Location of the Mind Remains a Mystery

ResearchBlogging.orgWhere does the mind reside? It’s a question that has occupied the best brains for thousands of years, including the Buddha’s.

Recent advances in functional magnetic resonance neuroimaging, a technique that measures brain activity in the hope of finding correlations between mental functions and specific regions of the brain, have led to a wealth of studies that map particular functions onto regions. Self-awareness is defined as being aware of oneself, including one’s traits, feelings, and behaviors. Previous neuroimaging studies had suggested that self-awareness (SA), which is central to human consciousness, depends critically on specific brain regions, namely the insular cortex, the anterior cingulate cortex (ACC), and the medial prefrontal cortex (mPFC). This proposal predicts that damage to these regions should disrupt or even abolish SA — an afflicted individual should be like a zombie, according to David Rudrauf, a neurologist at the University of Iowa in Iowa City.

University of Iowa researchers studied the brain of a patient with damage to three regions long considered integral to self-awareness — left to right, the insular cortex, anterior cingulate cortex, and medial prefrontal cortex. Image credit: UI Department of Neurology.

So when Rudrauf and his team heard about patient R, they immediately thought he could help set the record straight. Patient R is a 57-year-old man whose brain was damaged in 1980 following a severe episode of herpes simplex encephalitis. His brain damage is bilateral, more extensive on the right, and encompasses the target regions mentioned above: the insular cortex, the ACC, and the mPFC. Rudrauf et al reasoned that if any of the structures that are damaged in this patient are indeed critical for the different aspects of SA implicated by the hypothesis described above — i.e., insula, ACC, mPFC — the patient should show clear disruptions of the corresponding functions. Conversely, if these structures are not critical, R should show largely preserved SA.

In fact, R displays a strong concept of selfhood. Rudrauf’s team confirmed this by checking whether he could recognize himself in photographs and by performing the tickle test — based on the observation that you can’t tickle yourself. They concluded that many aspects of R‘s self-awareness remained unaffected. “Having interacted with him it was clear from the get go that there was no way that [the theories based on neuroimaging] could be true,” says Rudrauf. R also has an IQ within the normal range, although he does have severe amnesia, which prevents him from learning new information, and he struggles with social interaction.

The UI researchers estimate that 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 R’s remaining tissue is highly abnormal and largely disconnected from the rest of the brain.

The authors of the report conclude that:

R is a conscious, self-aware, and sentient human being despite the widespread destruction of cortical regions purported to play a critical role in SA, namely the insula, anterior cingulate cortex, and medial prefrontal cortex.

“Self-awareness corresponds to a brain process that cannot be localized to a single region of the brain,” says Rudrauf. “In all likelihood, self-awareness emerges from much more distributed interactions among networks of brain regions.”

Patient R demonstrates that the mind remains as elusive as ever.

References:

  • Philippi CL, Feinstein JS, Khalsa SS, Damasio A, Tranel D, & et al. (2012). Preserved Self-Awareness following Extensive Bilateral Brain Damage to the Insula, Anterior Cingulate, and Medial Prefrontal Cortices Plos ONE, 7 (8) DOI: 10.1371/journal.pone.0038413
Advertisements

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s