Brain, Vol 121, Issue 1 143-157, Copyright © 1998 by Oxford University Press
L Cornette, P Dupont, W Spileers, S Sunaert, J Michiels, P Van Hecke, L Mortelmans and GA Orban
In this PET study, we have investigated the human brain activity evoked by
a visual motion paradigm commonly used to measure motion-related visual
evoked potentials (VEPs). Because standard PET activation studies have been
performed with motion along four axes, we first determined the pattern of
brain activation when motion was restricted to a single axis. Motion back
and forward along a single horizontal axis compared with a static condition
revealed weak differential activations in the cuneus and the parietal
cortex. Human area MT/V5 (middle temporal area) was hardly activated at all
in this subtraction. Additional functional MRI experiments proved that
MT/V5 activity is significantly higher for motion along four axes than for
motion along a single axis. Secondly, 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 compared both conditions with a contrast- modulated static or
continuous motion condition. Subtraction of the static random dot pattern
condition from the single-axis motion reversal condition, both
contrast-modulated, revealed three significant activations: the anterior
parieto-occipital sulcus, the lateral sulcus and the anterior claustrum.
Additional analysis showed that these activations were not due to motion
appearance 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
response to the reversal transient per se, we used a conjunction analysis,
which suggests that activity in human MT/V5, the cuneus and a parietal
insular region could underlie the motion reversal VEP in our experiments.
Subtraction of the static random dot pattern condition from the single-axis
motion onset condition, both contrast-modulated, revealed a single
significant activation in the posterior cingulate cortex. Although the
significance of this activation is unclear, it adds further evidence for
the visual function of this region.
ARTICLES
Human cerebral activity evoked by motion reversal and motion onset. A PET study
Laboratorium voor Neuro- en Psychofysiologie, KU Leuven, Medical School, Belgium.
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