What is neuroplasticity?

I was asked this question on Quora:

Can you explain to a layman what neuroplasticity entails?

Neuroplasticity is the umbrella term for all of the brain’s mechanisms for learning and memory.

Since the average layperson already knows about learning and memory, I’m not sure whether there are any interesting implications.

Unless of course you are surprised that the brain is involved in learning and memory. Then the implications are vast. 🙂

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Is a memory a bunch of atoms? And does this mean we can transfer exact memories?

I was asked the following question on Quora.

Are specific memories just arrangements of atoms in our brains? Could you put certain molecules in someones head and give them an exact memory that you had?

Short answer: No.

Modern science has shown that every thing is an arrangement of atoms: neurons, apples, tables, rockets, asteroids, aardvarks… they are all made up of atoms.

The question now is this: is a memory a thing?

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No New Neurons? No Problem!

This answer was written in response to the following Quora question:

New research has found no neurogenesis in human adults, could this mean there is none or could it mean that neural stem cells are undetectable with the used techniques? What are your thoughts on this?

It’s good that you’re thinking of such things, since that is exactly what researchers themselves have to do, and what reviewers do. In order to show that the method works, there have to be adequate controls as part of the experiment.

And this is in fact the case. The paper would not have been published without controls.

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Perhaps neurogenesis doesn’t happen in adult humans?

A new study suggests that new neurons are not born very often in human adults.

Birth of New Neurons in the Human Hippocampus Ends in Childhood

“The lab’s new research, based on careful analysis of 59 samples of human hippocampus from UCSF and collaborators around the world, suggests new neurons may not be born in the adult human brain at all. The findings present a challenge to a large body of research which has proposed that boosting the birth of new neurons could help to treat brain diseases such as Alzheimer’s disease and depression. But the authors said it also opens the door to exciting new questions about how the human brain learns and adapts without a supply of new neurons, as in seen in mice and other animals.”

My labmates are all monkey neuroanatomists, and for years they have been skeptical about the neurogenesis narrative, particularly in primates. Another famous dissenter is Pasko Rakic. Read about his complaints in this Guardian article from 2012:

Does your brain produce new cells?


Why human memory is not a bit like a computer’s

My latest 3QD essay is about the mystery of human memory, and why it is not at all like computer memory. I discuss the quirks of human memory formation and recall, and the concept of “content-addressable memory”.

3quarksdaily: Why human memory is not a bit like a computer’s

Here is an excerpt:

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Synesthesia — secret passageways in the mansion of memory?

This post is a slightly modified version of my answer to a Quora question:

Is there a link between synesthetia and involuntary memory?

This is a very interesting question. I can add some neuroscientific flesh to the skeleton you have already laid out.

Involuntary memory seems to involve the ability for memories to be accessed via sensory “triggers”. This may occur via a proposed neural mechanism called Hebbian learning. Through this mechanism, “cells that fire together wire together.” In other words, if two neurons are connected together, then if they both happen to to fire at the same time, their synaptic connections are strengthened.

So to use Proust’s famous example from In Search of Lost Time, let’s say you are eating a piece of cake at teatime in your aunt’s house. A neuron — or group of neurons — linked to the taste of the cake will presumably fire. Let’s call it neuron A. Similarly a neuron that is linked to the sight of your aunt will also fire at the same time — let this be neuron B. Let’s assume that neuron A projects to neuron B. Then according to Hebb’s rule, the strength of the connection between A and B increases. This in turn improves the ability of A to cause B to fire.

The more connections there are, the more opportunities for Hebbian learning. So while you are listening to a lecture or reading a book, connections with other experiences and memories are being made, rendering the information easier to access. Synesthesia may give you more “storage space”, and as a bonus, it may give you more ways of accessing that storage space.

The memory system may be like a labyrinthine mansion. Your memories are locked away in the rooms of this vast maze of a building, and to remember something is to find a way to get to the the room where it is stored. The memory mansion of someone without synesthesia may be full of rooms that each have only a single entrance. Without knowing the way to the right entrance — the right recollection strategy — the memory may be present but inaccessible. The memory system of a synesthete, by contrast, may be like a mansion whose rooms have several entrances, as well as secret passageways linking wings of the building that are usually far apart. So a synesthete may have more ways to navigate the maze of his or her own memory!

This is of course speculation, and careful experimentation and theory will be needed to come up with a more solid explanation!

There are documented cases of synesthesia co-occurring with exceptional memory:

Savant Memory in a Man with Colour Form-Number Synaesthesia and Asperger

Synesthetic Color Experiences Influence Memory

Some more relevant citations:

Savant Memory for Digits in a Case of Synaesthesia and Asperger Syndrome is Related to Hyperactivity in the Lateral Prefrontal Cortex

Do Synesthetes Have a General Advantage in Visual Search and Episodic Memory? A Case for Group Studies

This paper suggests synesthesia may not always confer an advantage. The authors say “The results indicate that synesthesia per se does not seem to lead to a  strong performance advantage. Rather, the superior performance of  synesthetes observed in some case-report studies may be due to  individual differences, to a selection bias or to a strategic use of  synesthesia as a mnemonic.”

So synesthesia may not itself be a memory-enhancing condition, but a basis from which to discover or create improved memory-recovery strategies — a way to build new doors and secret passageways in your memory mansion! 🙂

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