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John de Grosbois, Frank Colino, Olav Krigolson, Matthew Heath, Gordon Binsted; EEG microstates during visually guided reaching. Journal of Vision 2010;10(7):1068. doi: 10.1167/10.7.1068.
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The notion that vision's importance in controlling goal-directed reaching movements has been experimentally validated (Woodworth, 1899). Functional MRI and rTMS work has subsequently confirmed that the posterior parietal cortex (PPC) are important for the control of visually guided movements (Culham and Kanwisher, 2001, Desmurget et al, 1999). The temporal resolution is inappropriate to study the cortical dynamics of reaching movements. Therefore, this investigation examined the activation dynamics of movement planning and control as measured by electroencephalography (EEG). Participants completed reaching movements during full-vision (FV), no-vision-delayed (NV) or open-loop (OL). Event-related potential analysis segmented with respect to peak velocity (PV) yielded differences in visual and motor areas following PV. To generate an overall evaluation of the activation across time, ERP waveforms were submitted to a space-oriented field clustering approach (Tunik et al, 2008) to determine epochs of semi-stable field configurations (i.e. microstates) throughout the planning/control of reaches. The results of this micro-state analysis showed that regardless of visual condition, the planning and initiation of movement is characterized by two state transitions: an activation pattern dominated by increasing primary-visual and motor activation (FCz, Oz). NV remained in this early movement state and did not enter any control-based state. During FV, activation shifted following PV to an activation consistent with dorsal (contralateral PPC, frontal and 1o visual areas) guidance of movement. OL transitioned into a bilateral temporal (presumably memory-guided) mode of control that did not exhibit primary visual activation. This had been expected of NV. Thus, even though previous fMRI studies have correctly identified important structures for the control of movement across different visual conditions, they have lacked the temporal resolution to elucidate the pattern of functioning across visually guided reaching movements.
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