Illusory arm movements activate cortical motor areas: A positron emission tomography study

Vibration at similar to 70 Hz on the biceps tendon elicits a vivid illusory arm extension. Nobody has examined which areas in the brain are activated when subjects perceive this kinesthetic illusion. The illusion was hypothes ized to originate from activations of somatosensory areas normally engaged in kinesthesia. The locations of the microstructurally defined cytoarchitec tonic areas of the primary motor (4a and 4p) and primary somatosensory cort ex (3a, 3b, and 1)were obtained from population maps of these areas in stan dard anatomical format. The regional cerebral blood flow (rCBF) was measure d with O-15-butanol and positron emission tomography in nine subjects. The left biceps tendon was vibrated at 10 Hz (LOW), at 70 or 80 Wt (ILLUSION), or at 220 or 240 Hz (HIGH). A REST condition with eyes closed was included in addition. Only the 70 and 80 Hz vibrations elicited strong illusory arm extensions in all subjects without any electromyographic activity in the ar m muscles. When the rCBF of the ILLUSION condition was contrasted to the LO W and HIGH conditions, we found two clusters of activations, one in the sup plementary motor area (SMA) extending into the caudal cingulate motor area (CMAc) and the other in area 4a extending into the dorsal premotor cortex ( PMd) and area 4p. When LOW, HIGH, and ILLUSION were contrasted to REST, giv ing the main effect of vibration, areas 4p, 3b, and 1, the frontal and pari etal operculum, and the insular cortex were activated. Thus, with the excep tion of area 4p, the effects of vibration and illusion were associated with disparate cortical areas. This indicates that the SMA, CMAc, PMd, and area 4a were activated associated with the kinesthetic illusion. Thus, against our expectations, motor areas rather than somatosensory areas seem to conve y the illusion of limb movement.