There's a lot that I want to say about The New York Times Magazine's special issue, "All in Our Minds," which focuses on a lot of really interesting health-related issues as they are now being studied in neuroscience. While this is literally a treasure trove of neuroscience research there is one commonality, or perhaps theme, that seems to run through most of the articles in April 22, 2012's issue: namely, the importance of the hippocampus in damn near all of our mental functions!
In the article, "How Exercise Could Lead to a Better Brain," Reynolds examines some recent research on mice that examines the role of exercise in their ability to form new neurons. A number of studies have come out that suggest that mice running on the wheel "appears to build a brain that resists physical shrinkage and enhance cognitive flexibility" (1). For mice, all of the shiny interesting toys, colorful houses, and gourmet food do little in comparison to simply running on an exercise wheel. The mice who had an un-enriched environment performed just as well on mental tasks as those who had all the snazzy toys and food, so long as the commonality between the two groups was that they both had access to a wheel and used it. The argument that neuroscientists are making is that exercise ". . . Slow[s] or reverse[s] the brain’s physical decay, much as it does with muscles" (1). And a healthy hippocampus is an important part of countering that decay.
Apparently, and this sort of frightened me as I am getting to the place where this begins to happen, in our late 20's the hippocampus starts to lose 1% of its volume ANNUALLY. As most of you probably know, because I am obsessed with memory and talk about it a lot, the hippocampus is implicated in memory functions and certain types of learning. The loss of volume and health in this structure suggests that learning becomes much more difficult as we age, and, it might come as no surprise, our memory suffers as well. Of course these two things are interconnected and apparently exercise can counteract the loss of volume so much so that if you start walking even in your 60's you might stand to shave a year or two of age off of the brain. This is exciting for many of us because dementia and Alzheimer's disease tend to loom large in our minds--the fear of losing our memories, our autonomy, and eventually our sense of self, is frightening indeed--so start exercising because that can lend healthy and volume to the hippocampus, which will in turn allow your brain to create "lively" neurons and new neuronal pathways (something previously thought impossible outside of childhood), which will allow you to multi-task and for the brain to "strengthen [its] cells and axons, fortif[y] the connections among neurons and spark neurogenesis" (1).
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"Post Prozac Nation" is yet another article in this issue that focuses on the important role that the hippocampus plays in our lives, namely in our emotional health. According to this article the treatment of depression is really quite more nuanced and complicated than serotonin imbalances. A number of research studies have concluded that administering Prozac to
sub-sets of people with depression often yields few results; it is only
in the case of people with severe (not even moderate) depression that
Prozac helps. Studies have given contradictory evidence for whether depression comes from too little serotonin, too much, or something else and now scientists are asking more nuanced questions such as, "might depression have multiple subtypes — some inherently
responsive to treatment with serotonin-enhancing drugs and some
inherently resistant?"
While serotonin is involved with depression, neuroscientists are turning to one of the parts of the brain that is connected to the parts of the brain that regular emotions, the hippocampus and its ability to form new never cells. Although, for a long time neuroscientists thought that the brain couldn't form new neurons; however they are finding out (through their work on mice, which hearkens back to the article on exercise) that "two very specific parts of the brain: in the olfactory bulb, where
smells are registered, and in the hippocampus, a curl of tissue that
controls memories and is functionally linked to parts of the brain that
regulate emotion (5). So, while the hippocampus is able to form new nerve cells, and it is connected to the subcallosal cingulate, which regulates our mood, in a depressed person it is possible that the hippocampus is not forming new nerve cells, which, in turn, means that it doesn't form new connections to our emotional regulator, as Siddhartha Mukherjee describes it: "In the depressed brain, nerve death in the hippocampus disrupts these
signals — with some turned off and others turned on — and they are
ultimately registered consciously as grief and anxiety" (6).
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So there are a number of comparisons that I can draw between the article on exercise and hippocampus health and depression and cell death, the most obviously of which is that the hippocampus' ability to form new nerve cells places it in the unique position to be "manipulated" by us in a positive way throughout our lifetime. That exercise contributes to hippocampus health and neurogenesis well into our lives also has another implication, which is that through positive behavior (exercise) we can encourage cell growth, which, in turn, can promote emotional health. This is because the hippocampus forms connections with the subcallosal cingulate which helps to regulate our emotions--more nerve cells means more connections which means more direct discourse between these parts of the brain. Pretty soon, if it is not already happening, I am sure the connections between all of these pieces will lend themselves to showing how exercise can help us to "re-wire" our emotional brain.
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