Self-awareness in humans is more complex, diffuse than
previously thought
 |
 |
 |
 |
 |
 |
 |
 |
IMAGE: Researchers at the University of Iowa studied the brain of a
patient with rare, severe damage to three regions long considered integral to
self-awareness in humans (from left to right:...
Click here for more
information.
|
 |
 |
 |
 |
 |
 |
 |
 |
Ancient Greek philosophers considered the ability to "know thyself" as the
pinnacle of humanity. Now, thousands of years later, neuroscientists are trying
to decipher precisely how the human brain constructs our sense of self.
Self-awareness is defined as being aware of oneself, including one's traits,
feelings, and behaviors. Neuroscientists have believed that three brain regions
are critical for self-awareness: the insular cortex, the anterior cingulate
cortex, and the medial prefrontal cortex. However, a research team led by the
University of Iowa has challenged this theory by showing that self-awareness is
more a product of a diffuse patchwork of pathways in the brain – including other
regions – rather than confined to specific areas.
The conclusions came from a rare opportunity to study a person with extensive
brain damage to the three regions believed critical for self-awareness. The
person, a 57-year-old, college-educated man known as "Patient R," passed all
standard tests of self-awareness. He also displayed repeated self-recognition,
both when looking in the mirror and when identifying himself in unaltered
photographs taken during all periods of his life.
"What this research clearly shows is that self-awareness corresponds to a
brain process that cannot be localized to a single region of the brain," said
David Rudrauf, co-corresponding author of the paper, published online Aug. 22 in
the journal
PLOS ONE. "In all likelihood, self-awareness emerges from
much more distributed interactions among networks of brain regions." The authors
believe the brainstem, thalamus, and posteromedial cortices play roles in
self-awareness, as has been theorized.
The researchers observed that Patient R's behaviors and communication often
reflected depth and self-insight. First author Carissa Philippi, who earned her
doctorate in neuroscience at the UI in 2011, conducted a detailed self-awareness
interview with Patient R and said he had a deep capacity for introspection, one
of humans' most evolved features of self-awareness.
"During the interview, I asked him how he would describe himself to
somebody," said Philippi, now a postdoctoral research scholar at the University
of Wisconsin-Madison. "He said, 'I am just a normal person with a bad
memory.'"
Patient R also demonstrated self-agency, meaning the ability to perceive that
an action is the consequence of one's own intention. When rating himself on
personality measures collected over the course of a year, Patient R showed a
stable ability to think about and perceive himself. However, his brain damage
also affected his temporal lobes, causing severe amnesia that has disrupted his
ability to update new memories into his "autobiographical self." Beyond this
disruption, all other features of R's self-awareness remained fundamentally
intact.
"Most people who meet R for the first time have no idea that anything is
wrong with him," noted Rudrauf, a former assistant professor of neurology at the
UI and now a research scientist at the INSERM Laboratory of Functional Imaging
in France. "They see a normal-looking middle-aged man who walks, talks, listens,
and acts no differently than the average person."
"According to previous research, this man should be a zombie," he added. "But
as we have shown, he is certainly not one. Once you've had the chance to meet
him, you immediately recognize that he is self-aware."
Patient R is a member of the UI's world-renowned Iowa Neurological Patient
Registry, which was established in 1982 and has more than 500 active members
with various forms of damage to one or more regions in the brain.
The researchers had begun questioning the insular cortex's role in
self-awareness in a 2009 study that showed that Patient R was able to feel his
own heartbeat, a process termed "interoceptive awareness."
The UI researchers estimate that Patient R has ten percent of tissue
remaining in his insula and one percent of tissue remaining in his anterior
cingulate cortex. Some had seized upon the presence of tissue to question
whether those regions were in fact being used for self-awareness. But
neuroimaging results presented in the current study reveal that Patient R's
remaining tissue is highly abnormal and largely disconnected from the rest of
the brain.
"Here, we have a patient who is missing all the areas in the brain that are
typically thought to be needed for self-awareness yet he remains self-aware,"
added co-corresponding author Justin Feinstein, who earned his doctorate at the
UI in February. "Clearly, neuroscience is only beginning to understand how the
human brain can generate a phenomenon as complex as self-awareness."
###
The research team included Daniel Tranel, UI professor of neurology and
psychology and director of the Neuroscience Graduate Program; Gregory Landini,
UI professor of philosophy; Antonio Damasio, professor of neuroscience at the
University of Southern California; Sahib Khalsa, co-chief resident of psychiatry
at the University of California Los Angeles; and Kenneth Williford, associate
professor of philosophy and humanities at the University of Texas at
Arlington.
The National Institute of Neurological Disorders and Stroke, the National
Institute on Drug Abuse, the Mathers Foundation and the UI Carver College of
Medicine funded the research.
http://www.sciencedaily.com/releases/2012/08/120822181228.htm