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Abstract:
Human fMRI studies of binocular rivalry and other bistable phenomena suggest that a network of frontal and parietal areas, predominantly in the right hemisphere, is particularly involved during switches between the two conflicting percepts. However, these studies do not provide information about causality, i.e. whether fMRI activity is a consequence or a cause of the perceptual change. In the current study we localized areas that were activated
during perceptual switches in individual subjects using fMRI. We then tested the effect of disturbing neural processing in two distinct parietal regions along the ventral-dorsal axis in both hemispheres using 2 Hz repetitive transcranial magnetic stimulation (TMS). Our results show that on the group level, TMS over the right intraparietal sulcus (IPS) prolonged the periods of stable percepts. In individual subjects, the IPS in the hemisphere with higher fMRI activation also showed a stronger TMS effect, as reflected in the positive correlation between
the lateralization of TMS effects and that of fMRI activations. Our results thus demonstrate a causal, de-stabilizing effect of the IPS on perceptual continuity and provide a direct link between correlational and causal measures of cortical function during conscious perception.
