I remember well reading Rene Descartes' Discourse on Method in one of my first college philosophy classes. I couldn't believe that he was serious in separating his self from his body--arguing that while he could doubt the existence of his body, he could not doubt the existence of his self as a thinking being, because in the very activity of doubting, he would be thinking and thus showing his thinking self: I think, therefore I am. But, surely, I thought, our thinking self is always situated in our bodily self.
Years later, however, I learned from Oliver Sacks that some people can become so estranged from their bodies that they feel that some parts of their body are not really theirs, so that they might think their left leg is not theirs, but someone else's. In some rare cases, from a young age, people might obsessively want to amputate a healthy leg that seems alien to them. In such cases, there must be some malfunctioning of those parts of the brain that support our feeling of bodily self-ownership.
Over the past 30 years, neuroscientists who believe that the evolved purpose of the brain is to serve the survival and wellbeing of the body have studied how the brain creates our sense of owning our bodies. In recent years, I have become interested in this research as possibly providing neuroscientific confirmation for John Locke's principle of self-ownership as grounded in the body.
There have been four major approaches to the neuroscientific study of bodily self-ownership: mirror self-recognition, studies of the changes in corporeal awareness after brain damage, experiments inducing bodily illusions in healthy individuals, and studies of aberrant bodily experience in otherwise healthy people. I will briefly survey each of these areas of research.
The general conclusion from all of this research is that the brain has evolved neural networks for representing peripersonal space and body ownership that allows planning and executing movements that are good for the body, because they protect the body from external threats (physical and social), because they support social cooperation that benefits the body, and because they sustain the internal homeostatic health of the body (Barrett 2020; Craig 2015; Moseley et al. 2012; Tsakiris 2010, 2011).
One way to study bodily self-awareness is to devise experiments in which people look at body-parts, and the test is whether they can judge correctly whether this belongs to their body or not. One of the most common techniques is mirror self-recognition, in which individuals are tested to see if they can recognize their faces in a mirror. If they can recognize their face as their own, this indicates self-awareness (Gallup et al. 2011; Jeannerod 2003; Keenan et al. 2003).
Not only humans but also other animals have been tested in this way for mirror self-recognition. One common way to do this is to put a spot of brightly colored dye on the foreheads of some individuals. Then, when they see their faces in a mirror, they can show self-recognition by touching the colored spot and exploring it with the mirror.
Most animals cannot do this, because they react to their faces in a mirror as if these were the faces of others. I often see this in the spring, when a robin is staking out his territory around my house, and he repeatedly flies into the picture window of my house, because he sees his reflection and mistakes it for another robin invading his territory who needs to be driven away.
Among primates, monkeys can perceive faces, but only some of the great apes can recognize their own face in a mirror. About 75% of chimpanzees between the ages of 8 and 15 years can pass the mark test.
Most children can pass the test beginning sometime between 18 months and 2 years old. But some humans cannot recognize themselves in mirrors. Children younger than 18 months react to themselves in mirrors as if they were seeing other children. Some mentally disabled and autistic children do not show self-recognition. The same is true for some schizophrenics, for some people with brain damage, and some people with advanced Alzheimer's disease.
Self-recognition indicates the self-awareness that is a necessary condition for "mind-reading"--making inferences about mental states in others. To know what other people are thinking, we must build from our awareness of mental states in ourselves. Consequently, those who lack a deep self-awareness--such as severely autistic people--find it hard to read the minds of others, which impedes their understanding of and engagement in social interaction.
This self-awareness of our own minds and bodies that allows us to imagine the minds of others is the essential condition for what Locke presents as the natural understanding of the law of nature that dictates the equal liberty of all people. If I naturally desire to receive good from other people, then I should understand that other people have the like desire to receive good from me; and as I would desire to punish anyone who would injure me, then I should understand that anyone I would injure would have the like desire to punish me for injuring him. And just as I desire ownership of my own body and my natural rights to my life, liberty, and property as the necessary conditions for my body's survival and wellbeing, I can imagine that others have the like desire that I cannot frustrate without provoking their resentment and retaliatory punishment (Second Treatise, pars. 4-13). In this way, Locke suggests, reasoning from what we know from self-recognition about our own desires, we recognize others as having similar desires; and we then can understand why the mutual satisfaction of those desires requires that we respect those natural rights and duties that make peaceful social cooperation possible.
