Uni- and cross-modal temporal modulation of tactile extinction in right brain damaged patients

The influence of ipsilesional tactile and visual stimuli on the ability to detect contralesional tactile stimuli was investigated in eight right brain damaged patients (RBD) with tactile extinction and in eight healthy subjects by delivering a series of single and double stimuli. Double stimuli were unimodal (tactile or visual) or cross-modal (tactile and visual) and could be delivered simultaneously or sequentially at three possible intervals (65, 125, 305 ms). In sequential double trials, left-sided stimuli preceded or followed right-sided stimuli. Subjects were asked to verbally report number (1 or 2), side (left or right) and modality (tactile, visual, visuo-tactile). Control subjects were highly accurate in detecting single and double stimuli. RBD patients detected all right-sided stimuli and left single visual or tactile stimuli with high accuracy; however, they omitted left-sided tactile stimuli in a high proportion of double trials due to the presence of tactile extinction. Omissions of left-sided tactile stimuli were minimal at the longest SOA. Moreover, at 0 and 65 ms SOA omissions were significantly higher in unimodal than in cross-modal combinations. This figure indicates that detection of contralesional tactile stimuli is modulated over time both uni- and cross-modally.