Control of Reflexive Saccades following Hemispherectomy

Abstract

Abstract■ Individuals who have undergone hemispherectomy for treatment of intractable epilepsy offer a rare and valuable opportunity to examine the ability of a single cortical hemisphere to control oculomotor performance. We used peripheral auditory events to trigger saccades, thereby circumventing dense postsurgical hemianopia. In an antisaccade task, patients generated numerous unintended short-latency saccades toward contralesional auditory events, indicating pronounced limitations in the ability of a single hemicortex to exert normal inhibitory control over ipsilateral (i.e., contralesional) reflexive saccade generation. Despite reflexive errors, patients retained an ability to generate correct antisaccades in both directions. The prosaccade task revealed numerous contralesional express saccades, a robust contralesional gap effect, but the absence of both effects for ipsilesional saccades. These results indicate limits to the saccadic control capabilities following hemispherectomy: A single hemicortex can mediate antisaccades in both directions, but plasticity does not extend fully to the bilateral inhibition of reflexive saccades. We posit that these effects are due to altered control dynamics that reduce the responsivity of the superior colliculus on the intact side and facilitate the release of an auditory-evoked ocular grasp reflex into the blind hemifield that the intact hemicortex has difficulty suppressing. ■

The comparative anatomy of frontal eye fields in primates

“…These later studies clearly demonstrated that the common area of damage between patients affected the precentral sulcus, between the superior and inferior frontal sulci, and the adjacent parts of the precentral and middle frontal gyri ( Figure 2). Note that, as in the monkey, unilateral FEF lesions present mainly contralateral saccade impairment (but see Reuter-Lorenz et al, 2011). In a more general point of view, human studies for the most part are consistent with the findings reported in monkeys, namely lesions of the peri-precentral cortex in humans and adjacent to the arcuate sulcus in monkeys lead to voluntary saccadic eye movements impairments.…”

Pro- and antisaccades in children elicited by visual and acoustic targets - does modality matter?

“…No auditory gap effect was found for SRTs or error rates. In contrast to this, previous findings in adults have described a smaller, but still significant gap effect for acoustically cued saccades [ 17 , 23 - 25 ]. It might be the case for children that although mean SRTs indicate a gap-effect, it is obscured by a relatively high SRT variablity (208 ms gap, 209 ms overlap condition).…”

“…This reaction is already present in babies [ 16 ]. Although saccades towards acoustic targets are scientifically less well investigated than saccades towards visual targets, a recent study delineated an "acoustic-evoked ocular grasp reflex" in adults [ 17 ].…”

“…The vast majority of studies on saccades triggered by acoustic targets only investigated prosaccades. Until now there are only two studies, which investigated acoustically triggered antisaccades in adults [ 17 , 26 ]. One of these studies [ 17 ] studied acoustic antisaccades in three patients with hemispherectomy and a control group.…”

“…Until now there are only two studies, which investigated acoustically triggered antisaccades in adults [ 17 , 26 ]. One of these studies [ 17 ] studied acoustic antisaccades in three patients with hemispherectomy and a control group. They revealed that patients generated more errors and showed longer SRTs than control participants.…”