Since it secures the benefits of social cooperation, the mental capacity for self-recognition would have been advantageous for our evolutionary ancestors; and so we might expect that the human brain would have some evolved neural mechanisms for self-recognition. And indeed there is extensive evidence for a neural network in the human brain that enables self-recognition (Keenan et al. 2001; Platek et al. 2004; Gallup et al. 2011).
Early in this research, studies of split-brain patients made it clear that the right cortical hemisphere was more important for self-face recognition than the left hemisphere. Later research confirmed this through measuring reaction times in identifying one's own face as opposed to other faces. Left hands had faster reaction times than right hands in responding to self-faces but not to other faces. Other evidence came from patients with right hemisphere damage that makes it hard for them to identify their faces. Brain imaging studies showed that during the identification of self-faces, there was greater activation in the right frontal lobes, the right inferior parietal lobe, and the right insula.
Self-recognition, mental state attribution, and autobiographical memories share similar brain regions. One might expect this if self-awareness and mental state attribution are linked.
This is also connected to the neural correlates for contagious yawning--to tendency to yawn when one sees--or even thinks about--another person yawning. People who show contagious yawning recognize their own faces more quickly and score high on tests for mental state attribution (the ability to infer the mental states of others) (Platek et al. 2003). Brain imaging studies show that seeing someone yawn activates the posterior cingulate and the precuneus, which are areas of the brain related to self-awareness, theory of mind, and autobiographical memories (Platek et al. 2004).
Chimpanzees who are capable of self-recognition show contagious yawning (Anderson et al. 2004). Autistic children who show little self-recognition or mental state attribution do not show contagious yawning (Senju et al. 2007).
I will be writing more posts on the neuroscience of bodily self-ownership.
Anderson, J. R., Myowa-Yamakosh, M., and Matsuzawa, T. 2004. "Contagious Yawning in Chimpanzees." Proceedings of the Royal Society B 271: 468-70.
Barrett, Lisa Feldman. 2020. Seven and a Half Lessons About the Brain. New York: Houghton Mifflin Harcourt.
Craig, A. D. (Bud). 2015. How Do You Feel? An Interoceptive Moment with Your Neurobiological Self. Princeton, NJ: Princeton University Press.
Gallup, Gordon G., James R. Anderson, and Steven M. Platek. 2011. "Self-Recognition." In Shaun Gallagher, ed., The Oxford Handbook of the Self, 80-110. Oxford, UK: Oxford University Press.
Jeannerod, Marc. 2003. "The Mechanism of Self-Recognition in Humans." Behavioural Brain Research 142: 1-15.
Keenan, Julian Paul, Aaron Nelson, Margaret O'Connor, and Alvaro Pascual-Leone. 2001. "Self-Recognition and the Right Hemisphere." Nature 409: 305.
Keenan, Julian Paul, Gordon Gallup, and D. Falk. 2003. The Face in the Mirror: The Search for the Origins of Consciousness. New York: HarperCollins/Ecco.
Moseley, G. Lorimer, Alberto Gallace, and Charles Spence. 2012. "Bodily Illusions in Health and Disease: Physiological and Clinical Perspectives and the Concept of a Cortical 'Body Matrix.'" Neuroscience and Biobehavioral Reviews 36: 34-46.
Platek, Steven M., Samuel R. Critton, Thomas E. Myers, and Gordon G. Gallup. 2003. "Contagious Yawning: The Role of Self-Awareness and Mental State Attribution." Cognitive Brain Research 17: 223-27.
Platek, Steven M., Julian Paul Keenan, Gordon G. Gallup, and Feroze B. Mohamed. 2004. "Where Am I? The Neurological Correlates of Self and Other." Cognitive Brain Research 19: 114-122.
Senju, A., Maeda, M, Kikuchi, Y., Hasegawa, T., Tojo, V., and Osanai, H. 2007. "Absence of Contagious Yawning in Children with Autism Spectrum Disorder." Biology Letters 22: 706-708.
Tsakiris, Manos. 2010. "My Body in the Brain: A Neurocognitive Model of Body-Ownership." Neuropsychologia 48: 703-712.
Tsakiris, Manos. 2011. "The Sense of Body Ownership." In Shaun Gallagher, ed., The Oxford Handbook of the Self, 180-203. Oxford: Oxford University Press.