S110 Phantom limb pain – A correlate of maladaptive neural plasticity

Objectives The majority of limb amputees complain of phantom limb pain (PLP). The primary somatosensory cortex (S1) appears to play a key role in the perception of PLP. However, there is an ongoing debate whether (a) dysfunctional S1 reorganization or (b) preservation of S1 limb representation reflects the more valid correlate of PLP. Methods We tested groups of arm amputees perceiving or not perceiving PLP, implementing tactile stimulation of the lip (testing for reorganization) and executed phantom movements (testing for preserved representation). We further assessed prosthesis use and the users‘ experiences related to the prosthesis. Neural activity in S1 was measured using functional magnetic resonance imaging. Results Amputees with PLP exhibited larger shift of S1 lip representation compared to amputees without PLP. We found no significant S1 activity differences for the execution of phantom movements. Only for lip representation, we found that amputees using a prosthesis showed significantly less dysfunctional reorganization compared to non-users. Perceiving the prosthesis as part of the body was associated with less PLP and dysfunctional reorganization. Discussion Our results support the hypothesis that dysfunctional S1 reorganization reflects a neural correlate of PLP. Prosthesis use in general and prosthesis experiences in particular predict the presence of both dysfunctional reorganization and PLP. Conclusions Maladaptive plasticity processes are associated with PLP. Whether or not dysfunctional S1 reorganization is causally linked to PLP remains open. Significance Our findings contribute to the ongoing scientific debate on the nature of S1 alterations and its importance for the presence or absence of PLP.