By Anna Gaziano
Numbers. Those arithmetical values that allow us to analyze and measure our surroundings. Without them, our understanding of the world we live in would be far less interesting. But what may be even more interesting is the way we process those numbers and how closely related that process is to spatial reasoning. The connection between space and numbers, specifically how we materialize values in our heads through mental number lines has been studied over the years, revealing that spatial orientation is incredibly important to this hypothetical number line. One study led by cognitive neuroscientist Stanislas Dehaene investigated how number magnitude is spatially organized in our minds and introduced the phenomenon of Spatial-Numerical Association of Response Codes, or the SNARC effect for short.
Imagine for a second feeling “overcomplete.” You have all of your limbs, and they are perfectly healthy. Yet, you feel as though your leg doesn’t belong to you. It shouldn’t be there, and you know it needs to go. The only way you can feel “whole” again is through its removal. You might be wondering why anyone would want to get rid of a perfectly healthy limb. Well, this phenomenon is the result of apotemnophilia, or Body Integrity Identity Disorder (BIID), a condition characterized “by the intense and long-standing desire for the amputation of a specific limb.” Most know exactly where they want the line of amputation to be, and this place stays fairly constant as time passes. Since it is rare for a surgeon to agree to amputate a healthy limb, many suffering from this condition will unfortunately resort to attempting the amputation themselves. In the past, this rare disorder was thought to be only psychological, and that perhaps the yearning for amputation was simply a way of seeking attention. However, in recent years, studies have shown otherwise.
One study performed by David Brang, Paul D. McGeoch and Vilayanur S. Ramachandran suggests that apotemnophilia is indeed a neurological disorder. The otherwise healthy subjects of the study went through a series of blind skin conductance response tests where they were pinpricked above and below the line where the amputation was. The responses to the pinpricking below the line were much greater than those above it. The resulting differences found suggest some abnormalities with the somatosensory input to the body part in question.
They suspect the disorder to be a consequence of damage to the right parietal lobe, which is responsible for processing sensory input from certain areas and forming our sense of body image. It could be the dysfunction within the right parietal lobe, specifically the right superior parietal lobe, causing irregular sympathetic output. The discrepancy between the signals and body image can lead to the feeling that a certain limb doesn’t belong and should be removed in order to feel “complete.” In addition, most patients have dealt with these feelings since childhood suggesting that the dysfunction is congenital.