## 4 Discussion
### White Matter Integrity  
Studies have reported that FA characterizes directionality of constrained water diffusion in the brain tissue [37]. In addition, changes in FA are affected by many factors, including neuron numbers, density, diameter, and myelin sheath thickness [79]. In this study, an increase in FA was observed in the GOCC and R.ACR of the exercise group, although it decreased in the control category. These results should be further evaluated.  
Figure 2: FA mediated the association between motor learning and working memory. Depiction of the applied mediation model: Unstandardized coefficients and standard errors for each path of the mediation model are presented. Note that c represents the direct effect while c\({}^{\prime}\) denotes the indirect effect. * indicates significance at \(p<0.05\).  
There was a significant increase in the FA of GOCC and right ACR in the experimental group. An increase in FA is generally considered to indicate an improvement in WMI. In addition, the corpus callosum (CC) has been shown to have an important role in interhemispheric communication and synchrony [80] as it is the bundle of white matter that connects the left and right cerebral hemispheres. The anterior part of CC contains fibers projecting into the prefrontal, premotor, and supplementary motor cortical areas [81]. Therefore, it could be involved in any aspect of cognitive function, especially those involving higher cognitive abilities. Moreover, radiating corona projects upward to the motor area as well as the anterior motor area of the cerebral cortex and reaches down to the posterior limb of the internal capsule and the cerebrum. This is the place where motor and sensory conduction fibers are highly concentrated [33]. These findings were confirmed by previous studies on badminton [33], visual space training [82], and finger sequence learning [34]. Therefore, we hypothesized that football juggling improves WMI in these areas, thereby enhancing cortical associations linked to movement.  
Interestingly, we also revealed structural changes in the brains of participants in the control group. Low FA values were recorded in the GOCC and right ACR in the control group, and this phenomenon may be consistent with lifelong brain development. Studies have shown that most of the peak values in FA and MD occur before the age of 35. Macrostructurally, the total volume of the brain is usually at 90% complete development by the age 6 [83, 84]. Early development of the CC has been confirmed, with most of the changes occurring before adolescence or the age of 20 [85]. Therefore, it was postulated that changes observed in the GOCC and Right ACR of the control group, were normal phenomena in lifelong brain development.  
Additionally, recent studies have evaluated the effects of motor learning on the brain, and evidence shows that motor learning can cause microstructural changes in WMI [28, 30, 32]. The theory of brain plasticity has been supported by studies highlighting that brain structure and function can continuously be shaped by the external environment and experience. Our findings also confirm that motor learning causes changes in WMI.