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Mark W. Greenlee, Steven Blurton, Markus Raabe; Functional MRI analysis of cortical activation during saccadic adaptation. Journal of Vision 2009;9(8):401. doi: 10.1167/9.8.401.
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Saccadic adaptation is a mechanism to preserve accuracy during changes in the oculomotor system. Adaptation occurs when a visual target is repeatedly displaced during a saccade, so that the original saccade either overshoots the target or falls short of it. Though many primate studies emphasize the role of the cerebellum in this process and a PET study revealed activation in cerebellar neurons (Desmurget et al. Nat Neurosc., 1998, 1, 524–8), the exact neuronal substrate of saccadic adaptation remains unclear. We investigated the neural correlates of inward and outward saccadic adaptation using a gaze-dependent visual display in fMRI. Subjects were asked to saccade from fixation to a target as quickly as possible. Saccadic gain adaptation was experimentally induced using the double step paradigm: During the adaptation phase, the target was displaced peri-saccadically by 30%. In control condition, however, the displacement was done post-saccadically, delayed by 300 ms related to saccade onset. The experiment comprised 480 trials in all, arranged in (a) pre-adaptation (control), (b) adaptation and (c) post-adaptation (control) phases. Functional MR images (Siemens 3T) and eye movements from 12 subjects were recorded simultaneously. Data was preprocessed and statistically analysed using SPM5. The SPMs which resulted from our random effects analysis were initially thresholded with p uncorrected[[lt]]0.001. Clusters surpassing a threshold of p corrected[[lt]]0.05 were considered as significantly activated. The eye movement data indicate a significant (T = 2.57; p [[lt]]0.05) decrease in gain (12 percent on average) during (b), which was accompanied by bilateral enhanced activity in the posterior parieto-insular cortex when compared with (a). This region is involved in processing of vestibular information in primates and part of a cortical network labelled parieto-insular vestibular cortex (PIVC; Eickhoff et al. Hum. Brain Mapp., 2006, 27, 611–21). The enhanced activation probably reflects an integration of information regarding head position and oculomotor information.
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