In this study, we suggest plasticity changes of functional connectivity induced by long-term motor training are correlated with semantic processing in an effector-specific manner. Firstly, building upon and expanding the findings of previous studies (Hervais-Adelman et al., 2015; Amad et al., 2017), our results indicate that long-term expertise in football training enhances the functional connectivity between the general semantic system and the motor-related cortex. Secondly, we observed that the plasticity changes in brain functional connectivity correlated with the behavioral performance in semantic tasks. Our findings thus provide further supporting evidence for the notion that semantic processing is rooted in the sensory-motor system.
The results presented in this study bolster the hypothesis that the neural systems instrumental in forming and retrieving semantic knowledge overlap with those essential for perceiving various sensory modalities or executing actions. Our findings suggest that long-term motor training increases the functional connectivity between semantic processing regions and motor processing regions. Specifically, we observed an increased correlation between the foot execution region and the right MTG in expert football athletes compared to novices. The right MTG has been associated with semantic processing (Jung et al., 2017). Furthermore, experts showed an increase in functional connectivity between the left aMTG and the ACC, Supplementary Motor Area (SMA), bilateral Paracentral Lobule (PL), and right medial Superior Frontal Gyrus (SFG). These areas (ACC, SMA, PL, and medial SFG) are intricately involved in motor control and coordination, particularly for complex, voluntary movements and movements involving the lower extremities (Paus, 2001; Wenderoth et al., 2005; Tanji, 2001; La Fougère et al., 2010; Rizzolatti & Luppino, 2001).On the other hand, the left aMTG plays a crucial role in many domains of language processing (Xu et al., 2019; Visser et al., 2012), and its connectivity with primary and secondary sensory-motor areas has been associated with semantic processing (Riccardi et al., 2019). Moreover, the analysis revealed that experts also showed increased functional connectivity between the left aITG and the Mid-Cingulate Cortex (MCC) and PL. From the aTFC seed, experts demonstrated increased functional connectivity with the left Superior Parietal Lobule (SPL), left Inferior Parietal Lobule (IPL), and left Postcentral Gyrus (PoG). The IPL has been associated with the mirror neuron system, thought to be involved in understanding and imitating the actions of others (Rizzolatti & Sinigaglia, 2010). A recent study suggests that the IPL plays a critical role when visuo-motor coordination is required for action (Johari et al., 2022). As shown in Table 1 and Fig. 2, novices showed increased connectivity between TP and right MTG and between aPHG and right MTG. Both of these FCs are within the general semantic system, suggesting that novices may have superior general semantic processing capabilities than football athletes. The advantages of football athletes are reflected in semantic processing of concrete action verbs, especially those related to foot actions. Taken together, our results indicate that long-term foot-related motor training may correlate to plasticity changes in brain functional connectivity between semantic processing and motor processing areas, further enhancing our understanding of the connection between physical training and cognitive functions.
Interestingly, our results also showed that the FCs that showed differences between groups could significantly predict the drift rate of foot verbs in both experts and novices, but not the drift rate of hand verbs. This consistency across groups indicates that FCs exhibiting plastic changes is indeed linked to the semantic processing of foot action verbs. Within our predictive models, we found that FCs between aMTG and MFG/SMA, and between aPHG and right MTG, were significant predictors for the drift rate of foot verbs in experts. However, for the drift rate of hand verbs in experts, only the connectivity between aPHG and right MTG emerged as a significant predictor. These results imply that the FC between aMTG and MFG/SMA might be influenced by motor experience, impacting the semantic understanding of foot action verbs. In contrast, the connectivity between aPHG and right MTG, which remains a constant predictor across verb categories, suggests its pivotal role in the broader comprehension of action language, independent of motor experience. SMA plays a crucial role for linking cognition to action (Nachev et al., 2008). SMA is crucial for motor execution and motor plan (Hardwick et al., 2018), moreover, it is also considered to play a significant role in language processing (Hertrich et al., 2016). The current study discovered that the connectivity between the SMA and MTG brain regions may be modulated by motor experience, and that this connectivity is associated with the semantic processing process, thereby corroborating the findings of previous research. Further rsFC analysis using SMA as seed showed the SMA was correlated with the bilateral precentral gyrus in experts, whereas in novices, the MFG showed correlation with the right paracentral gyrus and right precentral gyrus. The results further support the vies that the SMA is a key node linking language and action. In sum, these findings align with previous studies suggesting that semantic processing of concrete action verbs is based, at least in part, on motor experience (Fernandino et al., 2022). They further emphasize the crucial roles of FC between aMTG and MFG/SMA and FC between aPHG and MTG in embodied semantic processing (Hauk et al., 2004; Courson et al., 2017; Zhang et al., 2020; Fu et al., 2023).
Notably, we did not find a difference in the drift rate between groups or conditions, likely due to the task's difficulty. However, we found significant differences in response time and non-decision time between groups. Non-decision time, which encompasses the period for encoding and response generation processes (Ratcliff et al., 2016), presents a dual explanation for these findings: either experts possess a superior motor processing ability, or they have an advantage in encoding efficiency. The analysis from our predictive models focusing on non-decision time indicated that FC variations between groups failed to significantly predict the drift rate for foot action verbs among both experts and novices. This suggests that the observed advantages among experts may not stem from motor processing capabilities.