Hippocampus function: memory, navigation, and stress

The hippocampus is a seahorse-shaped brain structure that files new experiences into long-term memory and helps you find your way around. You actually have two, one in each temporal lobe, working closely with the amygdala to tag where, when, and how emotionally charged an experience was. Chronic stress can disrupt it, but it stays capable of change throughout life.

Where is the hippocampus, and what does it do?

Each hippocampus curls through a temporal lobe, roughly level with your ears, with one in the left hemisphere and one in the right. The name comes from the Greek word for “seahorse,” a nod to its curved shape on a brain scan.

A 2023 anatomy review from StatPearls, hosted on the NIH’s NCBI Bookshelf, describes its main job as converting short-term experience into long-term memory you can consciously recall. It also plays a lead role in spatial navigation. It works closely with the amygdala, which tags how emotionally intense a moment felt. Both sit at the core of the limbic system, the brain network most involved in emotion and memory.

How does stress affect the hippocampus?

Chronic stress plays a real role here. A 2006 review in Dialogues in Clinical Neuroscience by psychiatrist J. Douglas Bremner describes how sustained exposure to stress hormones like cortisol can disrupt hippocampal function. That disruption is part of why an intensely stressful memory can end up feeling fragmented instead of clearly timestamped. Our traumatic memory entry covers this in more depth.

The story isn’t simply “stress shrinks your hippocampus,” though. A 2002 twin study in Nature Neuroscience found that combat veterans with more severe PTSD tended to have smaller hippocampal volume. Their identical twins, who had never been to combat, tended to have smaller hippocampal volume too. Because twins share the same genes, that points to smaller hippocampal volume as a pre-existing trait that raises vulnerability, not only damage trauma causes.

Can the hippocampus change and grow back?

Yes, and it’s the encouraging part of the research. A landmark 2000 study in the Proceedings of the National Academy of Sciences scanned London taxi drivers and found the navigation-related part of their hippocampus was measurably larger than in non-drivers. That same region was larger still in drivers with more years on the job, evidence of the brain adapting to intense spatial demands. That kind of structural change is what neuroscientists call neuroplasticity: the brain’s capacity to reorganize itself throughout life, not just in childhood.

Why does the hippocampus matter for EMDR and bilateral stimulation?

The hippocampus normally stamps a memory with “this happened, and it’s over,” which is why researchers studying PTSD look closely at how well it’s doing that job. When the tagging is disrupted, a memory can stay activated instead of settling into the past. Memory reconsolidation research describes a window where a retrieved memory becomes briefly editable, which is part of what EMDR’s bilateral stimulation is thought to work with. EmEase, a self-guided EMDR app, offers this bilateral-stimulation practice for everyday stress at app.emease.com.

Frequently asked questions

What is the main function of the hippocampus?

Its main job is turning short-term experience into long-term memory you can consciously recall, plus helping you navigate physical space. It works closely with the amygdala, which tags how emotional a moment felt, and both sit at the core of the limbic system, the brain's emotion-and-memory network.

Where is the hippocampus located?

You have two, one curling through each temporal lobe, roughly level with your ears. The name comes from the Greek word for seahorse, a nod to its curved shape on a brain scan. Together with the amygdala and hypothalamus, it anchors the limbic system.

Does stress shrink the hippocampus?

Chronic stress hormones like cortisol can disrupt hippocampal function, per a 2006 review in Dialogues in Clinical Neuroscience. But a 2002 twin study in Nature Neuroscience found smaller hippocampal volume can also be a pre-existing trait that raises PTSD vulnerability, not only damage trauma itself causes.

Can the hippocampus grow or change over time?

Yes. A landmark study of London taxi drivers, published in the Proceedings of the National Academy of Sciences, found the navigation-related part of their hippocampus was measurably larger than in non-drivers, and larger still in those with more years on the job, a clear example of the brain's neuroplasticity.

How does the hippocampus relate to EMDR?

The hippocampus normally tags a memory as finished and places it in the past. When that tagging is disrupted, a memory can stay activated instead of settling. EMDR's bilateral stimulation is thought to work within a similar window, called memory reconsolidation, where a retrieved memory becomes briefly editable.

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