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Aarlenne Z Khan, Yves Rossetti, J Douglas Crawford; Eye-centered remapping in patients with bilateral parietal lobe lesions. Journal of Vision 2003;3(9):391. doi: 10.1167/3.9.391.
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Previous studies have shown that normal subjects update visual space in eye-centered coordinates (Henriques et al. 1998). Furthermore, this remapping takes place in the posterior parietal cortex (Medendorp et al. 2002; Batista et al. 1999). Here we explore how updated information is retained in patients with bilateral posterior parietal lesions (optic ataxia (OA) patients). We recorded finger positions on two OA patients and five neurologically normal controls while they pointed to targets in the dark (head fixed). We compared two paradigms, 1) static, where Ss pointed to remembered peripheral targets and 2) dynamic, where Ss looked directly at a briefly presented target before looking away and then pointing to it. Ss performed these paradigms in two conditions, a) pointing immediately after the flashed target and b) pointing after a 5s delay. An eye-centered updating hypothesis predicts similarities in pointing errors between static and dynamic trials (slope of 1 when comparing the two) whereas a non- retinotopic hypothesis predicts a slope of 0. In controls, we found support for eye-centered updating during both immediate and delay conditions (average slope = 0.86) with no significant differences between the two. However, in our patients, we found significant differences between immediate and delayed trials with slopes of 0.41 and 0.76 respectively, indicating that although the patients could update information in an eye-centered frame, they could only do so after a certain time delay (five seconds). These results suggest that extra-PPC mechanisms (e.g. frontal cortex, superior colliculus) contribute to the updating of reaching space in an eye-centred frame, but cannot function optimally in the absence of the PPC.
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