Moheb Costandi’s title is taken from Nietzsche’s philosophical masterpiece Thus Spoke Zarathustra: “The awakened and knowing say: body am I entirely, and nothing more; and soul is only the name for something about the body.” The radical rejection of mind-body dualism expressed in this sentence is shared today by most neuroscientists, who believe that the mind is a product of the brain. Indeed, this “neurocentric” view has been widely accepted and, writes Costandi, “the idea that we are our brains is now firmly established”.
Yet this has given rise to a new dualism, one in which the body and the brain are seen as separate entities. This is what Costandi – a science writer who trained as a neuroscientist – seeks to correct in his illuminating and detailed investigation into how our understanding of the brain and its role in shaping our sense of self has evolved across the last 200 years, and what today’s research in neuroscience, psychiatry and psychology tells us about the relationship between brain and body. He writes: “The brain does not exist in isolation; it is one part of a complex and dynamic system that also includes the body and the environment.”
This might seem obvious, but it leads to some mind-boggling conclusions. Crucially, Costandi seeks to expand the idea of consciousness from merely the subjective experience of events in the outside world to self-consciousness, which sounds like embarrassment but in fact refers to the self being largely defined through an awareness of the body and its surroundings: I sense therefore I am.
The brain constantly receives sensory information about the body – pain signals from our skin, internal sensations, the sight of our limbs as they move – and from this it creates maps and models of it (and indeed of the space around it, up to about an arm’s length). “Our body is our brain’s user interface, an object – or tool – with which we perceive and interact with the world.” What we each call “me” is the result of this bodily perception, and not, as you might assume, some effusion conjured by the brain on its own.
It follows that our sense of self is malleable, for the brain is constantly changing its model of the body. Costandi views the bodily self as being like “a jigsaw puzzle, constructed anew minute by minute within the brain”, pieced together from fragments of sensory data. The extraordinarily complex nature of this fragmentary self is exposed when these streams of sense data are disturbed.
To illustrate this, Costandi describes a remarkable illusion designed to trick the brain. A person sits at a table and places their left arm beneath it, while on top of it a realistic, lifesize rubber hand is positioned in front of them. As they watch, a researcher simultaneously strokes the hidden hand and the rubber one with a soft paint brush. Someone who took part in the experiment reported: “I found myself looking at the dummy hand thinking it was actually my own.” When asked to close their eyes and point at their left index finger, the person pointed to the rubber hand. As Costandi says, this illusion creates “a conflict between what we see and what we feel, and the brain resolves the conflict by updating its internal models, substituting the fake hand for the real one”.
That this can lead to a completely new sense of self is illustrated more dramatically by the effects of brain injury or disease. Disturbed or distorted maps can play a devastating role in serious mental illnesses such as anorexia and schizophrenia. Indeed, the latter has been described as a disturbance in which “the boundaries of the self become loose or blurred” so that “the patient may feel … that parts of his body do not belong to him or that he is part of the plants, animals, clouds, other people or of the whole world and that they are part of him”.
Anomalies in body maps may also help explain body integrity identity disorder, “a rare and mysterious condition” first described in 1977 which drives people to amputate healthy limbs. One patient felt compelled to blast his own leg with a shotgun, telling doctors: “If I die in the next instant, I don’t care, because I have finally realised myself. I have become whole.”
According to Costandi, “consciousness is the biggest scientific mystery of all”. The revolutionary findings that have emerged from the study of bodily awareness over the last two decades are prompting some researchers to redefine what it means to be conscious. From elephants recognising themselves in mirrors (a yardstick for self-awareness) to insects with bodily awareness, the phenomenon turns out to be far more widespread than was once believed. Perhaps one day we will have to acknowledge that robots, too, can possess a degree of self-consciousness. Costandi’s fascinating study reveals the astonishingly subtle and intricate relationship that exists between our brains and our bodies, and shows how fragile – but also how wondrous – our sense of self really is.
• Body Am I: The New Science of Self-Consciousness, by Moheb Costandi is published by MIT (£22.50). To support the Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.