126 CHAPTER 6 effects. First, we may have lacked power to discern potential group differences in cerebral and behavioral changes because of our small sample size. Alternatively, multidisciplinary rehabilitation may not have elicited greater change in cerebral representations of the upper extremity than usual care. Most patients participated relatively close to their latest NA attack (22/27 patients completed the study within 24 months after onset). Natural recovery processes associated with peripheral nerve recovery6 and training through performing daily activities could have contributed to changes in cerebral sensorimotor representations regardless of the specific rehabilitation program. This may explain why patients in the usual care group also showed increased cerebral activity and improved task performance, despite the fact that more than half of these patients did not report any formal therapy. The fact that multidisciplinary rehabilitation did elicit greater clinical improvement may be understood by taking a closer look at the program. First, occupational therapy is a key component, which often lacks in usual care. It improves clinical outcome by enabling daily activities through training of self-management strategies, 1, 6 but it does not target cerebral motor control. Second, although the specific physical therapy does target cerebral motor control, it was not developed to specifically train the visuomotor processes that we have recently found to be altered in NA. 2 Multidisciplinary rehabilitation may in fact mediate clinical outcome through different cerebral mechanisms, which we did not test with our motor imagery paradigm. Our findings provide valuable insights into (cerebral) recovery in NA, despite the lack of significant cerebral group differences. In our parallel cross-sectional study, we showed that compared to healthy participants, NA patients had decreased brain activity during motor imagery of the affected upper extremity in two visuomotor brain areas: the bilateral parieto-occipital sulcus and the right extrastriate cortex. 2 In the current longitudinal study, we show that patients’ activity in the parieto-occipital sulcus increased in the direction of normality (see Supplementary Figure 2), 2 although we could not directly compare patients to healthy participants at follow-up, as the healthy group was only measured once. The parieto-occipital sulcus is involved in processing and integration of self-relevant information, and hence contributes to a multisensory representation of the spatial location of the own body. 164, 165, 171 Accordingly, increased activity in this region in NA over time may reflect a better encoding of hand position relative to the rest of the body, which is necessary for computing optimal motor plans. Brain activity in the right extrastriate cortex ROI did not change significantly from baseline to followup. However, an unconstrained whole brain analysis, considering both biomechanically complex and easy trials, revealed significant increases in activity related to the affected limb in several ipsilateral occipito-parietal areas. Although located more posteriorly and medially than the ROI in the extrastriate cortex, these areas are part of the same dorsal visual stream. The dorsal visual stream has strong connections with the motor system, and forms an interface between perception and action by integrating visual and proprioceptive information to form sensorimotor representations of the upper extremity. 27, 147, 148 Accordingly, the increased activity in the dorsal visual stream observed in NA patients over time may reflect improved integration of multisensory (visual and proprioceptive) information into motor plans. Combined with our previous findings showing that NA patients have reduced activity compared to healthy controls in the parieto-occipital sulcus and along the dorsal visual stream, 2 the longitudinal findings
RkJQdWJsaXNoZXIy MjY0ODMw