Our brains contain a highly distorted model of our own bodies, according to new research.
Scientists at the University College of London Institute of Cognitive Neuroscience have recently discovered that our brains do not always perceive our bodies accurately.
Dr. Matthew Longo and his team of researchers focused on the brain’s perception of the hand. The brain has several different mechanisms by which it views the body. In addition to visual perception and memory, the brain also uses a sense known as “proprioception,” or position sense. Proprioception is the brain’s way of using the nervous system input from skin, muscles and joints in knowing where the body is in space.
One goal of this study was to begin to discover how the sense of proprioception works, and how the brain is able to know where all the parts of the body are in space, even with the eyes closed. In addition to nervous system input from joints, muscles and skin, neuroscientists think that the brain must have some type of stored body image to map the size and shape of each body part.
Longo asked participants in the study to put their left hands palm down under a board and judge the location of the covered hand’s knuckles and fingertips by pointing to where they perceived each of these landmarks. A camera situated above the experiment recorded exactly where the participant pointed. By putting together the locations of all the landmarks, the researchers reconstructed the brain’s model of the hand, and revealed the significant differences between the actual and perceived hand.
The participants on average perceived their hands to be approximately two-thirds wider and one-third shorter than their hands were in reality.
When asked to identify their own hand from a set of photographed hands with various distortions in shape, the participants were easily able to do so, demonstrating that they did in fact know what their hand really looked like.
“Of course we know what our hand really looks like,” said Dr. Longo. “There is clearly a conscious visual image of the body as well. But that visual image of the body seems not to be used for position sense.”
It is possible that the misperceptions of size and shape in the hand are related to the way that the brain models different parts of the skin. Or that the model is affected by the amount of nervous system input from different areas of the skin.
The study participants were healthy, and had healthy perceptions of their body image. They perceived their overall bodies accurately. While the participant’s sense of proprioception perceived their hands as wider and shorter, these findings do not necessarily generalize to a perception of their entire body as wider and shorter, or mean that a healthy individual would do so.
However, as Dr. Longo states, “These findings may well be relevant to psychiatric conditions involving body image such as anorexia nervosa, as there may be a general bias towards perceiving the body to be wider than it is. Our healthy participants had a basically accurate visual image of their own body, but the brain’s model of the hand underlying position was highly distorted. This distorted perception could come to dominate in some people, leading to distortions of body image as well, such as in eating disorders.”
“The phrase ‘I know the town like the back of my hand’ suggests that we have near-perfect knowledge of the size and position of our body parts, but this may not be the case,” says Longo.
This study was funded by the Biotechnology and Biological Science Research Council.
Source: University College London, Proceeding of the National Academy of Sciences of the United States of America