, whereas serotonergic neurotransmission modulates behaviour by alter ing bias (motivation, motor processes). Whether serotonin alters accur acy or bias, however, may also depend on the cognitive process under i nvestigation: it is suggested that attention, stimulus processing and/ or arousal can be influenced by both cholinergic and serotonergic syst ems independently from each other. Cholinergic and serotonergic projec tions to cortex and thalamus may be of importance in the mediation of these cognitive processes. Serotonergic-cholinergic interactions could also be of importance in the mediation of learning processes and tria l-by-trial working memory. The data available do not allow an unambigu ous conclusion about the role of these interactive processes in the me diation of long-term reference memory. These processes may rely on ser otonergic-cholinergic interactions at the hippocampal level. It is con cluded that serotonergic-cholinergic interactions play an important ro le in the mediation of behavioural, including cognitive, performance, but that further studies are necessary in order to elucidate the exact nature of these interactions.