Formation of Phantom Limbs Following Ischemic Nerve Block

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The brain needs body image to plan movement. We use ischemic anesthesia of a limb to study the mechanisms of changes in body image (Sects. 2.1, 2.3, and 2.5). First, if the fingers, wrist, elbow, knee, and ankle are extended before and during anesthesia, the perceived phantom limbs are flexed at the joints and vice versa. However, when the hand is held in the mid-position before and during the anesthesia, the position of the wrist is perceived to be in the same position (Sect. 2.3). 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. In addition, if the actual wrist was fully extended while the actual elbow was fully flexed, then the perceived position of the wrist moved toward flexion and that of the elbow moved toward extension and vice versa (Sect. 2.4). Following the loss of the afferent signal coming from the main muscles acting at the two joints, the two perceived postures moved toward the opposite direction independently. Second, perceived hand size increases by 34 ± 4 % (mean ±95 % confidence interval) as anesthesia develops (Sect. 2.6). Third, the start of these perceptual changes occurs when input from large-diameter sensory nerve fibers is declining (Sect. 2.2). Fourth, at the end of the ischemic block, when participants are allowed to see their foot, its perceived position reverts to that indicated by them earlier (Sect. 2.5).