ACTIVATION OF VISUOMOTOR SYSTEMS DURING VISUALLY GUIDED MOVEMENTS - AFUNCTIONAL MRI STUDY

The dorsal stream is a dominant visuomotor pathway that connects the s triate and extrastriate cortices to posterior parietal areas. In turn, the posterior parietal areas send projections to the frontal primary motor and premotor areas. This cortical pathway is hypothesized to be involved in the transformation of a visual input into the appropriate motor output. In this study we used functional magnetic resonance imag ing (fMRI) of the entire brain to determine the patterns of activation that occurred while subjects performed a visually guided motor task. In nine human subjects, fMRI data were acquired on a 4-T whole-body MR system equipped with a head gradient coil and a birdcage RF coil usin g a T-2-weighted EPI sequence. Functional activation was determined f or three different tasks: (1) a visuomotor task consisting of moving a cursor on a screen with a joystick in relation to various targets, (2 ) a hand movement task consisting of moving the joystick without visua l input, and (3) a eye movement task consisting of moving the eyes alo ne without visual input. Blood oxygenation level-dependent (BOLD) cont rast-based activation maps of each subject were generated using period cross-correlation statistics. Subsequently, each subject's brain was normalized to Talairach coordinates, and the individual maps were comp ared on a pixel by pixel basis. Significantly activated pixels common to at least four out of six subjects were retained to construct the fi nal functional image. The pattern of activation during visually guided movements was consistent with the flow of information from striate an d extrastriate visual areas, to the posterior parietal complex, and th en to frontal motor areas. The extensive activation of this network an d the reproducibility among subjects is consistent with a role for the dorsal stream in transforming visual information into motor behavior. Also extensively activated were the medial and lateral cerebellar str uctures, implicating the cortico-ponto-cerebellar pathway in visually guided movements. Thalamic activation, particularly of the pulvinar, s uggests that this nucleus is an important subcortical target of the do rsal stream. (C) 1998 Academic Press.