UC San Diego

The medial septum (MS) projects to the hippocampus (HC) and is involved in generating hippocampal theta. Two distinct populations of neurons in the MS have been the main focus of study, GABAergic parvalbumin (PV) and cholinergic neurons. GABAergic MS neurons project to HC inhibitory interneurons while cholinergic neurons project directly to pyramidal and interneuron cell types in HC. We discovered that optogenetically controlling MS PV neurons directly controlled the frequency of HC theta and shifting MS PV impairs memory in a hippocampal-dependent memory task. On the contrary, cholinergic neurons had no effect on HC theta power or theta frequency, and did not lead to deficits in a spatial memory task at various MS stimulation frequencies.