Using a combined optogenetic and viral tracing approach in a transgenic model of AD (Tg2576-APPswe mice), it was established that ChAT+ neurons (choline acethyltransferase neurons) + in the diagonal band of Broca directly innervates immature neurons of the dorsal hippocampus and that this connection is essential for cholinergic transmission and hippocampal neuron survival (Figure 4). Here, CHAT is linked to Alzheimer disease.