Seminar: 4/13 - Henrik Ehrsson, Karolinska Institutet, Sweden
11:00 to 12:30 PM at: 5101 Tolman
Two legs, two arms, one head. Who am I?Ask any child if his hands belong to him and the answer will be "Of course!" But how does the brain actually identify its own body? In this talk I will describe how cognitive neuroscientists have recently begun to address this fundamental question. By clarifying how the normal brain produces a sense of ownership of one's body, we can learn to project ownership onto artificial bodies and simulated virtual ones; and even make two people have the experience of swapping bodies with one another. This could have ground-breaking applications in the fields of virtual reality and neuro-prosthetics.
Our hypothesis is that parts of the body are distinguished from the external world by the patterns they produce of correlated information from different sensory modalities (vision, touch and muscle sense). These correlations are hypothesized to be detected by neuronal populations that integrate multisensory information from the space near the body. We have recently used a combination of functional magnetic resonance imaging and human behavioral experiments to test these predictions. To change the feeling of body ownership, perceptual illusions were used where healthy individuals experienced that a rubber hand was their own, that a mannequin was their body, or, that they are outside their physical body and looking at it from the perspective of another individual ("out-of-body illusion"). Our behavioral results demonstrate that ownership of limbs and entire bodies depend on the temporal and spatial congruency of visual, tactile and proprioceptive signals in body-centered reference frames, and that the visual information from first person perspective plays a crucial role. Our imaging data show that neuronal populations in the premotor and intraparietal cortex are active when humans sense they own limbs or entire bodies, which supports the hypothesis that integration of multisensory information in body-centered coordinates is crucial for body ownership.