Abstract
Anti-saccades are eye movements that require inhibition to stop the automatic saccade to the visual target and to perform instead a saccade in the opposite direction. The inhibitory processes underlying anti-saccades have been primarily associated with frontal cortex areas for their role in executive control. Impaired performance in anti-saccades has also been associated with the parietal cortex, but its role in inhibitory processes remains unclear. Here, we tested the assumption that the dorsal parietal cortex contributes to spatial inhibition processes of contralateral visual target. We measured anti-saccade performance in 2 unilateral optic ataxia patients and 15 age-matched controls. Participants performed 90 degree (across and within visual fields) and 180 degree inversion anti-saccades, as well as pro-saccades. The main result was that our patients took longer to inhibit visually guided saccades when the visual target was presented in the ataxic hemifield and the task required a saccade across hemifields. This was observed through anti-saccades latencies and error rates. These deficits show the crucial role of the dorsal posterior parietal cortex in spatial inhibition of contralateral visual target representations to plan an accurate anti-saccade toward the ipsilesional side.
Highlights
Anti-saccades are eye movements directed to a location opposite to a presented stimulus (Hallett 1978; Mokler and Fischer 1999; Munoz and Everling 2004)
We investigated the accuracy of correct saccades for all participants
For the classic and mirror saccades, patients showed a large increase in variability and appeared to need more saccades than controls to reach the intended goal. They seemed to make more variable or erroneous saccades when the visual target was presented in the left hemifield; these were corrected with subsequent saccades
Summary
Anti-saccades are eye movements directed to a location opposite to a presented stimulus (Hallett 1978; Mokler and Fischer 1999; Munoz and Everling 2004). Preparatory set or proactive inhibition refers to top-down inhibition that is present before the stimulus appears and entails a global inhibition from making an eye movement (Funahashi et al 1993; Everling and Munoz 2000; Barash and Zhang 2006; Sharpe et al 2011; Coe and Munoz 2017; Jahanshahi and Rothwell 2017; Fernandez-Ruiz et al 2018) This top-down inhibition appears to be nonspatial, suppressing automatic saccades to the visual target regardless of its location (Guitton et al 1985; Barash and Zhang 2006) and nonspecific to anti-saccades; pro-saccade latencies are increased during interleaved. A lack of spatial inhibition would result in greater error rates (ERs) for anti-saccades in which the visual target location was not sufficiently inhibited, for example, due to damage to connectivity, rather than overall increased ERs regardless of location, more associated with response inhibition
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