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SITE: BRAIN BASICS: Know your brain‘
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Es = Extroverts  // Is = Introverts

FACTORS: As already indicated in previous posts, no one is totally one extreme of the other.
However, there are very real biological differences between the brains of Introverted & Extroverted people. Advances in neuro-chemical research show they are more than just psychologists’ observations, but rather rooted in science. Several physiological components contribute to the overall variants.

1. The ARFS : In 1967 Hans Eysenck suggested that the disparity depends on our Ascending Reticular Formation System (ARFS) at the top of the brain stem. It connects the major nerves of the spinal column to the brain – sorting out millions of stimuli coming in every second – letting in the vital ones through, to alert the processing mind.

It’s purpose is to insure the brain receives an optimal amount of stimulation to be happy – at all times. We regulate that system by socializing. Too little & we’re bored, too much & we’re overwhelmed. Is already have a fairly high level of brain-stimulation, so it doesn’t take as much external activity to be satisfied. Es start out with a lower level of stimulation, so need a lot more social interaction to feel good.

So, behavioral differences between Es & Is are due to predispositions in cortical arousal – the speed & amount of the brain’s activity. External circumstances together with these predispositions determine how a person responds to their experiences.

In Es the ARFS is ‘tight’, (Low arousal) making them less reactive to events, making them crave more input. (More….)
For Is the ARFS is wide open & so processes more incoming info per second (High arousal). Their risk is getting too much input, which drains them. EXP: Is are more likely to have ADHD because of a higher sedation threshold. 

Interesting: Some consider the ARFS the gateway to consciousness – an awareness of Self & one’s environment. If we mentally form a clear intention about something we want (specific goal, dream, need….), it is automatically programmed to filter for it!  BUT, damage to it from long-term over-stimulation (constant trauma) causes PTSD.

2. BRAIN QUADRANTS: The specialization differences between Front (Cerebral mode) & Back (Limbic mode) is much more pronounced than the differences between the Left & Right. Most of the areas that initiate action & speech are in the front, while the back gathers & processes data. (More def…) (4 Types def…)

Left & Right quads control different aspects of thought & action:
• L1 = Working memory. Rational Self: analytical, defining, factual, prioritizing
• L2 = Participation. Safekeeping self: experiencing, detailed, maintaining, organized, structural

• R1 = Assimilation. Experimental self: conceptual, envisioning, interpreting, strategic & unorthodox
• R2 = Motivation. Feeling self: harmonizing, interpersonal, relating, sensitive, social.

3. BLOOD FLOW – Front vs Back
Blood flow to any area of the body indicates its activation. A 1999 study focused on the differences between Es & Is, done by carefully measuring the cerebral blood flow in both groups, using PET scans. It found that:

• Introverts have more blood flow to their frontal lobes & anterior thalamus – causing more neuronal activity – than Es – the front of their brain highly stimulated by solitary activities – encouraging an inward focus.
Also, their premotor cortex absorbs external stimuli more quickly – more info coming in faster can flood the brain if not regularly processed. This may explain why Is need more private reflection-time, to analyze ideas & think things through.

• Extroverts get more blood flow to their temporal lobes, posterior (rear) thalamus & anterior (front) cingulate gyrus – mainly back of brain areas involved with interpreting sensory data, giving them an outward focus.

Interesting: A 2012 study of the prefrontal cortex (Fp), a highly complex brain region associated with abstract thought & decision-making, found that:
• People who identify as Is tend to have larger & thicker gray matter in certain areas of the Fp, possibly because they devote more neural resources to abstract pondering.
• Es tend to have thinner gray matter in those same Fp areas, perhaps because they prefer to live in the moment (so they exercise other parts of the brain more).

NOTE: This is NOT a measure of intelligence but rather an indication of usage. Like our muscles, the more a body part is used the bigger it gets.

NEXT: E & I brains #2