The roads less travelled – four paths to get from touch to the body
I am studying medicine and as part of our course we do an Independent Learning project. I am doing mine in the Body in Mind research group here at NeuRA. My first task is to review a key paper in the field into which I’m about to delve. Here are my thoughts on Serino and Haggard’s paper “Touch and the Body” which was published this year in Neuroscience and Biobehavioural Reviews.
Serino and Haggard’s paper gives a four-part model that explains the notion that our sense of touch carries information about both the external object touching our skin and also our own body. Tactile information can influence (or be influenced by) our mental representation of the physical body. Mental body representations (MBR) are simply descriptions in our mind of the parts of the body, their position in space and their organization into a structural whole (us!)
S & H firstly examined the idea that the physical body structures tactile sensation – that when we touch or get touched, tactile afferents will map this into a homunculus, “little man”, in the parietal lobe of the brain. This information is conveyed to what’s known as S1 (the primary somatosensory cortex) of the opposite hemisphere.
Serino and Haggard’s second pathway explains that tactile information provides an important afferent input to mental body representations. Importantly they clarified the difference between body schema and body image; where body schema is short-lived and represents the positions of body parts in space, whereas body image remains fixed over time, representing a basic appearance of the body as an object in third person perspective.
Interestingly they reviewed how visual information relates to tactile sensation; the third pathway. They found that tactile acuity improved when subjects viewed the body. Moreover, this is independent from visuo-spatial orienting to the location of the body. The paper explained those with poor tactile ability will have vast improvements in tactile sensation when visual information is added. This has clinical implications for those with reduced sensation following brain lesions.
The last pathway explained how MBRs not only contribute to our body perception, but the perception of external objects. Basically, our touch of external objects is ‘body referenced’. This implies that MBRs are not just a stored body image; they are updated to integrate current sensory information.
So the first pathway tells the brain where we are being touched, the second pathway gives our brain a representation of what we are (our body image), the third is that this representation influences how we understand our sense of touch and the last being that our body image alters how external objects are perceived.
Nadia Barnsley is another of our superb third year medical students from the University of New South Wales. Her research interests include bodily awareness, body ownership and immune responses. She has already scored her first serious conference gig. Nadia is doing a very groovy experiment using fake arms and real people.
Serino A, & Haggard P (2010). Touch and the body. Neuroscience and biobehavioral reviews, 34 (2), 224-36 PMID: 19376156
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