Beyond c-fos expression – neuronal activity of engram cells

Manuel Mittag1, Stefanie Poll1, Martin Fuhrmann1


Expression of immediate early genes (IEGs) like c-fos is associated with neuronal activity and often utilized to find and target specific neuronal ensembles. Episodic memories are encoded by sparse neuronal populations in the hippocampus, also called engrams. IEG-dependent optogenetic manipulation of engram neurons revealed them indispensable and sufficient for the retrieval of a specific memory trace. However, the relationship between c-fos expression and its underlying neuronal activity is not yet fully understood. We combine in vivo Ca2+-recording in awake c-fos-reporter mice that allow us to subsequently assess c-fos expression in a defined neuronal population in the hippocampus. Hereby we are able to determine the underlying Ca2+ activity of c-fos expressing CA1 neuronal ensembles during hippocampus-dependent encoding and investigate how experience-dependent changes of IEGs correlate with neuronal activity.