Reciprocal interactions between the position sense representations of the two forearms.

Muscle spindle afferents are known to influence the conscious appreciation of limb position. If a limb muscle is mechanically vibrated while the limb is physically restrained from moving under the action of the resulting tonic vibration reflex, illusory motion of the limb will be experienced in the direction that would be associated with stretch of the vibrated muscle. Two experiments are presented that explore how grasping with the other hand the forearm of an arm whose biceps or triceps muscle is being vibrated affects the apparent position of the two arms. If the vibrated arm is grasped before the onset of vibration, then illusory motion of both arms is experienced during vibration. The magnitude of this apparent motion and displacement is less than that experienced when the vibrated arm is not held. If the vibrated arm is grasped after the onset of vibration and when illusory displacement is being experienced, then its apparent motion is suppressed and the grasping arm is correctly perceived as stationary. The existence of this reciprocal, position sense interaction between the two arms suggests that the conscious awareness of limb position is not dependent solely on afferent and efferent information about individual limbs in isolation, but potentially involves coordinating spatial information about the configuration of the entire body.