Memories — written on your DNA?
How does long-term memory work? It involves many changes in your brain, from changes in how strongly individual neurons talk to each other, to the actual birth of new neurons. But one
fascinating possibility involves the DNA in your neurons!
See those glowing dots? Those are methyl groups
, consisting of a carbon and 3 hydrogens. They can attach to certain locations in your DNA and prevent genes from being expressed. This is called DNA methylation
, and it's important part of the system you use to turn genes on and off.
These methyl groups can even be transmitted from parent to child! For example: if you are hungry for much of your life, your body will adapt, using DNA methylation — and your children can inherit these adaptations
. This will make them more likely to become obese if they get as much food as they want.
All this makes evolution more interesting than people had thought. We can inherit traits our parents acquired during their lives!
Given all this, it's natural to ask: does DNA methylation play a role in memory?
There are hints that the answer is yes
. For example, scientists gave some mice an electric shock and others not. They looked at whether a specific gene in the mice's neurons was methylated. It was more methylated in the shocked mice... and this lasted for at least a month.
What was this gene? It's the gene for a protein called calcineurin
, which is thought to be a 'memory suppressor'. More precisely, calcineurin tends to prevent the neurons from forming stronger connections between each other.
So: the mice responded to an electric shock by attaching methyl groups to their DNA. This reduced the production of calcineurin, which tends to prevent the brain from forming new connections. So, their brains could more easily build new connections.
And all this happened in a specific location of the brain: the anterior cingulate cortex, which is important for rational thinking in humans, and something similar in mice.
This is just one of many experiments people are doing to understand the role of DNA methylation in memory. And DNA methylation is just one of the ways a cell can control which of its genes get expressed! There's a whole subject, called epigenetics
, which studies these control systems.
You could say that epigenetics is a way for cells to learn things
during their lives. When you move to a hot climate, and then your body "gets used to" the heat — sweating less and so on — that's epigenetics at work. So, maybe it's not surprising that epigenetics is also important for how the brain learns things.
Here's a nice article on the role of epigenetics in memory:https://en.wikipedia.org/wiki/Epigenetics_in_learning_and_memory
and here's one about the role of DNA methylation:
• Jeremy J. Day and J. David Sweatt, DNA methylation and memory formation, Nature Neuroscience 13
(2010), 1319–1323. Available for free at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3130618/
The experiment I described is here:
• Courtney A. Miller et al
, Cortical DNA methylation maintains remote memory, Nature Neuroscience 13
(2010), 664–666. Available for free at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3043549/
If you want to learn more about how epigenetics can pass information from one generation to the next, start here:https://en.wikipedia.org/wiki/Transgenerational_epigenetics
A nice quote from Joseph Springer and Dennis Holley's book An Introduction to Zoology
:Lamarck and his ideas were ridiculed and discredited. In a strange twist of fate, Lamarck may have the last laugh. Epigenetics, an emerging field of genetics, has shown that Lamarck may have been at least partially correct all along. It seems that reversible and heritable changes can occur without a change in DNA sequence (genotype) and that such changes may be induced spontaneously or in response to environmental factors — Lamarck's "acquired traits". Determining which observed phenotypes are genetically inherited and which are environmentally induced remains an important and ongoing part of the study of genetics, developmental biology, and medicine.
There's a huge amount of stuff to learn in these areas, and it's pretty intimidating to me, since I'm just getting started, and it will probably never be more than a hobby. But here's some more stuff:
Changes in how strongly individual neurons talk to each other are called synaptic plasticity
These include long-term potentiation
, meaning ways that two neurons can become more strongly connected:https://en.wikipedia.org/wiki/Long-term_potentiation
and also long-term depression
, where they become less
A basic rule of thumb is that "neurons that fire together, wire together". But there's a lot more going on.... #spnetwork
doi:10.1038/nn.2560 #epigenetics #memory