## 4 Discussion  
The definition of specific intervention groups among a paediatric population is complex and it is of great importance considering that brain damage is an heterogeneous impairment itself. Traditionally, paediatric brain damage englobes both CP and acquired paediatric brain injury [78]. CP is defined as group of permanent disorders of movement and posture caused by a non-progressive brain injury, during the prenatal, natal, or perinatal period [1]. On the other hand, paediatric acquired brain injury includes injuries caused by external or internal factors starting from early childhood [2,3]. There has always been some controversy in whether the term of CP must be included in acquired brain injury, as it is in fact caused by a brain damage, and when to determine the time limit to make the differential diagnosis between the two terms [3]. Giving this lack of consensus, in order to include a wider population, our sample is determined to include children with non-progressive brain damage, whether it is titled as CP or acquired brain injury. Paediatric brain damage causes a wide broad of manifestations, such as cognitive and motor impairments. One of the impairments with the highest impact in daily living functionality is UL function, as it is essential to execute bimanual activities and allow the child's daily living participation and environment exploration, allowing the acquisition and development of cognitive and motor skills [79,80]. Both VR and tDCS have shown benefits in UL function rehabilitation, but there is no evidence of the effects of these two techniques used in a combined protocol. An intervention combining VR and tDCS for UL function in paediatric brain damage is proposed. VR was considered as one of the key elements of the protocol not only for its possibility to include the gamification aspect, so important in children, but also for the accumulated evidence supporting its effects on UL mobility and functional integration in daily living activities. Notably, gaming devices like the Nintendo(r) Wii device (Nintendo, Japan, Kyoto) have been utilised in research, yielding improvements in spasticity, grip strength, and hand function in children with CP, as demonstrated in studies by [PERSON] and [PERSON] [81] and [PERSON] et al. [82], and summarised in [PERSON] et al. 's review [83], which suggests that Nintendo Wii interventions can outperform conventional therapy in functional capacity and dexterity. Devices allowing a better integration of hand movements, such as the Leap Motion controller, have been associated with even more pronounced gains in grip and pinch strength, as stated in [PERSON] et al. 's study [26]. This is the reason why the RGS (Eodyne, Barcelona, Spain) was selected for the protocol, as it is a VR approach that tracks the whole arm motion with a Kinect motion capture system (Microsoft, Redmond, WA, USA), and finger movements with the Leap Motion controller (Ultraleap, San Francisco, CA, USA) to translate them to an artificial environment. The virtual limbs are controlled in a first-person perspective, adding a better embodiment experience. The games used require the use of the trunk, shoulder, elbow, wrist, hand, and fingers, allowing a wide UL training [22]. Our main intention was to develop and test a combined non-invasive neuromodulation protocol. The networks activated by VR rehabilitation are wide and include cognitive attentional areas as well as visuospatial and pre-motor areas; which seems a fairly good combination with the cortical stimulation with tDCS focused in M1 to achieve our objective. This combined approach is initially focused on motor rehabilitation but, according to recent evidence on wide networks, involving motor areas may also enhance cognitive effects. The two most used techniques among the non-invasive neuromodulation are repetitive transcranial magnetic stimulation (rTMS) and tDCS. Both techniques, although based on different principles of action, look for cortical stimulation or inhibition over a certain brain area.