Systematic changes in the perceived posture of the wrist and elbow during formation of a phantom hand and arm

Our previous study showed that a fully flexed or extended hand became perceived as an extended or flexed 'phantom' hand as ischemic anesthesia progressed (Inui et al. in J Physiol 589:5775-5784, 2011). Here, we examined what happened if the hand was held in the midposition before and during the anesthesia. Twenty healthy participants reported the perceived postures of their right wrist and elbow during an ischemic block of the right upper arm using the left hand and arm. If the actual arm and hand were fully extended, then the perceived position of the elbow and wrist moved toward flexion. Conversely, if they were fully flexed, then the perceived position of the joints moved toward extension. However, when the hand was held in the midposition before and during the anesthesia, the position of the wrist was perceived to be in the same position. Hence, the fully flexed or extended position of a limb was essential for systematic changes in the perceived posture of the limb during the anesthesia. Because the start of these changes occurred as somatosensory inputs were declining, the changes depended on the fading inputs from strongly stretched muscle and skin during the anesthesia.