We then proceed to advanced methods where fluorescent genetically encoded IEG reporters are chronically followed in vivo during memory formation. We begin with classical techniques, immunohistochemical detection of protein and fluorescent in situ hybridization of mRNA. In this review we present the overview of IEG mapping studies of retrosplenial cortex in rodent models. Imaging of the IEGs might therefore provide a picture of an emerging memory engram. There is a widely accepted consensus that their expression level corresponds to the engagement of individual neurons in the formation of memory trace. In the central nervous system they are rapidly triggered by neuronal activity and plasticity during learning. The common feature of this diverse group of genes is fast upregulation of their mRNA translation upon physiologically relevant stimulus. One of the most successful techniques is based on the analysis of brain expression patterns of the immediate early genes (IEGs). Several methodological approaches have been established over decades in order to investigate the cortical aspects of memory. One of the most widely studied regions is the retrosplenial cortex (RSC), an area in the parietal lobe densely interconnected with the hippocampal formation. Their relative contribution is a subject of intense research in both humans and animal models. Apart from the hippocampus, several cortical structures participate in this process.

It is served by an overlapping brain circuit, centered around the hippocampus (HPC) where the cognitive map index is stored. Spatial memory, the ability to remember the layout of the external environment and to navigate within its boundaries, is closely related to the autobiographical memory domain. The ability to form, retrieve and update autobiographical memories is one of the most fascinating features of human behavior.

Focus on human brain mapping