Recalling when and where: How the brain processes episodic memory

Introduction

By Deborah Grainger

Neuroscientists based at MIT have recently identified a novel brain circuit that processes the ‘where’ aspect of memory. Pairing this with their previous work on how the brain remembers the ‘when’ component, we now possess a greater understanding of memory construction.

When you remember an event, you reassemble several separate pieces of information; as well as what happened and how you felt, you also collate data on when it took place and where. This form of memory is called episodic memory: the ability to recall a specific memory from your many previous experiences (which is undoubtedly incredibly useful to cognitive beings).

The hippocampus, a brain region well known for its critical role in memory processing, takes part in the formation of episodic memories. Though this function has been recognized for some time, it was not known precisely how the hippocampus handles the ‘when’ and ‘where’ aspects of an emerging memory.

A splitting of the ‘when’ and ‘where’ from a singular input was thought to occur within the hippocampus itself; however, the MIT team has now discovered this information enters the hippocampus as two separate streams, which originate from another region of the brain called the entorhinal cortex.

Islands (and oceans) in the stream

The entorhinal cortex sits at the base of the hippocampus and connects it to the neocortex (the outermost layer of the brain). It is home to some very interesting cell populations, including grid cells (which were also key to recent Nobel prize-winning work), head direction cells, and various other types of place cells. But more than just an internal global positioning system, the entorhinal cortex is also recognized for its role in both memory recording and recall.