Functional analysis of human MT and related visual cortical areas using magnetic resonance imaging

Abstract

Using noninvasive functional magnetic resonance imaging (fMRI) technique, we analyzed the responses in human area MT with regard to visual motion, color, and luminance contrast sensitivity, and retinotopy. As in previous PET studies, we found that area MT responded selectively to moving (compared to stationary) stimuli. The location of human MT in the present fMRI results is consistent with that of MT in earlier PET and anatomical studies. In addition we found that area MT has a much higher contrast sensitivity than that in several other areas, including primary visual cortex (V1). Functional MRI half-amplitudes in V1 and MT occurred at approximately 15% and 1% luminance contrast, respectively. High sensitivity to contrast and motion in MT have been closely associated with magnocellular stream specialization in nonhuman primates. Human psychophysics indicates that visual motion appears to diminish when moving color-varying stimuli are equated in luminance. Electrophysiological results from macaque MT suggest that the human percept could be due to decreases in firing of area MT cells at equiluminance. We show here that fMRI activity in human MT does in fact decrease at and near individually measured equiluminance. Tests with visuotopically restricted stimuli in each hemifield produced spatial variations in fMRI activity consistent with retinotopy in human homologs of macaque areas V1, V2, V3, and VP. Such activity in area MT appeared much less retinotopic, as in macaque. However, it was possible to measure the interhemispheric spread of fMRI activity in human MT (half amplitude activation across the vertical meridian = approximately 15 degrees).

Cortical and cerebellar activation induced by reflexive and voluntary saccades

“…Functional imaging studies in humans have shown that the human homologue, area MT/V5, is also highly responsive to visual motion stimuli (Zeki et al 1991;Watson et al 1993;Tootell et al 1995). We found that MT/V5 was bilaterally more activated in the reXexive than in the voluntary saccade condition, although no real visual motion was present in either condition.…”

The relationship between MEG and fMRI

“…variation of Michelson contrast), showing that BOLD signal increases non-linearly with contrast (see also (Tootell et al, 1995)) whilst beta band power loss during stimulation was approximately equal regardless of visual contrast. This was in contrast to the visual gamma band response, which increased monotonically with stimulus contrast, (see also ).…”

Event perception: A mind-brain perspective.

“…(Tanaka, 1996). Regions in the dorsal stream corresponding to areas MT and MST in the monkey, dubbed "the MT complex" (MT +), selectively represent features of object and observer movement (Tootell, et al, 1995). Adjacent areas in the posterior superior temporal sulcus (pSTS) are selectively activated by nonrigid biological motion (Grossman, et al, 2000;Beauchamp, Lee, Haxby, & Martin, 2003).…”