What is the nature of the role of the serotonergic nervous system in learning and memory: prospects for development of an effective treatment strategy for senile dementia.

The serotonergic nervous system has long been suspected of playing an important role in the processes underlying learning and memory. However, owing frequently to inconsistent and divergent results, its precise role is difficult to define. Recently, there has been a renewed interest in this neurotransmitter's role in the processes underlying learning and memory. This has, in part, been due to the observations that this system appears to undergo significant deterioration as a result of the pathology associated with certain age-related cognitive disorders as well as the discovery of multiple receptor subtypes. Reviewed here are the results of a number of studies designed to gain further insight into the role the serotonergic nervous system plays in learning and memory. A variety of methods are used to manipulate this system, and the effects of these manipulations on performance in a variety of behavioral tasks are summarized. Consistent with past observations, it is difficult to incorporate the results of the present series of studies into a single unified theory of serotonin's role in learning and memory. However, it is clear that not all of the inconsistencies can be attributed to differences in the methods used to manipulate the system or in the types of tasks used to assess learning and memory. Some of the inconsistencies clearly belie a selective role of this neurotransmitter in the processes underlying learning and memory and further underscore the complex nature of this system's role in the processing of information by the brain.