Eye-hand reaching movements are controlled by a fronto-parietal network with distinct foci for the different functional subcomponents

Introduction: Reaching movements are combined of different subcomponents consisting of eye-hand movements towards a spatially located target. Within a parieto-premotor network specialized cortical areas seem to subserve differenzial functions concerning the control of the motor effector and the position in space. Besides the identification of commonalities, we also wanted to study the differenzial contribution of specialized areas that included frontal and parietal areas. Tasks consisted of various performances of saccades, reaching movements, and additionally covert shifts of attention towards a target presented in horizontal positions in the left and right visual field.

Methods: We examined 16 volunteers at 3T. Each task consisted of pure preparation or the actual performance of visually guided saccades, reaching movements or simply shifts of covert attention towards a target presented on a screen in front of the scanner. The target, a laser point, was presented in different horizontal positions. During the attention task the volunteer kept central fixation and just shifted attention to the peripherally presented target. Saccade performance and central fixation was controlled with an MR-compatible infrared-oculography during the scan. Activation was determined by individual and group analysis using SPM 2 and second level analysis.

Results: Eye movements activated the saccade related areas i.e. frontal and supplementary eye field, areas in the intraparietal sulcus and the posterior parietal lobe. Reaching movements activated areas including the primary motor cortex, the supplementary motor area, parietal lobe and also the FEF, with additional specific activation of premotor cortex and an area that could correspond to left V6A. There was a substantial overlap of activation with areas activated by covert shifts of attention. Signal intensity analysis in individual dedicated areas for preparing eye or hand movements revealed differenzial peak activations. A region corresponding to the AIP was related to hand movements. In the parietal lobe, we could demonstrate distinct main foci for the hand and the saccade component and a dorso-occipital focus for calculation regarding visual space.

Conclusion: Apart from the activation of a broadly overlapping network during isolated or combined eye-hand reaching movements, we could demonstrate specific activations with respect to the different subcomponents during reaching movements in space.