Selective disturbance of mental rotation by cortical stimulation.

In order to plan activity, people must imagine the spatial consequences of potential actions. Two classes of mental spatial transformation can be distinguished: Object-based spatial transformations are imagined movements of objects, such as mental rotation. Egocentric perspective transformations are imagined changes in one's viewpoint, such as imagining one's self in the position of another person. Here we report a case in which electrical stimulation of the right parietal cortex selectively interfered with performance of a mental rotation task. Interference was selective to this stimulation site, and was task specific. Performance of the perspective transformation task, and a control for visual encoding and responding, were unimpaired by stimulation. This marks the first instance of the use of direct cortical stimulation to investigate mental spatial transformations.