Human MST Research Articles

Retinotopy and Functional Subdivision of Human Areas MT and MST

We performed a series of functional magnetic resonance imaging experiments to divide the human MT+ complex into subregions that may be identified as homologs to a pair of macaque motion-responsive visual areas: the middle temporal area (MT) and the medial superior temporal area (MST). Using stimuli designed to tease apart differences in retinotopic organization and receptive field size, we established a double dissociation between two distinct MT+ subregions in 8 of the 10 hemispheres studied. The first subregion exhibited retinotopic organization but did not respond to peripheral ipsilateral stimulation, indicative of smaller receptive fields. Conversely, the second subregion within MT+ did not demonstrate retinotopic organization but did respond to peripheral stimuli in both the ipsilateral and contralateral visual hemifields, indicative of larger receptive fields. We tentatively identify these subregions as the human homologues of macaque MT and MST, respectively. Putative human MT and MST were typically located on the posterior/ventral and anterior/dorsal banks of a dorsal/posterior limb of the inferior temporal sulcus, similar to their relative positions in the macaque superior temporal sulcus.

The constructive nature of vision: direct evidence from functional magnetic resonance imaging studies of apparent motion and motion imagery.

Echoplanar functional magnetic resonance imaging was used to monitor activation changes of brain areas while subjects viewed apparent motion stimuli and while they were engaged in motion imagery. Human cortical areas MT (V5) and MST were the first areas of the 'dorsal' processing stream which responded with a clear increase in signal intensity to apparent motion stimuli as compared with flickering control conditions. Apparent motion of figures defined by illusory contours evoked greater activation in V2 and MT/MST than appropriate control conditions. Several areas of the dorsal pathway (V3A, MT/MST, areas in the inferior and superior parietal lobule) as well as prefrontal areas including FEF and BA 9/46 responded strongly when subjects merely imagined moving stimuli which they had seen several seconds before. The activation during motion imagery increased with the synaptic distance of an area from V1 along the dorsal processing stream. Area MT/MST was selectively activated during motion imagery but not during a static imagery control condition. The comparison between the results obtained with objective motion, apparent motion and imagined motion provides further insights into a complex cortical network of motion-sensitive areas driven by bottom-up and top-down neural processes.

Effect of Eye Movements on the Magnitude of fMRI Responses in Extrastriate Cortex during Visual Motion Perception

We have studied the effects of eye movements on the functional magnetic resonance imaging (fMRI) response during global dot motion in extrastriate temporo-occipital cortex. Susceptibility-based functional magnetic resonance, applying gradient-recalled echo-planar imaging (EPI) sequences, was conducted, in 12 volunteers who viewed episodes of moving dots. Anatomical and functional images were recorded with a 1.5 T Siemens Magnetom Vision (TR 5000 ms, TE 70 ms, flip angle 90°, FOV 250 mm, matrix 112 × 128, twelve 4-mm slices parallel to ac — pc plane, ranging from z=-14 – 34 mm). Sagittal T1-weighted images were acquired to determine the ac — pc plane and important anatomical landmarks. Eye movements were monitored with the use of MR-compatible EOG electrodes. Stimuli were back-projected onto a translucent screen and viewed through prisms. The four test conditions were: fronto-parallel motion, during fixation and during target pursuit; expansion-contraction motion, also during fixation and during pursuit. Pixelwise t-tests were performed on functional series recorded during rest and stimulation periods (50 s each) to identify significantly activated voxels. Planes −8 to +8 mm around the ac — pc plane and 20 – 28 mm superior to ac — pc were activated most by visual motion. In addition to primary visual cortical areas, a ventral area in the temporo-occipital cortex (human MT) responded well to both types of visual motion and these responses were enhanced by eye movements. Human MST, located dorsal of MT, showed activation by visual motion during fixation. Its response was also enhanced by pursuit.