Tuesday, January 20, 2015

Yet more on intra-neural computation

Milan Rezac sent me these two links (here, here) to articles in Science Daily that many should find interesting.

The first seems to directly support Randy's conjecture about the physical locus of biological memory. More specifically, the reported research from UCLA presents evidence "contradicting the idea that long-term memory is stored at the synapses." David Glanzman, the guy whose whose name comes last in a list of six (does this make him senior author? or last author? or? I never understand the attribution conventions in these bio papers. At any rate, it's his lab) says that the work "suggests that memory is not in the synapses but somewhere else. We think it's the nucleus of the neuron. We haven't proved that though."

The experiment described sounds kind of cute. Like the Hesslow experiment that Randy described, the technology has developed to the point that one can study how neurons learn in a petri dish, at least Aplysia neurons (the victim of choice).  What this experiment did was disrupt and then encourage synaptic connections from growing and then seeing whether when a memory is retained the regrown connections have any evident pattern. The idea being that if memories were retained in the synaptic connections then this would influence the kind of synaptic growth that one sees. Conclusion by Glanzman (and here I quote the report, not G himself): "there was no obvious pattern to which synapses stayed and which disappeared, which implied that memory was not stored in the synapses." In other words, were memories stored in synapses we would expect them to be reflected in systematic patterns in these synapses. But there is no such pattern, yet memories are  retained. Conclusion, they are not retained in the synapses. Note, interestingly, synaptic growth seems correlated to memory. However, it does not appear to be the locus of the memory. What role does it play? The article doesn't say. However, it suggests that a correlation between synaptic growth and memory is insufficient for determining where memories are stored. This is interesting given Lisman's proposed experiment that he proposed during Randy's talk (see here).

The second paper Milan set along should appeal to Evo-Devo fans (this could be a punk rock group, couldn't it?). Here is the abstract:

The fundamental structures underlying learning and memory in the brains of invertebrates as different as a fruit fly and an earthworm are remarkably similar, according to neuroscientists. It turns out that the structure and function of brain centers responsible for learning and memory in a wide range of invertebrate species may possibly share the same fundamental characteristics.

This suggests that the mechanisms underlying learning and memory in even very simple animals are the same as those we have in higher vertebrates. Biologically, this does not strike me as surprising. We have known for a long time that the neuro-chemical and genetic basics are the same in e-coli (and fruit flies, aplysia, slime molds, horse shoe crabs) and humans. Indeed, this is why doing research on the former tell us so much about the latter. That this is also true for mental capacities (memory, learning) should not be much of a surprise. (A little sermon here: though people love to criticize linguists for making general claims based on a small variety of languages (something that, btw, is simply false as any look at the journals will show) the same kind of criticism does not appear to extend to biology where one concludes a lot about general (dare I say universal) biological processes from what happens in e-coli and flies).  At any rate, it seems thnat human brains "share the organizational principles" evident "in arthropods and other invertebrates." The take home message seems to be that biology is very conservative in the mechanisms that it uses. Once a trick is discovered able to do useful biological work (seeing, remembering) this trick is recycled again and again. Taken in conjunction with the observation that unicellular slime molds can store interval information in memory (see here), this suggests that human memory can do so and does do so as well. Randy rules!!

Anyhow, thx Milan for the papers. Lots of fun.

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