Neuroplasticity in People Affected by Major Upper Limb Amputation: a Transcranial Magnetic Stimulation study

Major upper limb amputations (mULAs) have disastrous consequences for amputees' life, in terms of mental, physical, and social well-being. Despite the advances in medical technology and computer software applied to medicine, people affected by mULA continue to use, as a standard of care, prosthetic technologies developed almost half a century ago, with high rates of rejection and low satisfaction rates. Targeted muscle reinnervation (TMR) is a new surgical approach that is revolutionizing the field of prosthetics. Studies are ongoing to assess the long-term outcomes and to maximize the potential of this novel approach. The study of neuroplasticity (i.e. how the nervous system changes) after limb amputations can offer fundamental insights for the challenge of improving surgical and rehabilitation outcomes and prosthetic control. The aims of this study were: studying hemispheric differences in corticospinal excitability in a population of subjects with chronic (>1 year) mULA using active control prosthesis; - evaluating in the same population the effects of "acute" neuromodulatory interventions (continuous Theta Burst Stimulation (cTBS) and Paired Associative Stimulation (PAS-10)) in terms of inhibition of corticospinal excitability; - moreover, we wanted to study, for the first time in literature, the neuroplastic changes occurring at the primary motor cortex before and after TMR surgery. We found that basal corticospinal excitability, assessed through Motor Evoked Potentials (MEPs) peak-to-peak amplitude was significantly higher for the brain hemisphere contralateral to the amputation side (p <0.002). cTBS (n = 12) induced a significant inhibition of MEPs amplitude 5 minutes after stimulation (p = 0.02), present 10 minutes after stimulation (p = 0.001). PAS-10 (n = 6) did not induce significant changes in MEPs amplitude. Lastly, we describe in detail the changes in corticospinal excitability and cortical motor maps in one subject who underwent TMR surgery.