Septal Modulation of Hippocampo-Entorhinal Cortex Loop

The hippocampus is a key structure involved in learning and memory. Information enters hippocampus through the entorhinal cortex which is the major input to the hippocampal circuit consisting of the dentate gyrus (DG) > CA3 > CA1. The main source of acetylcholine in the hippocampus is the medial septum area (MSA) and the diagonal band of Broca. Cholinergic modulation of hippocampal neurons is critical for formation of memory traces. However, the exact mechanism of septo-hippocampal interactions, spatial and temporal characteristics of the activation of hippocampal neurons in response to stimulation of neurons in the MSA remains unknown. Understanding of the relationship between the activity of MSA neurons and the efficiency of synaptic transmission in the cortical-hippocampal connections is an important task, since it helps to find patterns that determine the pathways of information transmission in the brain during learning and navigation. Here, we will focus on the role played by MSA activity and, in particular, acetylcholine release by MSA neurons in the modulation of synaptic excitatory pathways in the hippocampus.