Cerebral Cortex Advance Access originally published online on December 26, 2006
Cerebral Cortex 2007 17(10):2364-2374; doi:10.1093/cercor/bhl145
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Oscillatory Activity in Human Parietal and Occipital Cortex Shows Hemispheric Lateralization and Memory Effects in a Delayed Double-Step Saccade Task
1 Nijmegen Institute for Cognition and Information, 2 F.C. Donders Centre for Cognitive Neuroimaging, 3 Department of Biophysics, Radboud University Nijmegen, NL-6500 HE Nijmegen, The Netherlands
Address correspondence to W. P. Medendorp, PhD, Nijmegen Institute for Cognition and Information, Radboud University Nijmegen, PO Box 9104, NL-6500 HE Nijmegen, The Netherlands. Email: p.medendorp{at}nici.ru.nl.
We applied magnetoencephalography (MEG) to record oscillatory brain activity from human subjects engaged in planning a double-step saccade. In the experiments, subjects (n = 8) remembered the locations of 2 sequentially flashed targets (each followed by a 2-s delay), presented in either the left or right visual hemifield, and then made saccades to the 2 locations in sequence. We examined changes in spectral power in relation to target location (left or right) and memory load (one or two targets), excluding error trials based on concurrent eye tracking. During the delay period following the first target, power in the alpha (8–12 Hz) and beta (13–25 Hz) bands was significantly suppressed in the hemisphere contralateral to the target. When the second target was presented, there was a further suppression in the alpha- and beta-band power over both hemispheres. In this period, the same sensors also showed contralateral power enhancements in the gamma band (60–90 Hz), most significantly prior to the initiation of the saccades. Adaptive spatial filtering techniques localized the neural sources of the directionally selective power changes in parieto-occipital areas. These results provide further support for a topographic organization for delayed saccades in human parietal and occipital cortex.
Key Words: human • MEG • oscillations • parietal cortex • saccade • sensorimotor • spatial memory
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