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So Young Moon, Matthew S. Cain, Frida E. Polli, Jason J. Barton, Dara S. Manoach; Signal timing and hemispheric localization in the human saccadic system: Preparatory processes and the sensorimotor transformation for antisaccades. Journal of Vision 2005;5(8):586. doi: 10.1167/5.8.586.
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Objectives: We used event-related functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) to observe signal timing and hemispheric localization in the human saccadic system for preparatory processes and the sensorimotor transformation.
Methods: We carried out fMRI on 21 and MEG on 17 healthy subjects, using the same saccadic paradigm. Subjects performed blocks of randomly mixed prosaccade and antisaccade trials. A cue for prosaccades or antisaccades was presented for 300 ms and was then replaced by the fixation ring. After 1700 ms the fixation ring disappeared and a target appeared around one of the two peripheral dots for 1 s. After that, the fixation point reappeared and lasted for 1 s.
Results: In fMRI, beginning shortly after the cue, hemodynamic activity in the frontal eye field (FEF) and supplementary eye field (SEF) reached a peak at 4 s post-cue. Activity in superior temporal gyrus, inferior frontal gyrus, and posterior cingulate gyrus decreased after the cue and showed a negative peak at 4 s post-cue. Activity in the parietal eye field (PEF) showed a later peak at 4 s post-target (i.e. 6 s post-cue). Activity in the FEF, SEF, and PEF was greater during antisaccades than prosaccades. In MEG, the left FEF showed increased neural activity after the cue but 605–755 ms prior to the target, irrespective of the saccadic direction. During antisaccades, activity was observed in the PEF contralateral to the target around 110ms after the target, and in the PEF ipsilateral to the target about 15ms later, around 135 ms post-target.
Conclusion: FEF and SEF activation occur prior to PEF activity during saccades, and may thus reflect not only execution but preparation of saccades. A shift in activity from the contralateral to ipsilateral hemisphere consistent with the vector inversion (sensorimotor transformation) required for antisaccades was observed in PEF rather than FEF after target presentation.
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