Through the discussions in class and readings, I am confident that the “neurogenesis hypothesis” is really just the tip of the iceberg to unexplored systems and circuits that play a significant role in mental health and illnesses, such as depression, neurodegenerative diseases, seizures, learning, and schizophrenia. I have many thoughts on the current theories and research, however they are quite scattered. So, in an attempt to remain as uncluttered as possible, here’s what I got from the readings:
In relation to neurogenesis and depression, this is what we know:
- Structural changes in the hippocampus, like loss of volume and gray matter, coincide with prolonged major depression.
- Depressed patients exhibit inhibited neurogenesis in the hippocampus , although animal models show that depression can occur without impaired hippocampal neurogenesis and damaged hippocampal neurogenesis does not always lead to depression.
- Animal models of depression are ambiguous and do not necessarily represent human models of depression.
- Anti-depressant drugs or other therapies stimulate hippocampal neurogenesis, with one exception: transcranial magnetic stimulation.
Some limitations with the theories:
- The delay in efficacy of anti-depressants could be explained by brain plasticity, however this hypothesis seems to be fitting assumptions to evidence rather than formulating a theory based on concrete evidence.
- Should researchers be concerned with neurogenesis and the number of newly generated cells, or the type of cell, such as progenitor cells, that is generated? According to Wikipedia (the most reliable source ever), progenitor cells are immature cells with the potential to differentiate or specialize into more specific, “target” cells. Unlike stem cells which replicate indefinitely, progenitor cells divide a limited number of times. Perhaps it is these specialized cells that are the keystone component to the neurogenesis phenomenon.
- What role do the dorsal and ventral hippocampus play in neurogenesis?
On another note, there is one particular overlap with the psychiatric reviews and Solomon’s “Personal History: Anatomy of Melancholy ” that I would like to address. Solomon states that “Some people are disabled by levels of depression that others can handle, and some contrive function despite serious symptoms. Antidepressants help those who help themselves.” But maybe personality is not a factor. Perhaps antidepressants work on those that have a certain level of neurogenesis. In a study highlighted by the Journal of Neuroscience, researchers found that antidepressant behavioral efficacy requires intact neurogenesis. Perhaps it is the individual with too much neuron deterioration in the hippocampus that don’t react to anti-depressants.
Another aspect of depression that I wonder about are the ‘alternative’ treatments. If depression is an evolutionary adaptation of functional systems, then why couldn’t remedies occur in nature? Perhaps herbal medicines, like St. John’s wort; physical activity, from running to yoga; inner healing, like meditation and mindfulness; or even time off from work and unnecessary stress (sabbatical anyone?) should be given a larger portion of the limelight. Or are we turning to the pharmaceutical companies to solve our maladies? Maybe the modern world is waiting for them to conquered the market with the ‘mental illnesses that they export’ (see Daily Show interview with Ethan Waters for more details)?
Solomon states, “it is possible to keep yourself alive without modern technologies, but the price can be high.” Have we come to the point in time where synthetic chemicals are necessary to maintain a stable threshold of emotion? Perhaps the Japanese culture is accurate in their depiction of sadness as “the mildly depressed appear to have more accurate views of themselves, the world, and the future than do normal people. They clearly lack the illusions that normal people promote mental health and buffer them against setbacks.”
On Psychology and Neuroscience 
Great summary, Lia. With your point on personality, anti-depressants, and neurogenesis, maybe some personality traits correlate with a certain level of neurogenesis. That is, maybe people who are more conscientious have a higher level neurogenesis and in turn, they don’t rely on anti-depressants as much to overcome their depressive states…. just a thought!
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I think it all goes back to individual differences. While Solomon definitely has tihngs in there that I can 100% relate to, our experiences are by no means the same. Everyone experiences depression differently–even the intensity of it varies. Why is this? Good question, I wish I knew the answer. What is integral to remember, I think, is that each person is an individual-no 2 people have exactly the same experiences (even in a controlled environment it’s hard to control for differences of experience!).
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Many bits are very much how I too have been thinking about this Lia… it may even be that absolute levels are not nearly as relevant as the capacity in the system. So low levels don’t induce depression nor do high levels mean no depression (is this true?) but rather the capacity to be plastic is the key. ADs may help induce or support plasticity and ng is a consequence of that (mere or not is a matter still being investigated as we discussed in class). I suspect the class on Monday may shed more light on this point. I think the other stuff may work too… it seems clear that it does, in humans and animal models. Jenn’s individual difference are a good point as is the consideration of degree or potency… the notion that sometimes the ADs are needed because things go beyond what can be handled with exercise or vitamins. But getting some ADs in there could get you back to a place where those things (therapy too) can start to work again. Just thoughts :).
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This is such a nice synthesis of points. It really puts into perspective the conflicting evidence that we have to struggle with to understand the role of neurogenisis in depression. I like your point about alternative treatments, and I too wonder if we rely too heavily on medications in modern society. On a different note I also wonder if people use to “self medicate” more for depression. For instance have the instances of alcoholism in depressed patience decreased because of the increase use of antidepressants… not sure, just a though.
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I agree, this is a great way of breaking down and thinking about the articles we have been reading about depression. I think that we have gotten caught up in the thought of the “modern medical world” and we may depend on many medicines to cure us. Maybe we are reversing with the new emphasis on organic and natural foods and that may reflect on our remedies.
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