Acetylcholine, a well known neurotransmitter, plays a critical synaptic role in the initial formation of memory. Chemical blockage of the acetylcholine receptors makes it harder to learn and remember even in healthy young people. Evidence for it comes from pharmacological studies conducted on human subjects wherein blockage of muscarinic cholinergic receptors by drugs such as scopolamine impaired the encoding of new memories. Conversely, drugs which activated nicotinic receptors enhanced the encoding of new information.
Similarly administration of scopolamine into the hippocampus impaired encoding of spatial memory. It has also been found that administration of drug that increases the level of acetylcholine in Alzheimer's disease (characterised of memory problems) improves memory by inhibiting the action of acetyl cholinesterase, an enzyme that breaks down acetylcholine and reduces its amount. Overall it can be said that decreased acetylcholine in the brain cause problems with memory function.