Real and imaginary rotary motion processing: functional parcellation of the human parietal lobe revealed by fMRI.

Functional magnetic resonance imaging was performed in 16 healthy subjects while they undertook orientation discrimination tasks of real rotating and mentally rotating alphanumeric characters. Perception of rotating and stationary abstract characters was also performed. Mental rotation and the perception of alphanumeric characters undergoing real rotation activated equivalent cortical areas, in keeping with the analogue hypothesis of mental rotation. In addition, areas along the dorsal stream, including the V5/middle temporal complex and the intraparietal sulcus (IPS), were activated during both the real and imaginary rotary conditions. Within the parietal lobe there were areas of convergence (i.e., recruited by all three motion conditions) and areas of divergence (i.e., selectively activated by a particular condition). Tasks requiring canonical-mirror orientation discrimination revealed involvement of neural substrates localized to the ventrolateral bank of the IPS. Tasks in which this judgment was not performed and during which the subject viewed rotary motion of abstract stimuli recruited activity in the medial bank of the IPS. These results indicate subspecialization of the human posterior parietal lobe according to function.