Distinguishing Subregions of the Human MT+ Complex Using Visual Fields and Pursuit Eye Movements

1 Graduate Program in Neuroscience, Siebens-Drake Research Institute, University of Western Ontario, London, Ontario N6G 2V4; 2 Department of Psychology, University of Western Ontario, London, Ontario N6A 5C2; 3 Advanced Imaging Labs, The John P. Robarts Research Institute, London, Ontario N6A 5K8; 4 Department of Physiology, University of Western Ontario, London, Ontario N6A 5C1, Canada; and 5 Department of Physiology, Erasmus Universiteit Rotterdam, 3000 DR Rotterdam, The Netherlands Dukelow, Sean P., Joseph F. X. DeSouza, Jody C. Culham, Albert V. van den Berg, Ravi S. Menon, and Tutis Vilis. Distinguishing Subregions of the Human MT+ Complex Using Visual Fields and Pursuit Eye Movements. J. Neurophysiol. 86: 1991-2000, 2001. 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. In the macaque monkey, motion-sensitive areas MT and MST are adjacent in the superior temporal sulcus. Electrophysiological research has demonstrated that while MT receptive fields primarily encode the contralateral visual field, MST dorsal (MSTd) receptive fields extend well into the ipsilateral visual field. Additionally, macaque MST has been shown to receive extraretinal smooth-pursuit eye-movement signals, whereas MT does not. We used functional magnetic resonance imaging (fMRI) and the neural properties that had been observed in monkeys to distinguish putative human areas MT from MST. Optic flow stimuli placed in the full field, or contralateral field only, produced a large cluster of functional activation in our subjects consistent with previous reports of human area MT+. Ipsilateral optic flow stimuli limited to the peripheral retina produced activation only in an anterior subsection of the MT+ complex, likely corresponding to putative MSTd. During visual pursuit of a single target, a large portion of the MT+ complex was activated. However, during nonvisual pursuit, only the anterolateral portion of the MT+ complex was activated. This subsection of the MT+ cluster could correspond to putative MSTl (lateral). In summary, we observed three distinct subregions of the human MT+ complex that were arranged in a manner similar to that seen in the monkey.