Neuropsychological Evidence of an Integrated Visuotactile Representation of Peripersonal Space in Humans

TLDR

Extinction is thought to arise from an imbalance between ipsilesional and contralesional spatial representations, a process that may involve bimodal premotor and parietal neurons with tactile hand fields and adjacent visual receptive fields. The study aimed to determine whether visual activation of peripersonal space can modulate the competition between left and right tactile representations in patients with tactile extinction. The hypothesis was examined in ten right‑hemisphere stroke patients exhibiting reliable tactile extinction. Visual peripersonal space centered on the hand modulates tactile perception, with near‑hand visual cues suppressing contralesional touch and enhancing contralesional touch when presented near the contralesional hand, while distant visual cues have minimal effect, confirming a hand‑centered visual peripersonal space that influences touch.

Abstract

Current interpretations of extinction suggest that the disorder is due to an unbalanced competition between ipsilesional and contralesional representations of space. The question addressed in this study is whether the competition between left and right representations of space in one sensory modality (i.e., touch) can be reduced or exacerbated by the activation of an intact spatial representation in a different modality that is functionally linked to the damaged representation (i.e., vision). This hypothesis was tested in 10 right-hemisphere lesioned patients who suffered from reliable tactile extinction. We found that a visual stimulus presented near the patient's ipsilesional hand (i.e., visual peripersonal space) inhibited the processing of a tactile stimulus delivered on the contralesional hand (cross-modal visuotactile extinction) to the same extent as did an ipsilesional tactile stimulation (unimodal tactile extinction). It was also found that a visual stimulus presented near the contralesional hand improved the detection of a tactile stimulus applied to the same hand. In striking contrast, less modulatory effects of vision on touch perception were observed when a visual stimulus was presented far from the space immediately around the patient's hand (i.e., extrapersonal space). This study clearly demonstrates the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception. These findings are explained by referring to the activity of bimodal neurons in premotor and parietal cortex of macaque, which have tactile receptive fields on the hand and corresponding visual receptive fields in the space immediately adjacent to the tactile fields.