NOTICE: Posting schedule is irregular. I hope to get back to a regular schedule as the day-job allows.

Tuesday, May 24, 2011

It's got... Personality! [Full link to blog for email clients.][FT:C44]

This blog, and the series to immediately follow, are really about psychology.  Psychology studies the mind more so than the brain.  Since I am a neuroscientist and not a psychologist, I will keep the speculation to a minumum and just talk about what we (as neuroscientists) know about the brain areas serving these functions.

To foreshadow the coming posts, we have personality, sense of identity, thought vs. intelligence, consciousness and sentience. These subjects take on more of a metaphysical nature because it is difficult to point to a neuron and specify that the activity is part of a "thought." On the contrary, it is relatively easy to identify neural activity associated with a specific sensory input or motor output. 

Most of what we know about "personality," for instance, comes for examining how a person's personality changes after damage to the brain.  Here again, though, we need to be able to separate the psychological (changes due to the patient's personal motivation to make a change) from the physical (changes due to actual brain structure effects).

The most prominent example of personality, and the supposition that the Frontal Lobe controls personality, comes from the case of Phineas Gage.  Gage was a railroad foreman in the early 19th century.  An equipment explosion sent a 3-foot iron rod sailing, and Gage was in its path.  Several reconstructions of the result are at the right.  Miraculously, Gage survived.  He lost an eye, but motor function and memory seemed intact.  However, over time, the friendly, outgoing, dependable Gage became angry, bitter, foul-mouthed and unreliable.

Clearly a personality change, and it was definitely associated with Frontal Lobe (and more specifically, prefrontal) damage.  A fascinating description and picture are here:   

With the perspective of nearly two centuries, we now know that there are many "centers" of personality in the brain.  Prefrontal and upper Parietal Lobe are key areas, although this study claims there are some key differences in size of brain areas:  It should be noted, however, that we should not be quick to specify cause and effect.  We have learned that the brain is highly plastic: persons with brain injury can regain some or nearly all function over time with effort.  Thus it cannot be conclusively stated whether the enlarged brain areas cause the behavior, or are the result of increased activity because of the behavior. 

We also know that personality is also dependent on neurochemicals.  The classic "manic-depressive" state (more appropriately "Bipolar Affective Disorder") results in patients alternating between extremes of extroversion to introversion, friendly to angry, compulsive to lethargic.  In common understanding, this would be considered a personality change, and when on appropriate medication, the baseline personality is somewhere in the middle between the extremes. The change in personality is frequently associated with the balance between activity of neurons that utilize different neurotransmitters:  Serotonin is most important, but norepinephrine, dopamine and acetylcholine are also involved.  Frequently the location of these neurons is in the basal ganglia and midbrain.  Likewise, fear and anxiety are frequently associated with activity in the limbic system (although not exclusively), so the Frontal and Parietal Lobes are not the sole source of neural activity underlying personality. 

As with so many other functions of the brain, personality likely results from interaction with many different brain areas.  There are many similar conclusions when dealing with the "psychology" topics, thus the separate sciences of neuroscience/neurology and psychology/psychiatry which deal with the physical vs. mental aspects of an increasingly mysterious brain!

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