# A Meta-Analysis on Dual Protocols for Chronic Stroke Motor Recovery: Robotic Training and tDCS
## 4 Discussion
The future studies need to confirm whether tDCS protocols in addition to robotic training improve kinematic and kinetic variables on paretic arms. To advance motor recovery of the upper limbs post-stroke, administering bilateral robot-assisted rehabilitation programs coupled with bilateral tDCS protocols may be beneficial. Previous stroke rehabilitation studies have raised the possibility that functional improvements in the paretic arms may be better facilitated after bilateral treatments with robot devices such as an end-effector and exoskeleton systems as compared with unilateral robotic training protocols [80; 81; 82]. Potentially, bimanual movements may increase inter-limb coupling, contributing to motor recovery of the paretic arms. This would be due to rebalanced inter-hemispheric inhibitions between hemispheres and greater involvement of both the contralateral pathway from the ipsilesional hemisphere as well as the ipsilateral pathway from the contralesional hemisphere to the affected upper limb [6; 81; 83]. Similarly, bilateral tDCS protocols such as anodal tDCS on the primary motor area (M1) of the ipsilesional hemisphere, and cathodal tDCS on the M1 of contralesional hemisphere, may enhance paretic arm functions via modulating and balancing cortical excitation and inhibition between hemispheres [84]. Nevertheless, nearly all of the included studies in this meta-analysis used unimanual robotic training protocols with active tDCS to stimulate the affected unilateral hemisphere. Taken together, these findings demonstrate that robotic training combined with tDCS protocols for advancing upper limb rehabilitation may target both sides of the central and peripheral nervous system. For the five lower limb rehabilitation studies, robotic training combined with tDCS protocols revealed greater positive effects on gait functions post-stroke than those observed for robotic training only. These additional treatment effects were observed in the post-test conducted directly after the final intervention from the five comparisons, as well as in follow-uptests from the four comparisons. These meta-analytic findings support the proposition that non-invasive brain stimulation techniques administered with task-specific physical interventions may facilitate progress toward motor recovery in patients with stroke [14]. Recent meta-analysis studies indicated a possibility that applying specific tDCS montages (e.g., bihemispheric stimulation) can improve mobility, lower limb muscle strength, and gait functions estimated by clinical measurements in patients with stroke [85; 86]. Presumably, stimulating motor cortical regions in both the affected and unaffected hemispheres may influence and trigger corticospinal and brainstem-spinal descending pathways, contributing to modulating the spinal central pattern generators [87; 88; 89]. Moreover, robot-assisted gait training can allow both ambulatory and non-ambulatory patients with stroke to perform intensive, repetitive, and complex walking practices, with more body weight support for patients and convenient administration for clinicians [90]. Thus, combining the top-down and bottom-up rehabilitation approaches may effectively increase neural plasticity and functional recovery across the central and peripheral nervous systems post-stroke. However, given that the number of included studies seems to be rather sparse, more studies will be necessary for validating potential treatment effects of tDCS protocols combined with robotic training on functional recovery of the lower limbs post-stroke. Despite the potential additive effects of tDCS protocols with robotic training on post-stroke motor recovery, these findings should be cautiously interpreted. First, given that the qualified studies in this meta-analysis included no acute stroke patients, the current meta-analytic findings might be limited to subacute or chronic stroke patients.