Patterns of cerebral activation while mental images are rotated and changed in size.

Event-related brain potentials were recorded while subjects performed either a rotation or a size scaling transformation of a mental image. Images had to be rotated 0 degrees, 60 degrees, or 120 degrees or their size had to be enlarged by factors of 1:1, 1:3, or 1:5. Both tasks were accompanied by pronounced negative slow potentials, which extended over several seconds. The relative maximum of these shifts emerged at central to occipital leads. Over the occipital cortex, the negative potential had a similar amplitude level in all conditions and both tasks. However, at parietal and central areas, the negative slow wave changed in relation to the difficulty of the task. The amplitude increased with increasing rotation demands and if the scaling operation required an exact computation of the coordinates of the image. None of these effects could be attributed to an inverse change of P300.