Cerebral processing of spontaneous reversals of the rotating Necker cube.

The cerebral processing of spontaneous perceptive reversals of the rotating Necker cube was studied in humans by combined functional MRI and electroencephalography. These reversals prefer certain positions of the Necker cube and can be studied without external reference of the perception. Functional MRI revealed six bilaterally active regions in the visual, parietal, and premotor cortex. A new method determined phase-locked electroencephalography-activations in the regions of interest and showed a significant stimulus-locked activity that started in the left Brodmann area 18. This activity started 38 ms after passing the symmetric position of the Necker cube and spread along the dorsal stream. We suggest that a further portion of the event-related potential signal reflects additional top-down processing, dependent on the position of the Necker cube.