Neuropsychological evidence of modular organization of the near peripersonal space.

Abstract

The space closely surrounding the body, near peripersonal space, is represented through multisensory coding, as witnessed by the spatial distribution of visual-tactile extinction in brain-damaged patients. Typically, tactile stimuli delivered on the contralesional hand are more severely extinguished by visual stimuli presented near to than far from the ipsilesional hand. To investigate whether the near peripersonal space is a unitary multisensory representation of the peribody space or is organized in a modular fashion, separately representing different body parts. Cross-modal extinction was used to assess right brain-damaged patients with left tactile extinction by presenting a combination of ipsilesional visual and contralesional tactile stimuli, both between homologous body parts (i.e., the two hands and sides of the face) and between nonhomologous body parts (i.e., right hand + left face and right face + left hand). Visual-tactile extinction observed in the near peripersonal space of homologous body parts was more severe than that obtained between nonhomologous body parts. In contrast, cross-modal extinction observed in the far peripersonal space was overall weak and comparable when stimulating homologous or nonhomologous body sectors. In addition, a clear near-far modulation of visual-tactile extinction was obtained only when stimulating homologous, but not nonhomologous, body parts. These findings were observed irrespective of the severity of unisensory tactile extinction. Near peripersonal space is not unitary but is functionally organized in modules and consists of at least two different spatial representations, one around the hand and another around the face, which might be selectively affected in patients with extinction.