Brain (re)organisation following amputation: Implications for phantom limb pain

Abstract

Following arm amputation the region that represented the missing hand in primary somatosensory cortex (S1) becomes deprived of its primary input, resulting in changed boundaries of the S1 body map. This remapping process has been termed ‘reorganisation’ and has been attributed to multiple mechanisms, including increased expression of previously masked inputs. In a maladaptive plasticity model, such reorganisation has been associated with phantom limb pain (PLP). Brain activity associated with phantom hand movements is also correlated with PLP, suggesting that preserved limb functional representation may serve as a complementary process. Here we review some of the most recent evidence for the potential drivers and consequences of brain (re)organisation following amputation, based on human neuroimaging. We emphasise other perceptual and behavioural factors consequential to arm amputation, such as non-painful phantom sensations, perceived limb ownership, intact hand compensatory behaviour or prosthesis use, which have also been related to both cortical changes and PLP. We also discuss new findings based on interventions designed to alter the brain representation of the phantom limb, including augmented/virtual reality applications and brain computer interfaces. These studies point to a close interaction of sensory changes and alterations in brain regions involved in body representation, pain processing and motor control. Finally, we review recent evidence based on methodological advances such as high field neuroimaging and multivariate techniques that provide new opportunities to interrogate somatosensory representations in the missing hand cortical territory. Collectively, this research highlights the need to consider potential contributions of additional brain mechanisms, beyond S1 remapping, and the dynamic interplay of contextual factors with brain changes for understanding and alleviating PLP.

The Phantom Satiation Hypothesis of Bariatric Surgery

“…The field of neurology teaches us the contrary. Indeed, many amputees continue to feel the presence of their lost limb, a phenomenon described as phantom limb ( Ramachandran et al, 2009 ; Collins et al, 2018 ; Makin and Flor, 2020 ). Even though phantom pain syndromes have been first described 500 years ago ( Keil, 1990 ), the treatment of phantom limb syndromes has remained challenging up to this day ( Alviar et al, 2016 ).…”

Cortical representations of phantom movements in lower limb amputees

“…Due to the relative paucity of neuroimaging studies with lower limb amputees compared to upper limb amputees, it is unclear whether lower limb amputation results in SMC activity changes that are consistent with the patterns observed following upper limb amputation. A prominent hypothesis posits that SMC organization and function reflect limb‐use behaviours (Dempsey‐Jones et al., 2019; Makin, Cramer, et al., 2013; Makin & Flor, 2020), with deprived cortex responses in upper limb amputees mirroring residual limb use statistics. Accordingly, we predicted that SMC in individuals suffering from lower limb loss would not undergo substantial reorganization under the assumption that lower limb functions such as standing, balancing and ambulation are largely invariant to limb loss, particularly with the use of standard prosthetics.…”

Neural encoding of actual and imagined touch within human posterior parietal cortex

“…Similar stability in the topography of the somatosensory cortex has been identified in human subjects that have suffered limb amputations. In these amputees, there is a preserved digit map within the primary somatosensory cortex ( Kikkert et al, 2016 ; Makin and Flor, 2020 ).…”