Wide-field retinotopy distinguish subregions of the human MT+ by functional magnetic resonance imaging

Abstract

In humans, In humans, functional imaging studies have demonstrated a homologue of the macaque motion complex, MT+ suggested to contain both middle temporal (MT) and medial superior temporal (MST), in the ascending limb of the inferior temporal sulcus. Two of the most well studied areas are MT and MST. Macaque area MST has been shown to have considerably larger receptive fields than area MT. The receptive fields of MT cells typically extend only a few degrees into the ipsilateral visual field, while area MST neurons have receptive fields that extend well into the ipsilateral visual field. However, for human most studies thus far have only concentrated on the center and/or peri-center of the visual field. We used functional magnetic resonance imaging (fMRI) distinguish putative human areas MST from MT+ by wide-view stimuli. Random dots stimuli placed in the four steps (0∼8°, 8∼16°, 16∼32°, 32∼64° eccentricity) field, produced a large cluster of functional activation in our subjects consistent with previous reports of human area MT. Wide-field random dots stimuli limited to the peripheral retina produced activation only in an anterior subsection of the MT+ complex, likely corresponding to putative MST [Fig. 1A, B]. We also investigated the retinotopy characteristic of MT+ [Fig. 1C, D]. The retinotopy stimulus was a 60° diameter circular aperture filled with white dots on a black background. At any given time, the dots within a 45° wedge of the aperture moved inward/outward from fixation as in the MT+ localizer stimulus.