New case studies focus on rare illusory body perceptions that could answer questions about how we maintain a "self"
September 21, 2010 ||
But sometimes this spatial self-location goes awry. During a so-called out-of-body experience, for example, one's self seems to be transported outside the physical body into a surreal perspective—some people even believe they are viewing their bodies from above, as though their true selves were floating. In a related experience, people with a delusion known as somatoparaphrenia disown one of their limbs or confuse another person's limb for their own. Such warped perceptions help researchers understand the neuroscience of selfhood.
A new paper offers examples of rare bodily illusions that are not confined to a single limb, nor are they complete out-of-body experiences—they are somewhere in between. These illusory body perceptions, described in the September issue of Consciousness and Cognition, could offer novel clues about how the brain maintains a link between the physical and conscious selves, or what the researchers call "bodily self-consciousness."
An out-of-body experience, Heydrich explains, warps all three aspects of bodily self-consciousness. In contrast, the two patients in the new study maintained normal self-location and first-person perspective even during an illusion. "They still perceived the world from their normal perspective, and they still felt they were in their bodies. But they had strong problem of self-identification. Patient 1 felt that…[the left]…half of him was a stranger and patient 2 felt that everything below his chin was no longer his."
Individuals who have trouble with only one aspect of bodily self-consciousness suggest that the three aspects can be dissociated, offering researchers an opportunity to determine which brain regions or networks underlie which components of self-perception.
An MRI revealed that patient 1 had a brain lesion in the right posterior intraparietal sulcus. In patient 2's brain, the researchers identified a concentration of aberrant electrical activity (the epileptogenic focus) in the right supplementary motor area (SMA) and right superior frontal gyrus. Surgery that removed patient 2's SMA and parts of his superior frontal gyrus cured the seizures and strange bodily perceptions, according to a checkup 15 months later. Heydrich says this implicates the SMA and premotor cortex specifically in the self-identification component of bodily self-consciousness.