This is a part of the Hot Topic podcast series from the Model Systems Knowledge Translation Center on Changes in Memory After TBI. Dr. David Arciniegas discusses The Neurology of Memory Problems.
So in the – in the period right after an injury, the problem with learning is one where, even though the information is present, even though it's repeated, it doesn't sink in. And so a few minutes after something has been presented, the person might not remember that it had even been discussed. Most of us don't have that experience on a day-to-day basis.
You know? If you present something, you might not remember the details, but at least remember that it was presented. Here, it's as if the tape simply isn't recording. And as a result, a few minutes later, when somebody tries to play back what happened, it's blank. There's no information there to recall.
The process of laying down information, if you will, committing it to tape, takes some days to actually recover, and for people to begin to be able to play back from their own memory a story that makes sense, that isn't filled with gaps or with incomplete information.
So there are a fair number of studies that have looked at the reasons why that learning is difficult. It may be different in the early period after injury than in the late period. So among the reasons in the early period after injury is, first, damage to the structures that we need to pay attention, to, if you will, roll tape and commit things to memory, and then the systems that help retrieve it.
Those include the upper brain stem for the – keeping the lights on and beginning to pay attention, a structure we call the hippocampus, which is important for helping to lay down new memory, and then the frontal lobes, to retrieve that which has already been laid down. In addition to damage to those structures, the early period after brain injury is characterized by a huge output of all kinds of neurotransmitters — the stuff that normally helps the brain function well — are way higher levels than they need to be.
So when I teach our residents, I say, too much of a good thing is not actually good in this circumstance. When you have too much of the neurotransmitters we usually use for attention and memory, they actually take the system down and make it hard to function normally. That — as we call it, the neurotransmitter storm — tends to abate in the first hours to days to weeks after injury with mild or moderate or severe respectively.
Once the storm is over, it appears that some of those neurotransmitters don't simply recover to normal but actually become deficient. In combination with damage to the structures you need for memory, having not enough of the neurotransmitters to help them function is, if you will, kind of a two-hit or a double whammy on those systems we need to actually learn and remember information easily.
So in the late period, the problem is not enough of those chemicals as opposed to, in the early, too much of them to function normally.
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