Neurons Constantly Alter Their DNA (2015) | Hacker News Reader

Neurons Constantly Alter Their DNA (2015)

hopkinsmedicine.org

136 pointsgivan28 comments

The use of "rewrite" is a bit misleading- what's being altered in this mechanism is an epigenetic tag that sits "on top" of one of the standard DNA bases; that an individual's epigenetics are altered as they go through life is well known. But since the underlying cytosine is (as far as we know) irrevocably bound to this tag, it has to be replaced by a different (but identical) cytosine. Its more like going over your handwriting to hide an errant punctuation mark than "rewriting."

Actually, it's been a thing for a while that we know the brain has somatic mutations which cause the DNA to differ from cell to cell. While the epigenetic tags are also affected, it goes beyond attaching tags. The brain literally rewrites its own DNA.

https://www.genomeweb.com/sequencing-technology/single-neuro...

Acquiring somatic mutations is not "rewriting its own DNA", it's just acquiring mutations. You can't replicate a piece of DNA without the chance of a mutation happening. The error rate in humans is about 1e-9 mutations/base, so by the time you've grown a brain you're likely to have a whole bunch of somatic mutations just by chance.

Better link without paywall and with link to actual article

http://neurosciencenews.com/neuron-lineage-genetics-2792/

To me, it sounds more like surgically replacing a fragment of your skin to get rid of a tattoo, then after some time replacing it back again to reapply the tattoo. So not exactly a walk in the park. The article seems to explicitly state that it's quite a fragile and risky operation, and that's actually why it so surprised the scientists:

"[T]he process involves making a cut into DNA, it leaves the DNA somewhat vulnerable to mutations, so most cells use the process sparingly [... Studies suggest that in] mammals' brains [it happens] more than in any other area of the body — and Song’s group wanted to know why all this risky business was going on in such a vulnerable tissue as the brain."

I am not in that field, but have researched into methylation a bit. The way I understood it, is that methylation groups are applied to genes that are to be "muted". Thus, if there are not enough methylation groups available, genes that should not be expressed, are.

Some form of memory storage. Maybe rewiring the firing mechanism based on some input.

Ok, we'll s/rewrite/alter/ the title above.

Very appropriate.

also 2015

Good catch. Added.

This is a bit silly, eh. Every cell in your body does this kind of epigenetic modification, there are a whole host of factors whose only job is to methylate DNA. Furthermore, this is not really "altering DNA", the sequence doesn't change, this is just a way to mask gene expression - if you methylate cytosines near the promoter region of a gene, RNA polymerase has a harder time sitting down and transcribing the gene, reducing its expression.

Neurons do this, germ cells do this, immune cells do this, every cell in the body does this.

What's interesting here is the specific factor (Tet3), not the occurrence of epigenetic modification. The perils of science journalism, as usual.

Exactly. I should know better and I got caught up in the excitement of "neurons editing their DNA". The Hopkins press release department was either clueless or trying to make this paper sexier than necessary. The Tet3 finding is cool; Wonder if that factor does the same thing in other cells besides neurons, or if really just responds to synaptic activity.

Many years ago I attended a talk by Bernard Widrow (discovered/invented a precursor to the backpropagation algorithm; i.e. the least mean squares filter) [1]. He believed that long-term memories are stored in DNA [2]. At the time, I and others thought he was completely wrong.

Maybe it is not such a crazy idea. Code is data, after all (especially if our brains are written in LISP).

[1] https://en.wikipedia.org/wiki/Bernard_Widrow [2] https://web.stanford.edu/class/ee373b/cognitive_memory2.pdf

I knew it - our brains are written in Lisp!

http://www.pgc.com/pgc/home-stuff/papers-archive/think-w-dia...

This is a pretty cool thing for electric amoeba colonies in skull aquariums to be messing around with.

I'd wager white blood cells are a species apart, in this territory.

Is this the mechanism responible?

http://discovermagazine.com/2013/may/13-grandmas-experiences...

Is the word 'toggle' being used correctly in that article? Do they mean 'modulate' maybe? (If they're talking about a continuum, rather than a "one or the other" polarity.)

If this is the case, then we have an intersting problem. Epigenetics change, DNA - due to mutations can differ from cell to cell, people get injected with completely different DNA in the case of organ transplant. New neural pathways are created. Cells in the body are changed constantly. Memories are changed. Things like height, weight, personality traits, name, disorders, spatial location etc. can all be changed as well.

So, this raises the question of whether someone can seriously say: "I did something 15 years ago" - when many of the things that make up the human have been changed plus the person saying it is most likely making up a story about past(confabulation). What do you think?

“No man ever steps in the same river twice, for it's not the same river and he's not the same man.” -Heraclitus (supposedly)

int a = 0; a = 1;

Same variable, but the value stored changes over time.

Consider the human body to be like a variable. The value stored changes over time. When we use "I" in the present, we are talking about the "value" stored in our body in the present. When we use "I" in the past, we are talking about the value that was stored at a different time. That is how we can refer to systems that change over time using the same identifier - by treating them the same way we treat variables.

All cells do this. It's much closer to RAM than ROM. Also, memory's are structural and much larger features than this stuff.

> So, this raises the question of whether someone can seriously say: "I did something 15 years ago"

Only if you define "I" as something that doesn't match reality, just because people change doesn't mean they aren't still themselves. "I" doesn't refer to some ethereal unchanging thing, it merely refers to the self which is ever changing.

I think the self is "renewed" or "reconstructed" every moment. Life is a chain of these self-moments. There is nothing linking these self-moments other than shared past experience. No "personality" essence is preserved. Personality emerges every moment anew, based on the current factors, just like consciousness and other mental processes. We don't live for 80 years, we live for a few moments, but a chain of Self instances exists for 80 or so years. We die constantly throughout our lives.

I see the self like the emergence of a car wave on the highway. The wave appears spontaneously when the highway is crowded. It can disappear on its own when the density decreases a little. It exists moment by moment as a result of emerging processes and underlying conditions. It is in a constant state of flux. A great part of it is dependent on the external conditions, not just the cars.

Similarly, external factors are also part of the momentary self. The self is not separated from the external world, but the world plays a part in it. It selects the momentary self from a complex space of possible personalities. Basically, we are the resultant of the stream of experiences and conditions that existed around us all our life. We know that also from artificial neural networks, which are built by distilling their experiences.

[removed]

Questions already well explored by philosophy; nothing in the article raises any new questions about the nature of self.

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