ACETYLCHOLINE - A NEUROTRANSMITTER FOR LEARNING AND MEMORY

The cholinergic hypothesis claims that the decline in cognitive functi ons in dementia is predominantly related to a decrease in cholinergic neurotransmission. This hypothesis has led to great interest in the pu tative involvement of the cholinergic neurotransmission in learning an d memory processes. This review aims to assess the data of studies in which the role of acetylcholine (ACh) in cognitive functions was inves tigated. For this purpose, studies from three different fields of rese arch, namely: (1) behavioral pharmacology (effects of drugs on behavio r); (2) behavioral neuroscience (effects of brain lesions on behavior) ; and (3) dementia, are discussed separately. The experimental tools t hat have been used in pharmacological studies may appear to be inadequ ate to enable conclusions to be drawn about the involvement of ACh in learning and memory processes. Especially, the use of scopolamine as a pharmacological tool is criticized. In the field of behavioral neuros cience a highly specific cholinergic toxin has been developed. It appe ars that the greater and more specific the cholinergic damage, the few er effects can be observed at the behavioral level. The correlation be tween the decrease in cholinergic markers and the cognitive decline in dementia may not be as clearcut as has been assumed. The involvement of other neurotransmitter systems in cognitive functions is briefly di scussed. Taking into account the results of the different fields of re search, the notion that ACh plays a pivotal role in learning and memor y processes seems to be overstated. Even when the role of other neurot ransmitter systems in learning and memory is taken into consideration, it is unlikely that ACh has a specific role in these processes. On ba sis of the available data, ACh seems to be more specifically involved in attentional processes than in learning and memory processes.