Habits: Stress and the brain

Habits


Man, it has been said, is a creature of habit.  We learn to do things in a certain way, and by repeating our actions, we develop a sense of comfort and satisfaction in their doing.  This is certainly true of behaviors, but it is equally true of thoughts and feelings.  Since thoughts and feelings begin with brain activity in the prefrontal and


The front of the brain is comprised of the frontal cortex and the pre-frontal cortex.  This is the central command area from which we do our thinking, generate ideas, initiate actions, build up (and exercise) our personal will.  It is sometimes referred to as our ‘thinking brain.’  The pre-frontal cortex is larger in humans than in any other animal, comprising about 30% of our total brain mass, and this is primarily what distinguishes us as a species.  The pre-frontal cortex in Chimpanzees, by comparison, makes up approximately 12% of their total brain mass, and in dogs it makes up approximately 5%.  


Behind and deep to the pre-frontal cortex is an area called the cingulate gyrus.  Shaped like the Nike ‘swoosh’ turned upside down, the cingulate gyrus is responsible for flexibility of mind, the ability to shift from one thought to the next, to make comparisons, to multi-task; to mentally shift gears, as it were.  The cingulate is sometimes referred to as the ‘flexibility brain.’


Finally, deep to the cingulate gyrus lies the limbic system.  As described above, this small, very deep area is the center of emotion.  It is also the storage center for long term memory.  Fear, love, reproductive drives, and the physiological processes that mediate those and many other emotional experiences are generated here.  The limbic system is sometimes referred to as the ‘emotional brain.’  


FMRI (functional magnetic resonance imaging) is providing new, fascinating data about the brain.  FMRI measures blood flow.  Since more blood is needed when we are actually using an area of the brain, blood flow is an indicator of brain activity.  Because we have known for some time that different areas of the brain have different functions, there was a long held assumption that normal brain activity should show selective areas of activation and quiet at any given time.  For example, it would make sense to predict that while your are doing math, the pre-frontal cortex, or ‘thinking brain,’ should be active, while the cingulate gyrus and limbic system should stay, relatively speaking, more quiet.  Similarly, we might expect that while experiencing rage or fear, the ‘emotional brain’ would light up with activity while the ‘thinking’ and ‘flexibility brains’ would be dimmed.  


In fact, FMRI has shown something very different.  Rather than patterns of selective areas of activation and deactivation, what FMRI has shown is that healthy brains demonstrate a pattern of more generalized activation, with virtually the entire brain lighting up or quieting down as one functionally integrated organ.  In a healthy brain, we may see slightly more or less activity in a particular area depending on what type of activity the brain is primarily engaged in at any given moment, but there is generalized activation of the pre-frontal, cingulate, and limbic areas whenever the brain is engaged to do anything!  In healthy people, all three brains act together.  


This is not to say that we never see selective areas of activation and deactivation.  We do see it–too often in fact–just not in healthy brains.  The brains of drug addicts, alcoholics, patients who have sustained brain injuries, patients with major depression, or other psychiatric conditions, show hot and cold spots, giving a ‘Swiss cheese” like appearance on FMRI.  Even more interesting, is that patients with chronic pain but without any identified disease or history of injury show this same pattern, as do people who are under chronic stress.