Wednesday, April 26, 2006

Memory Consolidation III (the thrilling conclusion)

Hi America.

I was just rambling on about some research I've been reading about and I yammered on a bit about memory consolidation and how that refers to the process of converting short term memory into long term memory, and how this is dependent on proper functioning of a brain area called the hippocampus. And then I went on to describe some recent data that shows how the hippocampus might be recording the events of the day and playing them back so that you have many opportunities to store them in long term memory. I'm doing this because it's my blog and I'll put here whatever I want to.

Dave had a good point about how it relates to Alzheimer's Disease, and yes, people with AD do have structural abnormalities in their hippocampus, with very dense neurofibrillary tangles and ß-amyloid plaques in thier hippocampus (those two things are indiciative of AD). There is even a report of 20% or greater tissue degeneration in the hippocampus of patients with mild-moderate AD. And regarding the affect of stress, here's a great example showing how stress affects learning. Initially it seems to help, where stressed rats make fewer errors on their maze, but continued stress hurts their performance dramatically - many biochemical changes can be affected by the stress hormone cortisol.

Anywho, back to the memory consolidation, there's some brand new data that changes things a bit. The idea was nice and clear, that the hippocampus can drive cells in the proper sequence and they will then be strongly connected to each other and things will remain that way, burned into your mind for all time, but it's not so cut and dry. Apparently neurobiology is somewhat complicated. Who knew? Anyway, yesterday I talked about how, if you record which cells are firing and the order they fire, and then look at the order they fire in the sharp wave during sleep, you see that it's the same order, and it's sped up which would make it more likely to change the wiring of cells in cortex, but if you look at what's happening directly after the animal runs the maze, you see the same kind of group firing - and a similar sharp wave. But if you look at what order they are firing during that sharp wave, you find that it's sped up, but it's reversed. It's different than random, and it's the opposite of what was happening just a few seconds prior.

And if you think in the same simple way that this is driving cells in cortex to form connections between them, it's strange, because this order of firing would actually serve to weaken the connections between them. Who knows why. Maybe for some reason you want them weakened. On some level, there may not be any real difference in a system that learns by strengthening specific synapses and a system that learns by weakening specific synapses - on some level. Or in another way, firing the cells in reverse order would actually strengthen the synapses in the reverse order (i.e. the connections from cells C -> B -> A are stronger, and the connections from A -> B -> C are made weaker) and maybe that is beneficial in some way. I don't know how it works, I'm open to your ideas.

That's enough science for now.

Keith out.

Oh, yeah, 4 miles this morning - nice and cool, you should have come running with me, America. Maybe tomorrow, on the bridge - we leave from the parking lot of Ichibon's on the Kemah side of the bridge at 5AM sharp.


Jill said...

Mind blowing!!

atownrunner said...

Have you been forgetting to blog?