In dna definitely implies in dna sequence. Especially with dna storage becoming a thing, and with aspects of our physiology actually using dna modifications for their function and to "remember" things (e.g. VDJ recombination), its best not to confuse epigenetic vs genetic information storage. Each hypothesis implies different things and different followup questions.

They are certainly different things, but that's why I think more specific language should be used when the difference matters. The other comment was trying to make a more abstract point about what sort of memories an individual neuron can store using DNA, the main point wouldn't really be changed if that was through purely epigenetic mechanisms. I don't think the actual argument he made was compelling, but the claim to be discussed intended a broader definition of "in DNA" IMO. It was focused on the computational implications of the amount of storage a single neuron has.

Perhaps, but I'd argue the differences do matter quite a bit to the computational implications, especially as it relates to ability to reprogram, state space, and persistence, and I think there would be a much different reaction if I made a post mixing up data on a computer's hard drive with the state of whether each transistor in a cpu is on or off, or something like that.

There are different types of epigenetic mechanisms anyway which have different levels of persistence/reprogrammability, so to dive into technical details one would need to get very specific. Different methods for changing the DNA sequence would also have functional differences in how they could store a memory. And it's important to distinguish these mechanisms on a single cell level versus how they function in the body as a whole.

In a single cell I wouldn't call VDJ recombination memory, it's just an efficient way of encoding many different possibilities for types of receptors (and then selecting one). There exist many cells in your body that match a potential antigen you've never seen before - it's just that there are an extremely small number of them. The memory is really encoded by increasing the population of that cell in the body. Which has different storage properties than the individual cell's DNA does. Epigenetic change to a single neuron is unlikely to have a functional effect either, but it is a change that can occur to a mature cell as a reaction to the environment, in a way that VDJ recombination is not. AFAIK there is a lot left to be understood about how epigenetic modifications affect the brain.

I agree this is all interesting and can have implications for computational models, but there are models at many levels of abstraction. So I don't think it is necessary to get at the biological details in order to discuss higher level computational implications. Questions about the capabilities of the memory for each individual neuron would arise, but they could be theorized about without much knowledge of biological details. Of course it depends what your goals are whether you would consider that useful.

Anyway, I think we're both in agreement the OG comment was wrong, I just feel that "in DNA" is very ambiguous, and also not really the problem with his comment given the purpose of HN.