Binding personal and peripersonal space: evidence from tactile extinction

Behavioral and neurophysiological studies suggest that the brain constructs different representations of space. Among these representations are personal and peripersonal space. Personal space refers to the space occupied by our bodies. Peripersonal space refers to the space surrounding our bodies, which can be reached by our limbs. How these two representations are bound to give a unified sense of space in which humans act is not clear. We tested 10 patients with tactile extinction to investigate this issue. Tactile extinction is an attentional disorder in which patients are unaware of being touched on their contralesional limb if they are also touched simultaneously on their ipsilesional limb. We hypothesized that mechanisms that bind personal and peripersonal representations would improve these patients' awareness of being touched on their contralesional limbs. Visual--tactile integration and intentional movements were considered candidate mechanisms. Patients were more likely to be aware of contralesional touch when looking towards their contralesional limb than when looking towards their ipsilesional limb, and when actively moving on tactile probes than when receiving tactile stimuli passively. The improved awareness of being touched on the contralesional limb under these conditions suggests that cross-sensory and sensorimotor integration help bind personal and peripersonal space.