Neuroimaging studies reveal that a wrinkly cerebral cortex is what distinguishes human thinking from other animals'
The computer, smartphone or other electronic device on which you are reading this article has a rudimentary brain—kind of.* It has highly organized electrical circuits that store information and behave in specific, predictable ways, just like the interconnected cells in your brain. On the most fundamental level, electrical circuits and neurons are made of the same stuff—atoms and their constituent elementary particles—but whereas the human brain is conscious, manmade gadgets do not know they exist. Consciousness, most scientists argue, is not a universal property of all matter in the universe. Rather, consciousness is restricted to a subset of animals with relatively complex brains. The more scientists study animal behavior and brain anatomy, however, the more universal consciousness seems to be. A brain as complex as the human brain is definitely not necessary for consciousness. On July 7 this year, a group of neuroscientists convening at Cambridge University signed a document officially declaring that non-human animals, “including all mammals and birds, and many other creatures, including octopuses” are conscious.
Humans are more than just conscious—they are also self-aware. Scientists differ on the difference between consciousness and self-awareness, but here is one common explanation: Consciousness is awareness of one’s body and one’s environment; self-awareness is recognition of that consciousness—not only understanding that one exists, but further understanding that one is aware of one’s existence. Another way of thinking about it: To be conscious is to think; to be self-aware is to realize that you are a thinking being and to think about your thoughts. Presumably, human infants are conscious—they perceive and respond to people and things around them—but they are not yet self-aware. In their first years of life, infants develop a sense of self, learn to recognize themselves in the mirror and to distinguish their own point of view from other people’s perspectives.
Numerous neuroimaging studies have suggested that thinking about ourselves, recognizing images of ourselves and reflecting on our thoughts and feelings—that is, different forms self-awareness—all involve the cerebral cortex, the outermost, intricately wrinkled part of the brain. The fact that humans have a particularly large and wrinkly cerebral cortex relative to body size supposedly explains why we seem to be more self-aware than most other animals.
One would expect, then, that a man missing huge portions of his cerebral cortex would lose at least some of his self-awareness. Patient R, also known as Roger, defies that expectation. Roger is a 57-year-old man who suffered extensive brain damage in 1980 after a severe bout of herpes simplex encephalitis—inflammation of the brain caused by the herpes virus. The disease destroyed most of Roger’s insular cortex, anterior cingulate cortex (ACC), and medial prefrontal cortex (mPFC), all brain regions thought to be essential for self-awareness. About 10 percent of his insula remains and only one percent of his ACC.
Roger cannot remember much of what happened to him between 1970 and 1980 and he has great difficulty forming new memories. He cannot taste or smell either. But he still knows who he is—he has a sense of self. He recognizes himself in the mirror and in photographs. To most people, Roger seems like a relatively typical man who does not act out of the ordinary.
Carissa Philippi and David Rudrauf of the University of Iowa and their colleagues investigated the extent of Roger’s self-awareness in a series of tests. In a mirror recognition task, for example, a researcher pretended to brush something off of Roger’s nose with a tissue that concealed black eye shadow. 15 minutes later, the researcher asked Roger to look at himself in the mirror. Roger immediately rubbed away the black smudge on his nose and wondered aloud how it got there in the first place.
Philippi and Rudrauf also showed Roger photographs of himself, of people he knew and of strangers. He almost always recognized himself and never mistook someone else for himself, but he sometimes had difficulty recognizing a photo of his face when it appeared by itself on a black background, absent of hair and clothing.
Roger also distinguished the sensation of tickling himself from the feeling of someone else tickling him and consistently found the latter more stimulating. When one researcher asked for permission to tickler Roger’s armpits, he replied, “Got a towel?” As Philippi and Rudrauf note, Roger’s quick wit indicates that in addition to maintaining a sense of self, he adopts the perspective of others—a talent known as theory of mind. He anticipated that the researcher would notice his sweaty armpits and used humor to preempt any awkwardness.
In another task, Roger had to use a computer mouse to drag a blue box from the center of a computer screen towards a green box in one of the corners of the screen. In some cases, the program gave him complete control over the blue box; in other cases, the program restricted his control. Roger easily discriminated between sessions in which he had full control and times when some other force was at work. In other words, he understood when he was and was not responsible for certain actions. The results appear online August 22 in PLOS One.
Given the evidence of Roger’s largely intact self-awareness despite his ravaged brain, Philippi, Rudrauf and their colleagues argue that the insular cortex, anterior cingulate cortex (ACC), and medial prefrontal cortex (mPFC) cannot by themselves account for conscious recognition of oneself as a thinking being. Instead, they propose that self-awareness is a far more diffuse cognitive process, relying on many parts of the brain, including regions not located in the cerebral cortex.
In their new study, Philippi and Rudrauf point to a fascinating reviewof children with hydranencephaly—a rare disorder in which fluid-filled sacs replace the brain’s cerebral hemispheres. Children with hydranencphaly are essentially missing every part of their brain except the brainstem and cerebellum and a few other structures. Holding a light near such a child’s head illuminates the skull like a jack-o-lantern. Although many children with hydranencephaly appear relatively normal at birth, they often quickly develop growth problems, seizures and impaired vision. Most die within their first year of life. In some cases, however, children with hydranencephaly live for years or even decades. Such children lack a cerebral cortex—the part of the brain thought to be most important for consciousness and self-awareness—but, as the review paper makes clear, at least some hydranencephalic children give every appearance of genuine consciousness. They respond to people and things in their environment. When someone calls, they perk up. The children smile, laugh and cry. They know the difference between familiar people and strangers. They move themselves towards objects they desire. And they prefer some kinds of music over others. If some children with hydranencephaly are conscious, then the brain does not require an intact cerebral cortex to produce consciousness.
Whether such children are truly self-aware, however, is more difficult to answer, especially as they cannot communicate with language. In D. Alan Shewmon‘s review, one child showed intense fascination with his reflection in a mirror, but it’s not clear whether he recognized his reflection as his own. Still, research on hydranencephaly and Roger’s case study indicate that self-awareness—this ostensibly sophisticated and unique cognitive process layered upon consciousness—might be more universal than we realized.
*If you printed out this article, kudos and thanks for reading!
Merker B (2007) Consciousness without a cerebral cortex: A challenge for neuroscience and medicine. Behavioral and Brain Sciences 30: 63-81.
Philippi C., Feinstein J.S., Khalsa S.S., Damasio A., Tranel D., Landini G., Williford K.5, Rudrauf D. Preserved self-awareness following extensive bilateral brain damage to the insula, anterior cingulate, and medial prefrontal cortices. PLOS ONE. Aug 22.
Shewmon DA, Holmes GL, Byrne PA. Consciousness in congenitally decorticate children: developmental vegetative state as self-fulfilling prophecy. Dev Med Child Neurol. 1999 Jun;41(6):364-74.
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