83 ALTERED VISUOMOTOR PROCESSING IN NA 4 functionally connected to regions that are not part of the default mode network, such as somatosensory and somatomotor areas. 172 These connections fit with the region’s taskfocused functions. The decreased activity along the parieto-occipital sulcus thus likely reflects altered processing and integration of self-relevant visuomotor information in NA patients. Behavioural task effects While the cerebral alterations in NA patients were specific to the affected upper extremity, patients were slower than healthy participants with both their affected and unaffected extremity. This deviates from our previous behavioural study, where we found decreased accuracy specific to the affected limb in an independent sample of NA patients. 122 Interestingly, both unilateral and bilateral deficits in both RT and accuracy have been reported in other asymmetric upper extremity disorders. 31, 71, 72, 98, 117, 163, 173 These differing results may stem from differences in patient populations and experimental settings. NA patients in the current study were tested at an earlier disease stage (median/mean of 8/17 months after onset) than our previous sample (16/61 months). 122 Furthermore, here patients performed the task in a supine position while lying in the MRI-scanner, whereas the patients in our previous behavioural study were sitting up-right in a more natural environment. 122 The effect of the MRI-scanner environment on performance may have differed between patients and healthy participants, which could explain why patients were slower, but did not show decreased accuracy compared to healthy participants. Likewise, the overall slowing of responses could be a generic consequence of residual NA symptoms like fatigue, 6, 8, 10 which may have been exacerbated by the demanding MRIscanner environment. 174 Alternatively, the bilateral behavioural impairment may reflect an increased reliance on sensorimotor representations of the unaffected extremity, subsequently slowing responses for both extremities. 173 Importantly, the cerebral alterations were specific to the affected limb, which might reflect the ability of fMRI to capture differences in cerebral processes between conditions, even when behavioural performance (e.g. reaction time) stays constant. 175-178 Our finding that increased activity along the parieto-occipital sulcus correlated with faster reaction times (for the affected limb) suggests that this region is relevant for task performance. 175, 178 Furthermore, the negative correlation between task-related activity in the extrastriate cortex and residual NA symptoms (persistent pain related to motor dysfunction) suggests that this brain region is also relevant for NA. Follow-up longitudinal studies might be able to characterize the relative dynamics of cerebral and behavioural alterations in NA. Interpretational issues There has been some debate on the exact processes underlying hand laterality. It has been mainly assumed that this task involves implicit motor imagery; whereby participants imagine moving their hand to match the stimulus hand. 24, 25, 71, 76, 86 Recently, it has been proposed that this task does not involve motor imagery, but rather relies on visual strategies84, 85 and multisensory integration, whereby multisensory binding of the proprioceptive representation of the own hand and the visual representation of the hand stimulus are used to determine hand laterality. 87 Both motor imagery and multisensory integration involve sensorimotor representations of the upper extremity, which means that hand laterality judgment can be utilized to study these representations
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