How Memory Works
What part of the brain controls memory?
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The Short Answer
No single region controls memory. The hippocampus is essential for forming new memories of facts and events, but long-term memories are stored across the cerebral cortex. The frontal lobe holds information in mind from moment to moment, the amygdala makes emotional events stick, and skills are learned by the basal ganglia and cerebellum.
Who Does What
| Brain region | Its role in memory |
|---|---|
| Frontal Lobe | Working memory: holds a phone number or the start of a sentence in mind for seconds, and organises what to remember and how to search for it. |
| Hippocampus | Forms new memories of events and facts by binding together where, when, and what happened. Also builds mental maps of places. |
| Temporal Lobe | Long-term storage of knowledge, such as the meanings of words and facts about the world (semantic memory). |
| Amygdala | Strengthens memories of emotionally charged events, which is why frightening or joyful moments are remembered so vividly. |
| Thalamus | Relays memory signals between the hippocampus and the cortex; damage here can cause severe amnesia. |
| Basal Ganglia | Learns habits and routines - the sequence of steps you no longer have to think about. |
| Cerebellum | Learns precisely timed movements and skills, such as riding a bike or playing a scale. |
Not One Memory, But Several
"Memory" covers several different abilities, and the brain handles them with different systems. Scientists usually distinguish between:
- Working memory - holding information in mind for a few seconds while you use it, such as a number you're about to dial.
- Episodic memory - memories of personal experiences: what you had for breakfast, or your last birthday.
- Semantic memory - general knowledge, such as the capital of France or what a "zebra" is.
- Procedural memory - skills and habits, such as typing or tying shoelaces, which you perform without consciously recalling how.
Episodic and semantic memories are sometimes grouped together as "explicit" memories, because you can consciously bring them to mind. Procedural memories are "implicit": you show them by doing, not by describing.
From Experience to Lasting Memory
Forming a long-term memory happens in stages. First, information is encoded: the hippocampus links together the separate pieces of an experience - the sights, sounds, place, and feelings processed in different parts of the cortex - into a single memory trace. Next comes consolidation, when that fragile trace is strengthened. Much of this happens during sleep: during deep sleep, the hippocampus appears to "replay" the day's experiences, helping transfer them into longer-lasting storage in the cortex. Finally, retrieval brings the memory back, with the frontal lobe helping to guide the search.
Over months and years, many memories seem to become less dependent on the hippocampus, which is why people with hippocampal damage can often still recall their childhood. Exactly how far this transfer goes - and whether vivid personal memories ever become fully independent of the hippocampus - is still debated.
Working memory is very limited. A famous 1956 paper by George Miller suggested we can hold about "seven, plus or minus two" items; later research suggests the true limit is closer to four meaningful chunks. Grouping information into chunks - remembering 07700 900 123 rather than eleven separate digits - is how we get around it.
Landmark Discoveries
The modern science of memory began with one patient. In 1953, Henry Molaison ("H.M.") had much of both hippocampi and the surrounding tissue removed to treat severe epilepsy. Afterwards he could hold a conversation and remember his childhood, but he could no longer form new long-term memories. Psychologist Brenda Milner showed he could still learn new motor skills, improving at a mirror-drawing task day after day without remembering having practised - proof that skill memory relies on different circuits from memory for facts and events.
Studies of people with exceptional memories have been just as revealing. A 2003 study by Eleanor Maguire and colleagues found that top competitors in memory championships didn't have unusual brain structure or higher intelligence. Instead, almost all used a learned strategy, the "method of loci" or memory palace: imagining items placed along a familiar route. While memorising, they engaged brain regions involved in spatial memory and navigation, including the hippocampus.
Common Myths
"Memory works like a video recording."
Memories are rebuilt each time they're recalled, and they can change in the process. In a classic 1974 experiment, Elizabeth Loftus and John Palmer showed people a film of a car accident. Those asked how fast the cars were going when they "smashed" into each other gave higher speed estimates than those asked about cars that "hit" each other - and a week later, they were more than twice as likely to falsely remember seeing broken glass.
"Some people have a photographic memory."
There's no convincing evidence that any adult can recall pages of text like a photograph. People with extraordinary memories almost always rely on practised techniques, as the memory champions above did.
"Memories are stored in one place."
A single memory is spread across many regions: the sights of an event in visual areas, the sounds in auditory areas, the emotion via the amygdala. The hippocampus acts more like an index that ties these pieces together than a storage box.
When It Goes Wrong
These conditions affect memory in different ways, depending on which part of the network is involved:
- Amnesia - A memory disorder involving the inability to recall past information (retrograde) or form new memories (anterograde), most often caused by damage to the hippocampus or thalamus.
- Alzheimer's Disease - A progressive neurodegenerative disease and the most common cause of dementia, marked by early memory loss and the gradual buildup of abnormal proteins in the brain.
- Traumatic Brain Injury - Damage to the brain caused by an external force - such as a blow, jolt, or penetrating injury - ranging from mild concussion to severe, life-altering injury.
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Sources & Further Reading
- Brain Basics: Know Your Brain - National Institute of Neurological Disorders and Stroke
- The medial temporal lobe memory system - Squire & Zola-Morgan (1991), Science
- The legacy of patient H.M. for neuroscience - Squire (2009), Neuron
- Working memory - Baddeley & Hitch (1974), Psychology of Learning and Motivation
- The magical number 4 in short-term memory: a reconsideration of mental storage capacity - Cowan (2001), Behavioral and Brain Sciences
- The memory function of sleep - Diekelmann & Born (2010), Nature Reviews Neuroscience
- The amygdala modulates the consolidation of memories of emotionally arousing experiences - McGaugh (2004), Annual Review of Neuroscience
- Routes to remembering: the brains behind superior memory - Maguire et al. (2003), Nature Neuroscience
- Reconstruction of automobile destruction: an example of the interaction between language and memory - Loftus & Palmer (1974), Journal of Verbal Learning and Verbal Behavior