HUMAN CEREBRAL-ACTIVITY EVOKED BY MOTION REVERSAL AND MOTION ONSET - A PET STUDY

In this PET study, we have investigated the human brain activity evoke d by a visual motion paradigm commonly used to measure motion-related visual evoked potentials (VEPs). Because standard PET activation studi es have been performed with motion along four axes, we first determine d the pattern of brain activation when motion was restricted to a sing le axis. Motion back and forward along a single horizontal axis compar ed with a static condition revealed weak differential activations in t he cuneus and the parietal cortex. Human area MT/V5 (middle temporal a rea) was hardly activated at all in this subtraction. Additional funct ional MRI experiments proved that MT/V5 activity is significantly high er for motion along four axes than for motion along a single axis. Sec ondly we attempted to isolate the pattern of brain activity related to the reversal of motion direction and to the onset of motion, i.e. two transient motion components commonly used in measuring motion-related VEPs. To that end, we added a continuous linear contrast modulation, that reached maximum contrast at reversal or onset of motion, and comp ared both conditions with a cingulate cortex. Although the significanc e of this activation is unclear it adds further evidence for the visua l function of this region. contrast-modulated static or continuous mot ion condition. Subtraction of the static random dot pattern condition from the single-axis motion reversal condition, both contrast-modulate d revealed three significant activations: the anterior parieto-occipit al sulcus, the lateral sulcus and the anterior claustrum. Additional a nalysis showed that these activations were not due to motion appearanc e or disappearance, but were due to the combination of motion reversal and contrast modulation. Hence, these activations do not reflect the motion reversal transient per se. In order to isolate a metabolic resp onse to the reversal transient per se, we used a conjunction analysis, which suggests that activity in human MT/V5, the cuneus and a parieta l insular region could underlie the motion reversal VEP in our experim ents. Subtraction of the static random dot pattern conditions from the single-axis motion onset condition, both contrast-modulated revealed a single significant activation in the posterior cingulate cortex. Alt hough the significance of this activation is unclear, it adds further evidence for the visual function of this region.