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.”