Wednesday, August 16, 2006

The Neural Basis of Embodyment

Some edited clips from a recent J. Neuroscience article by Arzy et al. :

Embodiment, the sense of being localized within one's physical body, is a fundamental aspect of the self. Recent evidence has started to show that self and body processing require two distinct brain mechanisms, with key loci in the temporoparietal junction (TPJ) - involved in self processing and multisensory integration of body-related information - and the extrastriate body area (EBA) - which responds selectively to human bodies and body parts. Arzy et al have used evoked potential mapping to show that activations in EBA and TPJ code differentially for embodiment and self location, because the location and timing of brain activation depended on whether mental imagery is performed with mentally embodied (EBA) or disembodied (TPJ) self location. In a second experiment, they showed that only EBA activation, related to embodied self location, but not TPJ activation, related to disembodied self location, was modified by the subjects' body position during task performance (supine or sitting). This suggests that embodied self location and actual body location share neural mechanisms.

Figure. To investigate embodiment and self location, subjects were asked to perform two mental-imagery tasks with respect to their own body in response to a schematic front- or back-facing human figure. In an own-body transformation task, (OBT task) subjects were asked to imagine themselves in the position and orientation of a schematic human figure, as shown on a computer screen (bottom row, the correct responses for each task are indicated under each stimulus) Either the right or left hand of the figure was marked, and subjects indicated which hand was marked. In a mirror task (MIR task), the same schematic human figure was shown, but subjects were instructed to imagine that the schematic figure (as shown on the computer screen) was their mirror reflection, as seen from their habitual point of view ( top row, the correct responses for each task are indicated under each stimulus).

Figure. Generators of mirror task (MIR. top row, were localized at the left EBA and of the own body transformation task (OBT, bottom row) at the right TPJ and left EBA

Figure. EBA. The mean (x, y) Talairach coordinates of the EBA are given for several neuroimaging studies. Note the similarity of EBA localization across studies, neuroimaging techniques, and behavioral tasks.

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