I took Curious Expedition's advice several few weeks ago and went to Obscura, an antique shop in my fair city, to see the antique anatomical model they have lurking in a glass case in the back of the shop. Fun, but as usual with antique shops I never actually find what I think I came into the shop for. My friend and I, I shall call him The Quiet One for the sake of anonymity, found an antique dream symbol encyclopedia which had all sorts of useful information in it such as that if you dream about your abdomen it portends news about your house, or some such nonsense. In any case, I woke up this morning having had a dream about my kidney (one of them) and I wished I had bought the book. Maybe if you dream about your kidney it means you will do well on your Cognitive Neuroscience Final and you can stop studying. OK, maybe not.
Yes, it is finals time. I have one Tuesday and one on Wednesday, hence the dearth of posts on my reading. Reading? What reading. I'm studying 12 hours a day and when I finally get into bed with a book I fall asleep. And then I thought, why I could kills two birds with one stone, I'll write some little neuroscientific tidbits for those of you curious about such things. For example, those of us interested in studying the elusive phenomenon of attention have all sorts of little complications on our hands - besides the fact that no one can exactly say what it is, but we all know it when we see it.
When does attention happen in the brain? There has been a battle raging around the field for years as to whether attention happens early or late (we're talking in miliseconds here folks, that's thousandths of a second). As with most questions about attention, the answer is - it depends. It depends on whether the difficulty of your task is high or low, it depends on whether the response required of you is complementary to is distracting from the behavior you have used to perceive your environment, and it depends on whether you have done it before. Think about how much attention it required to learn to walk down a flight of stairs and think now about not only how little attention it requires but really how distracting it is to think about walking down stairs as you walk down them. But we can actually measure the fact that the brain is paying attention even before it is perceiving. For example, if a cue prepares you for the fact that you will receive information in either visual rather than auditory form, you can see with an fMRI that the brain appears to give more activation to the regions that process visual as opposed to auditory information prior to that information even appearing. There is nothing to see yet but the brain is readying itself to see rather than to hear (Hopfinger et al, 2000).
Other questions attention researchers ask are - when attention selects something what does it select? Is there attention to areas of space? Is there attention to objects within that space? Are those two phenomena or one? And when the brain pays attention does, as Johnny Mercer and Harold Arlen say, accentuate the positive or eliminate the negative? Once again, we can see instances in which it does both. If a monkey focuses the center of his vision on an object, we can measure individual brain cells firing faster that correspond to that area in space he perceives, and in the presence of a distracting object to ignore, we can measure cells corresponding to the area ignored as not only not firing, but actively suppressing their rate of firing.
We have also been reading about the role of sleep in memory, which is dangerously tempting for finals time. I am sure I will do much better on my exams if I could only take little naps between articles. The stages 2, 3 and 4 of Sleep are very active in the consolidation of memories, which is a process that takes what we have learned and makes it less resistant to interference without additional practice. Walker and Stickgold's 2004 article is a pretty comprehensive review of the research. They trace a path through the many studies done in humans and animals, on declarative memory (requiring our awareness) and non-declarative memory.
1. Working with animals on procedural memory - learning a physical task - you can actually observe the patterns of activation seen in the brain during training played out again during REM sleep. Upon waking the amount of improvement is strongly correlated with the amount of reactivation seen.
2. Brain patterns seen in slow-wave sleep seem to rapidly play out that same activity and the waves seen in REM sleep can actually be shown to facilitate physical changes in the hippocampus - a part of the brain important in consolidating memories. This is strengthened by the fact that if you inhibit protein synthesis (which is necessary for those physical changes to take place) you inhibit the learning improvement ordinarily seen on the following day.
3. A genes associated with learning-promoting environments is seen "turned on" during REM sleep, and stimulation of regions of the hippocampus associated with making the physical changes that are our memories also turns on this same gene.
Their article makes a pretty strong argument for the role of sleep in memory by bringing together a large body of research.
In my other class - Neurochemistry/psychopharmacology - what I have found most interesting to learn about is how drugs teach us about disease. Illnesses of the brain are necessarily illnesses of the mind and the body. It is often very difficult to learn about the mechanisms behind them because you have to be very inventive to not simply test people who are already ill. If you test people with a disorder it is hard to know whether you are observing causes of a disease or manifestations of it, or of the medications prescribed to treat it. Much can be learned sometimes through drugs that successfully treat those illnesses. Depression has been one such case. Whether we're looking at Major Depressive Disorder, cyclothymia, reactive depression, or post-partum depression the same medications tend to be effective in treating them for most people. As diverse as these conditions might appear, it seems as though the underlying mechanisms are similar. The actions of some of the major classes of anti-depressants - tricyclics and SSRIs - have been the basis of a lot of research that has unraveled some of the physiological mechanisms in common behind the depressive disorders. As anyone familiar with these meds knows, their anti-depressive actions tend to take two-four weeks to kick in. So these cleverly designed studies looked not just at what happened in the body when someone took at SSRI, which as with any drug is many things, but the time course of these changes. There are literally observable structural changes that distinguish a depressed brain from a treated one. It's fascinating stuff that I'll save for another day.
Sunday, May 18, 2008
Sleep, memory and dreams about kidneys
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