Distinguishing subregions of the human MT plus complex using visual fieldsand pursuit eye movements

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 contr alateral visual field, MST dorsal (MSTd) receptive fields extend well into the ipsilateral visual field. Additionally, macaque MST has been shown to r eceive extraretinal smooth-pursuit eye-movement signals, whereas MT does no t. We used functional magnetic resonance imaging (fMRI) and the neural prop erties that had been observed in monkeys to distinguish putative human area s MT from MST. Optic flow stimuli placed in the full field, or contralatera l field only, produced a large cluster of functional activation in our subj ects consistent with previous reports of human area MT+. Ipsilateral optic flow stimuli limited to the peripheral retina produced activation only in a n anterior subsection of the MT+ complex, likely corresponding to putative MSTd. During visual pursuit of a single target, a large portion of the MTcomplex was activated. However, during nonvisual pursuit, only the anterola teral portion of the MT+ complex was activated. This subsection of the MTcluster could correspond to putative MSTl (lateral). In summary, we observe d three distinct subregions of the human MT+ complex that were arranged in a manner similar to that seen in the monkey.