Perceptual Encoding of Self-Motion Duration in Human Posterior Parietal Cortex

It has been demonstrated previously that repetitive transcranial magnetic stimulation (rTMS) to right or left posterior parietal cortex (PPC) disrupts perceptual encoding of whole-body displacement during an angular path integration task using only vestibular cues for its completion. The effects of rTMS applied to right PPC (and left motor cortex as a control) during a vestibular-cued motion-reproduction task (i.e., not requiring path integration) were investigated in 5 subjects. Specifically, subjects were rotated in the dark on a motorized Barany chair with raised cosine velocities of durations 1, 2, and 3 s and peak 30 degrees, 60 degrees, 90 degrees, and 120 degrees/s. Subjects were required to actively reproduce the motion profile after every rotation with a chair-bound joystick. It was found that rTMS applied to the right PPC during the passive (encoding) stimulus phase had no effect on angular velocity reproduction when compared to control (motor-cortex rTMS). In contrast, motion-duration reproduction was significantly worse with right PPC (versus control motor cortex) rTMS. The results imply that vestibular-derived cues of motion duration, but not velocity, are encoded in human PPC. It was inferred from these and previous data that human PPC is involved in human path integration and motion-duration perception, but not angular velocity self-motion perception.