Progressive changes in cutaneous trigger zones for sensation referred to a phantom hand: a case report and review with implications for cortical reorganization

Abstract

The dominant model of cortical plasticity induced by peripheral denervation suggests that a physiologically-reorganized cortical area can acquire new perceptual meaning, including a change in the peripheral referral of sensation. An alternative view is that such an area may retain its former perceptual significance, even though it becomes responsive to new peripheral inputs. To examine evidence related to this issue, a clinical case is presented documenting the time course of changes in phantom limb sensation in a patient with accidental amputation of a hand. About 24 h after injury, a vivid phantom hand was present; tactile stimulation revealed cutaneous trigger zones on the arm, stimulation of which elicited sensation referred to specific fingers of the phantom. While the phantom hand percept remained fairly stable over time, the trigger zones expanded progressively in size during the next 1-8 weeks but had contracted and changed location considerably about one year later. At all times studied, the trigger zones were topographically related to specific fingers and other parts of the phantom hand. The implications of these and other recent clinical findings for cortical reorganization are discussed, and the following tentative conclusions are drawn. (1) A phantom percept is mediated by central neural networks which remain functionally intact after amputation. (2) Cutaneous trigger zones mapped in humans correspond to novel receptive fields of cortical neurons mapped in animals following peripheral denervation. (3) Cortical reorganization induced by denervation does not produce a major change in perceptual meaning or peripheral reference. In the present case, stimulation of new trigger zones (receptive fields) on the patient's arm presumably activated a reorganized cortical hand area but evoked sensation still referred to the (now missing) hand. Hence, physiological cortical remapping is not necessarily accompanied by functional respecification.

• Key Words: Phantom Limbs, Referred Sensation, Cutaneous Trigger Zones, Somatosensory Cortex, Cortical Reorganization, Plasticity