MT+/V5 activation without conscious motion perception: A high-field fMRI study

While activity of MT+/V5 neurons is believed to be necessary for the conscious perception of visual motion, whether neural activity in MT+/V5 is a sufficient condition for the conscious perception of motion in vision still remains unanswered. A high-field (3.0 Tesla) functional magnetic resonance imaging (fMRI) study was designed and performed to answer this specific question. Eleven healthy subjects viewed a checkerboard pattern stimulus reversed in contrast at 0.2, 12, 30, and 60 Hz while being probed for activation in MT+/V5. At 0.2 Hz, all viewers perceived pattern-reversal which was stationary in position. However, at 12, 30, and 60 Hz, many subjects perceived apparent motion (e.g., vertical and horizontal flows) in the square pattern. At 12 and 30 Hz reversals, MT+/V5 was activated in all subjects (11/11). Nevertheless, three out of eleven (3/11) subjects denied motion perception in these conditions. At 60 Hz reversal, as many as seven out of eleven (7/11) subjects failed to see motion but activation in MT+/V5 was found in the majority (5/7) of the subjects. The results demonstrated that significant MT+/V5 activation occurs without accompanying subjective awareness of seeing motion in an apparent-motion stimulus, indicating that neural activity in MT+/V5 does not represent a sufficient condition for conscious perception of motion in vision.