Research on memory enhancing effects of acetylcholinesterase (AChE) inhibitors was stimulated by the finding of diminished cholinergic markers in patients with Alzheimer's disease, and the correlation of cognitive impairment to cholinergic deficits in these patients. The rationale for the use of AChE inhibitors is based on their abilities to prevent breakdown of acetylcholine released from surviving nerve terminals. In experimental animals the AChE inhibitor has been found by some investigators to be efficacious in improving cognitive function. Recent work has focused more on the performance and memory enhancing effects of tetrahydroaminoacridine (THA). THA has been found to improve performance in experimental animals with cognitive impairments induced by a variety of experimental manipulations such as by pharmacological blockade, cholinergic lesions, chronic alcohol or barbital treatment and ischemic lesion. These findings are compatible with the view that AChE inhibitors can be efficacious in "restoration" of some cholinergic functions.