## 4 Discussion  
In the present work, we asked the question of whether patients with SCI show differential effects in connectivity patterns in response to movement and imagination of movement depending on whether they are sportive or not. We investigated the effect of sports on cortical connectivity in patients with SCI and healthy participants during movement imagination and movement execution using HD-EEG. We found different patterns in connectivity between the non-sorptive groups and sport groups, suggesting a modulative effect of sports on cortical connectivity. We can answer our research question because we found indication for a modulative effect of sportive activity, both in healthy controls and patients, but to a different extent. This was indicated by a different pattern of activation of movement- and imagination-relevant brain networks in healthy controls and patients depending on whether they practiced sports regularly or not. Exercise plays an important role in rehabilitation of patients with SCI. However, not many EEG studies have been conducted to investigate the influence of sports on the cortical activity in SCI patients. Searching Pubmed in January 2023 with the terms \"spinal cord injury + EEG + sports\", \"spinal cord injury + EEG + exercise\", and \"spinal cord injury + EEG + physical activity\" yielded a clear gap in knowledge in this area. Thirty-three out of the 38 retrieved studies did not concern sports, but gait training, physiotherapy, or brain-computer interface training. The five studies left tested the acute effect of training conducted during the experiment (see Supplementary Table S3) [41; 42; 43; 44; 45]. Hence, the influence of regular exercise on long-lasting changes in cortical connectivity had not been addressed thus far. Prior research demonstrated that patients with SCI exhibit an increased cortical excitability [46; 47; 48] that might enhance neuroplastic changes in the cortex. Neuroplasticity is known to be driven by the brain derived neurotrophic factor (BDNF), which, according to  
Figure 6: Directed connectivity during the condition imagination, the sound music, and the frequency beta from (**a**) M11 to S1r, (**b**) S11 to M1r, (**c**) PMC1 to S1r, (**d**) S11 to S1r, and (**e**) PMC1 to M11. SCI = spinal cord injury, RTE = relative treatment effect, MI = left primary motor cortex, S1r/l = right/left primary somatosensory cortex, PMC1 = left premotor cortex. a study by [PERSON] and colleagues, is released during exercise and reaches a level six times higher in athletes with SCI at rest compared to healthy participants [49]. The authors also reported that the BDNF level further increased during light hand-bike training and suggested that exercise boosts neuroplastic changes in patients with SCI. The data of our study support this hypothesis, as the difference in sport groups, i.e., the instance that one group is sportive while the other is not, causes a higher difference in connectivity in patients with SCI compared to the healthy participants in the observed brain areas for the alpha frequency range during the imagination condition. It seems plausible that neuroplasticity is facilitated due to the increased cortical excitability and elevated BDNF levels. We speculate that this is the reason why cortical connectivity is more prone to changes due to regular exercise in patients with SCI compared to healthy participants. Interestingly, this difference can be observed mainly during movement imagination, not during the actual movement where the pattern of results looked quite different. It is possible that the results in the movement condition are biased by the rhythmic movement artefacts, such that interpretation should be performed only cautiously, if at all. Furthermore, none of the effects in the movement condition were significant after correction for multiple comparisons. Even though movement and movement imagination showed similar patterns in brain activation in prior research [50; 51], there were still important differences.