Friday, December 15, 2006

History in the making - the neurogeneisis discovery

There is an old article by Jonah Lehrer in the Seed magazine regarding the historical process via which the fact of neurogenesis in the humna brain was discovered and established.

One of the findings related to the stress/depression and the-lack-of-neurogenesis linkage and the underlying mechanisms that are involved (including sertonergic triggering of cascade reactions that lead to increase in trophic factors). A corollary finding was that enriched environments also lead to more neurogenesis and can help heal the scars formed due to depression/stress by stimulating neurogenesis in the adult brain. How neurogenesis (in areas like hippocampus and dompaminergic neurons) leads to recovery from depression/ stress is still not clear.

To briefly summarize the findings (though it is highly recommended that you read the original article which is very well written):

  1. Neurogenesis happens in adult brains (rats, primates and even humans).
  2. Stress reduces neurogenesis.
  3. Depression and reduced neurogenesis have been found to co-occur.
  4. Enriched environments lead to increase in neurogeneisis. (in rats, marmoset monkeys)
  5. Sertonin-based antidepressants primarily work by increasing neurogeneisis.

Hence inductively it seems probable that Low IQ is caused by Lower SES. (OK, this may seem like a joke...but do go and read the article and Gould's views on the stress and poverty relationships- and I find her views (and her supporting experimental and observational facts) quite plausible.)

The scientists profiled in the article, at that time, were still wondering (and actively exploring) the exact mechanism between neurogenesis and depression/ stress.

My hypothesis of why depression leads to less nurogenesis in hippocampus would be related to the role of hippocampus in memory and learning and how, for example, repeated exposure to shocks in rats leads the rats to exhibit a phenomenon known as 'learned helplessness'. Once the memory of a shockful and distressing repetitive experience is entrenched in the rat's memory, in the hippocampal region, she may not try to explore the environment that much, to discover and learn what has changed regarding the environment, and whether the stressful conditions and environments are over. This may lead to reduced neurogenesis as the rat's brain resigns itself to fate. This inability-to-learn or 'learning helplessness' (my slightly changed term for the same behavioral description) may lead to a vicious downward cycle leading to depression.

Once the neurogenesis is re-triggered, either due to administration of prozac or other antidepressants, or due to Cognitive behavioral therapy (and it had been found using brain scans that these two approaches seem to converge- one working in a top-down fashion (expecations and beliefs), while the other on a molecular and bottom-down fashion ), then the increased neurogenesis leads to an enhanced ability to learn and adapt and thus overcome the depressive epsiode and get rid of the symptoms. In both cases, the brunt of effort to get out of depression is still borne by the individual who is affected.

The other piece of information that caught my fancy was that of the dopimenergic neurogenesis and the potential cure of parkinson's disease based on targetting this pathway. Whether neurogenisis is limited to hippocampal regions, or also happens in the substatntia nigra/ VTA region (where I guess all the dopaminergic neurons reside) is an important question and my lead to more insight as to which all areas of the brain (or all areas) are susceptible to neurogenesis.

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AlvaroF said...

Hi Sandy, I don't know the specific mechanics in detail, but let me borrow from Robert Sapolsky and say that, if the zebra is about to be attacked by a lion, the only priority until she is safe is to focus all energies on running, and reacing safety. She couldn't care less for neurogenesis, or digestive processes, that may have a long-term benefit.

The problem with humans is that we trigger that same reaction too often, including when there are no real lions out there-except in our very real imagination.

Conclusion: stress management is a key brain fitness need, on par with brain exercise/ mental stimulation. Another alternative, I guess, would be to somehow transform ourselves into lions :-)

Sandy G said...

Alvaro, you are right!

One needs not only stress management (protection from external lions) but also CBT in case of depression (protection from internalized/ imaginative lions), otherwise all the cognitive simulation and exercise may be ineffective and may not aid learning and fitness by stimulating neurogenesis. Worse, the zebra may get the ulcers , mediated by say neuronal atrophy and manifested in the form of burnouts , suicidal ideation etc.

Yet I believe it is important to address the external lions()stress) and the internalised lions(depression) separately, and only once one has taken care of these use cognitive fitness programs to garner maximal benefits from neurogenesis or associated mechanisms.

Maybe Sharpbrains can look into including a refresher course in stress-management/ CBT along with its cognitive fitness programs so that even stressed/depressed zebras/elephants:-) are able to reap the benefits.

AlvaroF said...

We sadly have no data for zebras/elephants, only for highly evolved gorillas...

Yes, stress may be external or internal, but our physiological reaction to both is the same, and our emotional self-regulation programs may be the same. We call our field "brain fitness" (instead of "cognitive fitness") precisely to be able to offer programs such as our stress management one...I respect CBT very much, but given that we are focusing on healthy highly evolved gorillas who may not have the time, money or inclination to do CBT, we offer the technology-based solution. Which may be very complementary to CBT, btw.

Just came across a great paper on
"Heart rate variability as an index of regulated emotional responding"

HRV is what the program we offer, called Freeze-Framer (the one you mentioned when we blogged about the Technology & Learning article on us), measures.

Happy holidays!