Neurodiversity Part 3:
Research on Blood Flow In The Brain

As mentioned in Part 2, human behavior research into introversion and extroversion does not align with the public view of these terms. It isn't culled down to how shy or outgoing a person is. And the research dating back to brain scans in the 1960's and 70's shows similarities to the public definition of neurodiversity (coined in the 1990's by Judy Singer.)

In Part 3, we'll be looking at research on blood flow in the brain. Then we'll go over research into cortical arousal, anticipation, and behavioral systems in subsequent parts.

Also, here is a link to the seven executive functions listed in a Psychology Today article for reference.

Blood Flow In The Brain
In a study by Johnson et al in 1999, the authors noted that “introversion was correlated with blood flow in the lateral extent of the frontal cortex, Broca’s area, the insular cortex, the right temporal cortex, and the anterior nucleus of the thalamus.” The areas correlated with more blood flow for extroverts were the anterior cingulate gyrus, right insular cortex, bilateral temporal lobes, and pulvinar nucleus of the thalamus. 

With the insular area, the authors mentioned that “blood flow in the anterior insula is correlated with introversion, whereas blood flow in the posterior insula is correlated with extraversion.” (Source)

Here are the regions and their primary tasks, based on publicly available research. Quite a few of the sources I looked at still mentioned that the interconnectivity of these regions may be relatively unknown or not well understood — including regions like the insular cortex.

Introversion & Areas of Blood Flow:

  • Lateral extent of the frontal cortex - Per the aforementioned study: “Activity in these frontal regions is thought to mediate memory retrieval and planning, reflecting the inward focus of cognitive processes in introverts.” (Source)
  • Broca’s area - “Different regions of the Broca area specialize in various aspects of comprehension. The anterior portion helps with semantics, or the meaning of words, while the posterior is associated with phonology or how words sound. Broca area is also necessary for language repetition, gesture production, sentence grammar, and fluidity and is involved in interpreting others' actions.” (Source); “The axial view shows an activation in Broca’s area that likely reflects “self-talk” on the part of introverted individuals.” (Source)
  • Anterior insular - “Cytoarchitectonically complex and richly connected structure that functions as a cortical hub involved in interoception, multimodal sensory processing, autonomic control, perceptual self-awareness, and emotional guidance of social behavior.” (Source); “Recent studies of emotion have found that the anterior portion of the insula is activated when subjects recall or imagine events, whereas the posterior insula is activated by interpretation of current sensory information (49, 50).” (Source)
  • Right temporal cortex - If nondominant, “involved in learning and remembering non-verbal information (e.g. visuo-spatial material and music.)” (Source)
  • Anterior nucleus of the thalamus - “A key component of the hippocampal system for episodic memory.” (Source)

Extroversion & Regions with More Blood Flow:

  • Anterior cingulate gyrus - “It is thought that these regions play a role in sensation seeking.” (Source)
  • Posterior insula - “Cytoarchitectonically complex and richly connected structure that functions as a cortical hub involved in interoception, multimodal sensory processing, autonomic control, perceptual self-awareness, and emotional guidance of social behavior.” (Source); “Recent studies of emotion have found that the anterior portion of the insula is activated when subjects recall or imagine events, whereas the posterior insula is activated by interpretation of current sensory information (49, 50).” (Source)
  • Bilateral temporal lobes - “They are most commonly associated with processing auditory information and with the encoding of memory. The temporal lobes are also believed to play an important role in processing affect/emotions, language, and certain aspects of visual perception.” (Source)
  • Pulvinar nucleus of the thalamus - “This thalamic nucleus is involved in behavioral orientation toward relevant stimuli, particularly directing visual attention (i.e., saccadic eye movement) toward visual stimuli (Blumenfeld 2002).” (Source)

The blood flow differences mentioned by the authors were that introverts tended to have more “frontally-based cognition” for recalling past events, planning for the future, problem solving, and the potential for self-talk or a running monologue. Meanwhile, they noted that the more activity in the anterior cingulate and posterior thalamus for extroverts may be evidence for “these individuals’ high drive for sensory and emotional stimulation.”

A study by Beukeboom et al also noted that introverts tend to prefer concrete details in conversations, while there were "significant positive correlations between extraversion and both language abstraction and self-reported level of interpretation." (Source)

I’m going to think aloud for a second, but this should be taken informally. It could also show how introverts and extroverts assess situations. Introverts may rely more on recognizing precedence for determining actions (such as pattern recognition or recalling both positive and negative outcomes from before.) Extroverts may be more focused on the current situation and how to react. I’d be interested in seeing if there’s current literature about this or if future studies could help investigate it. In the meantime, this paragraph is nothing more than speculation.

While the authors also note that their research does not “provide a definitive answer on the relationship between personality and brain activity”, they did acknowledge that it adds to the literature suggesting some personality traits are based on differences in brain function. This is in line with the interdisciplinary belief that personality is based on a combination of our biological, psychological (or adjusted), and social environments. In this case, introversion and extroversion would be seen as more biological.

What this helps to show is that introverts and extroverts may have different approaches to executive functioning such as nonverbal working memory, verbal working memory, emotional regulation, motivational regulation, and planning and problem-solving. We’ll look at individual differences with cortical arousal and anticipation next.

Onto Part 4 >

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