Posted: Dec 31, 2022 1:47 am
Aha! Just as I thought... I don't have an answer! 
The two main proposed areas of explanation I've read are:
i) stem cells which, in the original (?) planaria individual were modified by the chemical environment induced by experiences (i.e the training of light aversion), and the retained modifications impact the structural development of the new brain at the molecular level.
ii) Non-coding RNA's may already be involved in the formation of memory, and the way RNA transcribes DNA is modified by past states which then continue on with those modifications in the new-brained animal. In that way, at a very crude level, this is like a cookie-cutter where the shape presses out more of the same shape, which in this case, is the memory event.
As far as I am aware, no one's solved any of these yet, although they're both molecular level explanations, so might prove to be too reductionist to hope to account for observations. It's also important, I think, to note that while we use the word 'memory' here as a broad category where past events impact future ones, the type of memory that may result from epigenetic factors tend to be ones where stimuli have effected biochemical changes in the body, and that environment may be the key part of the puzzle as it persists - the bridge between the two.
The two main proposed areas of explanation I've read are:
i) stem cells which, in the original (?) planaria individual were modified by the chemical environment induced by experiences (i.e the training of light aversion), and the retained modifications impact the structural development of the new brain at the molecular level.
ii) Non-coding RNA's may already be involved in the formation of memory, and the way RNA transcribes DNA is modified by past states which then continue on with those modifications in the new-brained animal. In that way, at a very crude level, this is like a cookie-cutter where the shape presses out more of the same shape, which in this case, is the memory event.
As far as I am aware, no one's solved any of these yet, although they're both molecular level explanations, so might prove to be too reductionist to hope to account for observations. It's also important, I think, to note that while we use the word 'memory' here as a broad category where past events impact future ones, the type of memory that may result from epigenetic factors tend to be ones where stimuli have effected biochemical changes in the body, and that environment may be the key part of the puzzle as it persists - the bridge between the two.