Acetylcholine and the cholinergic system contribute to learning and memory. In particular, the septohippocampal cholinergic system appears to be a critical neural substrate of working memory processes. Alterations of this system induced by anticholinergic drugs, electrolytic or neurotoxic lesions of this system produce impairments in working memory without disrupting reference memory. Clinical evidence also supports a role for degenerates in Senile Dementia of the Alzheimer Type. Working memory is involved in temporarily maintaining representations of previously experienced events or episodes, whereas reference memory contributes to the performance of well-learned responses in the presence of an appropriate discriminative stimulus. This component theory of memory serves to provide a conceptual framework for interpreting the dissociation in memory processes observed in both humans and animals following damage to the hippocampal formation or to its cholinergic innervation. Dr. Thomas Walsh is combining both pharmacological and behavioral experiments on rats in order to define the interactions between two transmitters GABA and acetylcholine in the modulation of synaptic activity in the hippocampus.