Have you ever heard of nomofobia, a fear of not being able to check your phone regularly? Are you going crazy when forget your charger home? Have you ever freaked out because you reached an area without reception? Would you return and go home immediately because you left your phone home? You know what we are talking about. But is there an evidence for tools that we use regularly "grow" on us, furthermore, become the part of our body schema?
The way we perceive our body is crucial for knowing our place in the world. Literally speaking, the information from our joints and muscles provide the baseline to coordinate our movements and actions. The so called proprioceptive set of stimuli arriving to the central nervous system is often not conscious, but always stored in comparison with other modalities such as visual information (looking in the mirror for eg.). This purely perceptive, on-line, plastic representation of our body is often referred to as 'body scheme' in neurology. The body schema is actually a working model, a helpful one, that can help anchor motor commands to the current position and state of the body. It is transient in nature, and its disturbance can lead extreme cases as described by Oliver Sacks (read on Oliver Sacks's terminal disease here):
In that instant, that very first encounter, I knew not my leg. It was utterly strange, notmine unfamiliar. I gazed upon it with absolute non-recognition […] The more I gazed at that cylinder of chalk, the more alien and incomprehensible it appeared to me. I could no longer feel it as mine, as part of me. It seemed to bear no relation whatever to me. It was absolutely not-me – and yet, impossibly, it was attached to me – and even more impossibly, continuous with me .
Oliver Sacks: A Leg to Stand On (1991)
Body image, however, is the conscious concept about our body, that is "on the surface", it is the summation of the attitudes towards our body, thats one object of the environment. This knowledge is highly semantic and is closely related to our cognitive (I am fat), affective (I am ugly) and behavioural (self-punishing behaviours) interactions with our own self. In fact, as Mahler claims, having a body image is one of the first steps of having a self by differentiating ourselves from our mother. (Longo et al, 2000).
But how can we connect all this concepts to what is actually happening in the brain? Neuroscientific research is mostly focused on the body scheme, since it is much easier to operationalize in primates. The concept of body map and somatotopic representation (A.K.A humunculus) is one of the first main findings of neuroscience, as it proves the premise of functional localisation in the brain. As Maravita and Iriki describes, the action-specificity of the body scheme (the fact that we fine-tune our movements compared to our position and previous movements) is pinned down to the frontoparietal network. More precisely, the receptive field of the neurons is "bimodal". For example, in a way that they respond with elevated firing rate to sensory and proprioceptive stimuli if it comes from the same "gestalt", the movement of the same limb or body part (interestingly that is not the case with fine movements, finger movement is encoded in a different way).
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| Macaque selfie - strangely relevant to this post |
How can we answer body schema-related questions in primates? One clever way of doing it is via tool use: the macaques were put in cages where it was impossible to reach the food that was put outside of the cage, unless they used a rake to pull the food towards themselves. After several days, the neurons of the frontoparietal network, that initially responded to the hand-related visual or proprioceptive information expanded to the rake, but only if the rake was used to grabbing food (only if the ACTION was functional).
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source : http://tinyurl.com/oa4x8mz |
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| Characteristic neglect-bias in a drawing task. See the podcast for further information |
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