59 ALTERED SENSORIMOTOR REPRESENTATIONS IN NA 3 its introduction, it has been widely assumed that a hand’s laterality is determined by implicitly imagining moving the own hand to match the hand on the screen (i.e. implicit “motor imagery”). 25, 29, 86 Recently, it has been proposed that instead of through motor imagery, laterality is determined through the multisensory binding of the proprioceptive representation of the own hand and the visual representation of the hand on the screen (i.e. multisensory integration). 87 Both motor imagery and multisensory integration involve sensorimotor representations and central sensorimotor processes. Previous neuroimaging studies21, 24 show that the hand laterality judgment task evokes brain activity in regions that are involved in preparation, planning, selection, and execution of movement. 88-91 Furthermore, in previous work the posture congruency effect was specifically associated with brain activity in the posterior parietal cortex, 24, 58 a region that is essential for body schema encoding. 92 Body schema is the integrated neural representation of the body based on somatosensory feedback. 93, 94 In the current study, the posture congruency effect was similar between NA patients and controls, indicating that patients are able to incorporate postural information of their affected upper limb during imagery. We thus propose that the patients’ impaired performance for laterality judgment of their right upper limb is associated with deficits in central sensorimotor processes. Whether this deficit stems from deficient motor, sensory, or integrational processes, remains to be investigated. In line with this idea, we also found that whereas healthy controls were significantly more accurate with their dominant than with their non-dominant limb, patients showed a trend towards the opposite (i.e. lower accuracy for the dominant, affected, limb than for the non-dominant, unaffected, limb). Patients often report reduced use of their affected, dominant limb, and increased use of their unaffected, non-dominant limb. Hence, it could be argued that patients may develop a bias towards the non-affected, non-dominant, limb, and that our results may therefore reflect a shift in limb preference rather than an impairment of the affected limb. However, it has been shown in healthy individuals that while hand-immobilization negatively affects recognition of the immobilized hand in this task, it does not improve performance for the over-used non-immobilized hand.95-97 The effect of long-term limb disuse on task performance has been studied in a small sample of individuals with traumatic brachial plexus injury. Although patients performed worst with their injured, disused limb, performance was also decreased for their uninjured, over-used limb compared to healthy controls. 98 If a bias towards the over-used hand would underly the decrease in performance for the disused hand, a concurrent increase in performance for the over-used hand would be expected. At this time, we cannot determine whether a direct impairment of the affected limb or a bias towards the unaffected limb underlies the altered central sensorimotor representations we found in NA patients in the current study. Changes in central sensorimotor processes after peripheral nerve damage Our findings, and those of others, indicate that patients with peripheral nerve damage are susceptible to changes in the central sensorimotor system, which in turn may influence their clinical symptoms. A growing body of evidence describes how the central nervous system adapts to peripheral nerve injury, and that the adaptations are not always beneficial. Examples include long-lasting reorganization of somatosensory representations
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