DR. DUYN: Thank you. We have time for two questions.
DR. MADHAVARAO: In the data, are these -- In the majority of the data or the general data between NAA concentration and cognitive ability, are these subjects preconditioned? In other words, when were the activities subjected to this analysis? They were actually -- they have already taken a test or are preparing for a test?
DR. YEO: Yes, good question. In all of the studies that we have looked at here, the testing was done at more or less the same day as the imaging study was conducted, but the imaging is, of course, separate. They are just resting in the scanner. They are not performing any task while they are in the scanner. But for the normal controls as well as the traumatic brain injury folks, the testing is usually done the same day, but in some cases it is a day before or a day later.
DR. KOLODNY: In view of the studies of Monte de Leone and others showing enlargement of the temporal horn and atrophy of the hippocampus with aging and Alzheimer's Disease, how do you account for the fact that the NAA in the hippocampus apparently in your study does not show a decrease in NAA in aging, unless I have gotten your declaration wrong?
The other unrelated question is: In diffuse axonal injury, it seems to me that NAA measurements would be a very good way of determining the severity of the brain injury.
DR. YEO: In our aging study, I think it is important to note that the regression analysis I reported is across the age span. So we included the younger folks and the older folks, and thus there is a very broad age range there, from the twenties through the seventies.
The studies of aging per se, and especially of incipient dementia, I think, need focus much more -- solely on an older population. So I think our studies pertain more toward normal age changes over the whole adult span than that which might occur just in an elderly sample, which might be more critically significant.
In regard to the latter point, yes, I think indeed that spectroscopic measures of brain injury can add a lot to our clinical understanding. Certainly, Dr. Ross's data attest to that, too, and I can't help but argue that it should be more widespread.
DR. DUYN: Okay. Well, thank you very much, Dr. Yeo.
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