The various forms of sensorimotor plasticity following limb amputation and their link with rehabilitation strategies

What you feel is not always what you've got. Jean Lhermitte (1877-1959) and the phantom limb phenomenon

Jean Lhermitte (1877-1959), the French neurologist and psychiatrist, is most often associated with the sign he described in three patients with multiple sclerosis, back in 1927. In 1937, Lhermitte analytically studied a series of 28 amputees experiencing phantom limb sensations further to amputations dating between 1891 and 1934. After having described the main clinical characteristics of this unpublished series, we will detail the ideas advanced by Jean Lhermitte regarding the phenomenon of the phantom limb. Lhermitte will use these observations to develop conceptions of consciousness and the body schema encompassing very modern resonances.

Stable Cortical Body Maps Before and After Arm Amputation

Neuroscientists have long debated the adult brain's capacity to reorganize itself in response to injury. A driving model for studying plasticity has been limb amputation. For decades, it was believed that amputation triggers large-scale reorganization of cortical body resources. However, these studies have relied on cross-sectional observations post-amputation, without directly tracking neural changes. Here, we longitudinally followed adult patients with planned arm amputations and measured hand and face representations, before and after amputation. By interrogating the representational structure elicited from movements of the hand (pre-amputation) and phantom hand (post-amputation), we demonstrate that hand representation is unaltered. Further, we observed no evidence for lower face (lip) reorganization into the deprived hand region. Collectively, our findings provide direct and decisive evidence that amputation does not trigger large-scale cortical reorganization.

How Does the Central Nervous System for Posture and Locomotion Cope With Damage-Induced Neural Asymmetry?

In most vertebrates, posture and locomotion are achieved by a biomechanical apparatus whose effectors are symmetrically positioned around the main body axis. Logically, motor commands to these effectors are intrinsically adapted to such anatomical symmetry, and the underlying sensory-motor neural networks are correspondingly arranged during central nervous system (CNS) development. However, many developmental and/or life accidents may alter such neural organization and acutely generate asymmetries in motor operation that are often at least partially compensated for over time. First, we briefly present the basic sensory-motor organization of posturo-locomotor networks in vertebrates. Next, we review some aspects of neural plasticity that is implemented in response to unilateral central injury or asymmetrical sensory deprivation in order to substantially restore symmetry in the control of posturo-locomotor functions. Data are finally discussed in the context of CNS structure-function relationship.