Hippocampus vs Amygdala: Memory and Emotion Side by Side
What's the difference between the hippocampus and the amygdala?
Side view
The Short Answer
Both sit side by side deep inside each temporal lobe. The hippocampus forms memories of facts and events and builds mental maps of places. The amygdala detects emotional significance, especially threat, and triggers fear responses. They work as a team: the amygdala's signal makes the hippocampus store emotional events more strongly.
At a Glance
| Aspect | Hippocampus | Amygdala |
|---|---|---|
| Name | Greek for "seahorse", after its curved shape | Greek for "almond", after its shape |
| Location | Floor of the temporal lobe, curving backward | Just in front of the hippocampus, near the tip of the temporal lobe |
| Main job | Forming new memories of facts and events; spatial navigation | Detecting emotional significance, especially threats; triggering fear responses |
| Role in memory | Records what happened, where, and when | Makes emotional memories stronger and more vivid |
| Famous case | H.M., who could no longer form new long-term memories | S.M., who showed strikingly little fear of everyday threats |
| Linked conditions | Alzheimer's disease, amnesia | Anxiety disorders, and differences in autism |
Neighbours With Different Jobs
The hippocampus and amygdala are both part of the limbic system and lie next to each other in the medial (inner) temporal lobe, one pair in each hemisphere. They're so close that the front of the hippocampus almost touches the amygdala. Yet damage to each produces strikingly different problems.
The hippocampus is the brain's recorder of experience. It binds together the separate parts of an event - what you saw, where you were, what happened next - into a memory that can later be stored across the cortex. It also contains "place cells" that fire when an animal is in a particular location; their discoverer, John O'Keefe, shared the 2014 Nobel Prize for revealing this internal map.
The amygdala is the brain's relevance detector. It responds within a fraction of a second to things that might matter for survival - an angry face, a sudden movement, a snake-like shape - and sets off bodily responses through the hypothalamus. It's also involved in learning which things predict danger or reward.
The Clearest Evidence: A Double Dissociation
In 1995, Antoine Bechara and colleagues studied three patients. One had damage to both amygdalae, one to both hippocampi, and one to both structures. Each was shown a coloured slide that was repeatedly followed by a loud, startling noise.
- The patient with amygdala damage could say exactly which colour came before the noise - but their body never learned to react to it, showing no stress response when the colour appeared.
- The patient with hippocampus damage showed the opposite: their body learned to react to the colour, but afterwards they couldn't remember which colour it was.
- The patient with damage to both did neither.
This pattern - called a double dissociation - showed that knowing about an emotional event and feeling an emotional response to it depend on different structures.
How They Work Together
In everyday life, the two collaborate. When something emotionally intense happens, the amygdala signals - partly through stress hormones such as adrenaline - that the moment is important, and the hippocampus stores it more strongly. As James McGaugh's research has shown, this is why we remember emotional events, good and bad, more vividly than ordinary ones.
The hippocampus returns the favour by providing context. It helps the amygdala tell the difference between a lion at the zoo and a lion on the loose - the same sight, but very different meaning depending on where you are.
Common Confusions
"The amygdala stores emotional memories."
The amygdala strengthens emotional memories and stores learned emotional associations, but the detailed memory of what happened depends on the hippocampus and cortex.
"The hippocampus is only about memory."
It's also central to navigation and imagining future scenarios, and it helps regulate the body's stress response.
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Key Terms
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Sources & Further Reading
- Double dissociation of conditioning and declarative knowledge relative to the amygdala and hippocampus in humans - Bechara et al. (1995), Science
- The amygdala modulates the consolidation of memories of emotionally arousing experiences - McGaugh (2004), Annual Review of Neuroscience
- The Nobel Prize in Physiology or Medicine 2014 - NobelPrize.org
- The medial temporal lobe memory system - Squire & Zola-Morgan (1991), Science
- The human amygdala and the induction and experience of fear - Feinstein et al. (2011), Current Biology