Monday, February 18, 2013

New research on how early life experience shapes the brain may be a compelling case for compassion

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Heather Price

In our society, we have a proclivity for believing that an individual has a large measure of control over their circumstances, and that if a person only sets their mind to it, they can overcome a rough start to life. Recent studies are showing just how deep and long-lasting the effects of early life can be, however, and indicate that disadvantaged children can add their own brains to the list of lifelong obstacles to overcome.

Until the 1990’s, the dogma in neurobiology was that adults could not develop new brain cells.  In the past several decades that view has been completely overturned, however, and it is now considered common knowledge that neurogenesis continues throughout an individual’s lifetime.  The critical importance of this process continues to be revealed as studies elucidate its connection with more and more aspects of mental and physical well-being.  A decrease in the brain's ability to form new neurons has been shown to negatively affect learning and memory, and has been linked to such diseases as depression, schizophrenia, and alzheimer's. 

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While there are certain lifestyle choices a person can make to enhance their brain’s ability to grow new cells (such as exercise, avoidance of drug and alcohol abuse, cognitive stimulation, and social interaction), a growing body of research suggests that a person’s lifelong ability to create new neurons is actually laid down long before they have any control in the matter.  In addition to genetic predisposition, circumstances during the first few   months of life, and even while still in utero, have been shown to have significant effects on the brain’s capacity for neurogenesis throughout a lifetime.

In a study published in Nature Neuroscience in 2004, adult rats who experienced prolonged separation from their mothers during the first few weeks of life had significantly reduced levels of cell proliferation and immature neuron production in the dentate gyrus of the hippocampus.  Another study, conducted in 2011, revealed that mice that experienced repeated and unpredictable separation from their mothers during the first two weeks of life not only had reduced numbers of new neurons as adults, but also had less dendrites on those neurons.  

The mechanism for this reduction in neurogenesis is at least partially controlled via hormonal pathways.  Cortisol, a steroid hormone released in response to stress, triggers the release of glucocorticoids, which eventually lead to the atrophying of dendrites, as well as apoptosis (cell death) of progenitor cells that turn into neurons.  Not only does this have a negative effect on young brains during exposure to adverse conditions, but prolonged exposure to cortisol can cause permanent hypersensitivity to glucocorticoids.  In other words, the brain will more readily shut off the production of new neurons when exposed to stressful situations later in life.These long-term effects can impact the actual structure of the brain as well, and have been linked to reduced amounts of both gray and white matter.
White matter consists of myelinated (fat-insulated) axons of neurons, which transmit signals between regions of gray matter, which consists of the cell bodies and dendrites of neurons.  Changes in the amount of gray matter can be directly linked to neurogenesis, while a change in the amount of white matter is related to the reorganization of axons, and formation of new myelin.

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Just last year, the Proceedings of the National Academy of Sciences (PNAS) published a study that investigated the amount of gray and white matter in the brains of children exposed to different early-life conditions. Researchers ran MRIs and EEGs on the brains of three groups of Romanian children: 1) those that had been in orphanages their entire lives, 2) those that had been in an orphanage but were then taken into foster care, and 3) those that had lived with their biological parents since birth.  They found that children raised by their parents had significantly higher levels of gray matter than children who had been institutionalized.  These findings seem to provide a very grim prognosis for children who already have a myriad of obstacles to overcome. There was somewhat of a silver lining in the findings, however, in that children who had transitioned into foster care, as well as those raised by their parents, had significantly higher levels of white matter than children who were still living in orphanages.  This suggests that new neuronal activity can be stimulated in children once they have been placed in a more caring environment, and that perhaps some of the damaging effects of spending early life in an institution can be ameliorated.  

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More research is certainly needed into methods of assuaging the adverse effects of childhood neglect and trauma. In the meantime, these studies have reemphasized the importance of prevention, which in this case takes the form of something humans have known about for thousands of years: loving and attentive parenting.

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While the answer to this problem seems simple, it is something that clearly does not exist as a reality for millions of people who were not born into ideal circumstances. In a culture obsessed with the idea of an individual rising above adversity, most of us would like to think that with a little bit of hard work and a “can-do” attitude, anything can be achieved. While this viewpoint has its merits, it can also cause us to be very judgmental of those in tough circumstances. The growing body of research that is elucidating the connection between early life experience and lifelong brain function may force us to reevaluate our view of others, and will hopefully compel us towards compassion.

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Gould, E. B. McEwen, P. Tanapat, L. Galea, and E. Fuchs. 1997. Neurogenesis in the Dentate Gyrus of the Adult Tree Shrew Is Regulated by Psychosocial Stress and NMDA Receptor Activation. The Journal of Neuroscience. 17(7):2492–2498.

Leslie, A., K. Akers, A. Krakowski, S. Stone, M. Sakaguchi, M. Arruda-Carvalho, and P. Frankland. 2011. Impact of early adverse experience on complexity of adult-generated neurons. Translational Psychiatry. 11: 2158-3188.

Mirescu, C., J. Peters and E. Gould. 2004. Early life experience alters response of adult neurogenesis to stress. Nature Neuroscience. 7(8): 841-846.

Sheridan, M., N. Fox, C. Zeanahe, K. McLaughlin, and C. Nelson. 2012. Variation in neural development as a result of exposure to institutionalization early in childhood. Proceedings of the National Academy of Sciences.

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