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emily's picture

Memory, from "Proust Was a Neuroscientist"...a ramble

It is still hard for me to fully grasp how action potentials and synaptic potentials become our reality, our creative ideas, random thoughts, and feelings. I want to share an idea from the book I am reading (for the book review), Proust Was a Neuroscientist by Jonah Lehrer, about memory that relates to what we have learned about with respect to neuronal connections and may help put my question into context and maybe even help me (and others) clarify as I explain it out. 

Lehrer recounts a so-called controversial theory about how our memories endure even when we've forgotten about them, how memories last, from Dr. Kausik Si (former postdoc in lab of Nobel laureate Eric Kandel). Si realized "the mind is in a constant state of reincarnation" so, "our memories must be made of a very strong material, something sturdier even than our cells". But Si also realized that a neuronal memory also had to be specific. As we discussed in class, things like memories and ideas are patterns of activity across inputs or outputs (sensory or motor), so this makes sense in our context: a specific  is a specific pattern of activity. Si then thought about what would mark a specific dendrite branch as a memory, for a specific pattern. To sum up his experiments and thought processes with its conclusion, Si found a prion, a protein that can functionally exist in two states  (active and inactive) and can switch their own states, or, activate themselves. The prion Si found, CPEB, is able to change its shape with ease, "creating or erasing a memory", as neurotransmitters like serotonin and dopamine can change the structure of the protein into its active state. Activated CPEB marks a dendritic branch as a memory. From there, it can "recruit the requisite mRNA needed to maintain long-term remembrance" (mRNA --> protein, and memories need new proteins). Then, a reminder of that memory, like a smell or a taste triggers "a rush of new neurotransmitters to the neurons representing [that memory], and, if a certain tipping point is reached, the activated CPEB infects its neighboring dentrites. From this cellular shudder, the memory is born". Furthermore, because CPEB is a prion, "every time we conjure up our pasts, the branches of our recollections become malleable again. While the prions that mark our memories are virtually immortal, their dendritic details are always being altered...."

So, to conclude, again: memories are specific patterns of neuronal activity. When stimulated, that same neuronal pattern will fire, and become the memory from before in our heads. But, as we are always changing, influenced by our environment, we are always making new neuronal connections, new memories which feed off each other. Our memories are always different each time we recall them because we are always different when we recall them. Action potentials are all-or-nothing, neurons are isolated from each other, but the "empty" spaces between them, the synaptic clefts, allow for different patterns of activity. Our memories "exist as subtle shifts in the strength of synapses", but what about ideas and thoughts-- original, or are they also triggered by past experiences? Are ideas and thoughts merely spontaneous/random outputs from neurons triggering a pattern of neurons? How does this pattern know how to travel? If "random motion" (of ions) causes random outputs, how come our thoughts and ideas are so organized? Is "inhibition" a major key in organization?


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