The Ontogeny of Hippocampus-Dependent Memories

Abstract

The formation of memories that contain information about the specific time and place of acquisition, which are commonly referred to as "autobiographical" or "episodic" memories, critically relies on the hippocampus and on a series of interconnected structures located in the medial temporal lobe of the mammalian brain. The observation that adults retain very few of these memories from the first years of their life has fueled a long-standing debate on whether infants can make the types of memories that in adults are processed by the hippocampus-dependent memory system, and whether the hippocampus is involved in learning and memory processes early in life. Recent evidence shows that, even at a time when its circuitry is not yet mature, the infant hippocampus is able to produce long-lasting memories. However, the ability to acquire and store such memories relies on molecular pathways and network-based activity dynamics different from the adult system, which mature with age. The mechanisms underlying the formation of hippocampus-dependent memories during infancy, and the role that experience exerts in promoting the maturation of the hippocampus-dependent memory system, remain to be understood. In this review, we discuss recent advances in our understanding of the ontogeny and the biological correlates of hippocampus-dependent memories.

Keywords: critical periods; development; early-life stress; hippocampus; learning and memory; place cell sequences.

Figure 1.

a, Schematic representation of the entorhinal-hippocampal circuit in the rat. Sensory information reaches the three regions of the hippocampus (dentate gyrus [DG], CA3, and CA1) via the superficial layers of the entorhinal cortex (EC-L2). In turn, the output station CA1 and subiculum (SUB) project back to the deep layers of the entorhinal cortex (EC-L5), which broadcasts the hippocampal output to multiple cortical areas. b, A comparative timeline delineating relevant milestones in the structural and functional maturation of the hippocampus-dependent memory system of rodents.