Cortical representations of phantom movements in lower limb amputees

Abstract

Understanding how sensorimotor cortex (SMC) organization relates to limb loss has major clinical implications, as cortical activity associated with phantom hand movements has been shown to predict phantom pain reports. Critically, earlier studies have largely focused on upper limb amputees; far less is known regarding SMC activity in lower limb amputees, despite the fact that this population comprises the majority of major limb loss cases. We aimed to characterize BOLD fMRI responses associated with phantom and sound limb movements to test the hypothesis that SMC organization is preserved in individuals with lower limb loss. Individuals with unilateral or bilateral lower limb loss underwent fMRI scans as they performed simple movements of their sound or phantom limbs. We observed that voluntary movements of the sound and phantom ankles were associated with BOLD signal changes in medial and superior portions of the precentral and postcentral gyri. In both hemispheres, contralateral limb movements were associated with greater signal changes compared to ipsilateral limb movements. Hand and mouth movements were associated with distinct activation patterns localized to more lateral SMC regions. We additionally tested whether activations associated with phantom movements related to self-report assessments indexing phantom pain experiences, nonpainful phantom sensations and phantom movement capabilities. We found that responses during phantom ankle movements did not correlate with any of the composite phantom limb indices in our sample. Our collective results reveal that SMC representations of the amputated limb persist and that traditional somatotopic organization is generally preserved in individuals suffering from lower limb loss. K E Y W O R D SfMRI, legs, limb loss, phantom pain, transfemoral, transtibial | INTRODUCTIONMajor limb loss can result in extensive perceptual and behavioural changes, including impoverished or altered sensory functions and reductions in motor activities. Following major limb loss, individuals also often continue to perceive their amputated limb, with a majority experiencing phantom limb pain (Dijkstra et al., 2002). Given its detrimental impact on

Cortical activation during imagined walking for people with lower limb loss: a pilot study

“…The systematic review by Hamacher et al (2015) did not include any studies evaluating people with LLA, so direct comparison across studies on people with LLA is not possible. Wang et al (2021) found sensorimotor cortex organization is preserved in people with LLA, our study also demonstrated increased activation on the medial surface of the primary motor and sensory cortices that corresponds to lower limb topographical representation. Alterations in the primary motor homunculus of the amputated lower limb is another area for further exploration for imagined walking.…”