[Sally Le Page (OP)]

This week, we'll try to remember to answer this question from listener David:

"How much of the brain is memory?"

What do you think?

[Halc]

Short term memory is a function of the hippocampus, a small more-primitive structure near the center that accounts for maybe 2% of the brain mass.
Longer term is a function of mostly the temporal lobes, which are along the sides and account for maybe a quarter of the brain area. I say 'area' because the brain is essentially a 2 dimensional structure about the size of a cloth napkin, but wadded up to fit in your head.
Any way, memory is not the only thing going on in the temporal lobe. Most of the auditory processing also takes place there.

[evan_au]

Moving from the macro view of episodic memory to the micro view:

I suggest that memory is stored in the dendritic spines of neurons.
- Their size and quantity is modified through experience and training
- These appear throughout the brain, not just in the hippocampus and temporal lobes, but wherever there are synapses between neurons
- This reflects the fact that there are many kinds of memory, not just episodic memory (eg "Yesterday I went to the store and bought a pack of face-masks...")
- Memory also includes learned skills like walking, talking, eating, seeing and listening, which are mostly unconscious, but take up a large part of our brain volume.
- These skills need to be relearned after an injury or stroke.
- Some people call these learned skills "muscle memory", but control and coordination of these muscle activities is primarily in the brain

See: https://en.wikipedia.org/wiki/Dendritic_spine#Importance_to_learning_and_memory

[CliffordK]

I'm looking forward to hearing the TNS answer.

I'm with @evan_au, I think a large portion of the brain is used for memories. 

While there is some specialization of different parts of the brain, there is no "Grandmother Cell", with general distribution of memories.  And some plasticity of the brain to recover from damage.

https://qbi.uq.edu.au/brain-basics/memory/where-are-memories-stored

[evan_au]

there is no "Grandmother Cell"

I did hear that brain researchers had found a "Jennifer Anniston" cell.
- researchers were measuring responses of individual (or small groups of) neurons in a human brain
- In one patient (a real fan of "Friends"), they found cells that fired consistently for images or the name of Jennifer Anniston.

Some epilepsy sufferers have electrodes implanted in the brain in an attempt to locate the source of severe episodes
- This is a rare treasure-trove for brain researchers.

The Wikipedia article mentions the Jennifer Aniston association, but then uses another famous person as an example. I'm not sure if this was to reduce the focus on just one patient? (ie privacy concerns?)

See: https://www.nature.com/news/2005/050620/full/news050620-7.html
https://en.wikipedia.org/wiki/Grandmother_cell

[Sally Le Page (OP)]

We didn't forget to answer this on the show! Have a listen to what neuroscientist Amy Milton had to say:

https://www.thenakedscientists.com/podcasts/question-week/what-proportion-brain-stores-memory [nofollow]

[TommyJ]

Two areas of the brain are actively involved in remembering our experiences. The hippocampus is a storehouse of short-term memory, and the cerebral cortex is used for long-term storage.
It is not exactly concluded how long the hippocampus can keep memories (about 2 weeks or so).

Information is stored in engram neuron cells.

An engram is a trace left by an irritant. Taking a certain neurons’ processes, a repetitive signal (sound, smell, a certain environment, etc.) provokes some physical and biochemical changes in them.

When the stimulus is repeated, the ‘trace’ is activated. The cells in which it is present will recall the entire memory from the memory. In other words, engram neurons are responsible for accessing the recorded information, and in order for them to work, a key signal must act on them. The engrams can be quite small amount of neurons.

Thus, there is still a certain relationship between these two regions of the brain, and over time, the cerebral cortex takes on an increasingly important role in storing any memory.

Cortex uses large areas for recognition, reproduction, and presentation.

‘All over the cortex’ - yes, but what exactly is the percentage, depends. But it is proven, for instance, people, who are bilingual, have noticeably thicker cortex part. Hence, the percentage of brain occupied by memory depends a lot on how much you remember)

[EvaH]

Asked and answered on the show!

https://www.thenakedscientists.com/podcasts/question-week/what-proportion-brain-stores-memory