Ipsilateral Motion Stimuli Dissociate MST from MT in Humans Using fMRI

Abstract:
Abstract: Neurons in Macaque area MT and adjacent area MSTd are responsive to motion stimuli. Electrophysiology has shown that MT receptive fields are typically located in the contralateral visual field whereas MSTd receptive fields are much larger and typically extend well into the ipsilateral visual field. We examined whether a similar segregation exists in humans on the basis of receptive field properties. Subjects were scanned at high resolution (1x1x2mm) using a 4 Tesla MRI scanner with a right occipital surface coil. Radial dot stimuli located in either the contralateral or ipsilateral visual field were presented 15 degrees from the vertical midline. Contralateral moving minus stationary dots revealed a significantly activated area consistent with that of human area MT+ complex at the junction of the Lateral Occipital and Inferior Temporal Sulci. Ipsilateral moving minus stationary dots revealed an area that was consistently located in the anterior portion of the MT+ complex, likely corresponding to human area MSTd. Subjects also performed pursuit eye tracking of a finger in complete darkness. Non-visual pursuit minus fixation revealed significant activation anterior to putative area MT. Thus, high- resolution fMRI allows visualisation of human homologues of monkey motion areas MT and MST.