# Resting-State Functional Connectivity in Mathematical Expertise
## 4 Discussion
### Functional Connectivity in Mathematicians  
The intrinsic connectivity of resting-state data has functional significance by encoding and supporting the consolidation of experiences, and thus, it even facilitates behavior performance [60]. This indicates that the connectivity observed from the resting-state data may implicate the possible roles of the involved networks. The mathematicians' group revealed significantly enhanced resting-state connectivity between the frontal and subcortical regions compared to non-mathematicians. Among this constellation of brain areas, we found that the frontal and temporal areas were significantly linked to the caudate nucleus, putamen, and ventral diencephalon that have been known to be closely intertwined with expertise-dependent network [1; 61; 62]. Much evidence has described the role of the caudate nucleus as the formation of a stimulus-response association in the pursuit of moderating goal-directed behavior [63; 64]. The stimulus-response association is one of the features that distinguishes experts from novices. It has been suggested that experts retrieve chunks, patterns, or templates that are made of stimulus-response associations stored in the long-term memory and apply them for their professional performance [65; 66; 67]. Therefore, the involvement of the caudate nucleus in our mathematician group may be pertinent to its supporting role of expert-specific operation with arithmetical knowledge structures stored in the long-term memory. The occipital gyrus that was connected to the caudate nucleus in the mathematician group is also construed as aiding expertise-related behaviors. Professional mathematicians are likely to retrieve arithmetical facts from stimulus-response associations instead of getting involved in actual calculation, and as a result, mathematicians compile mathematical chunks in the occipito-temporal visual cortex [68]. In line with this, the present study also showed the significant connection between the caudate nucleus and the right inferior occipital gyrus only in mathematicians. The frontostrriatal network, including the caudate nucleus, putamen, and thalamus (vental diencephalon), in mathematicians was another major finding in the present study. The caudate nucleus and putamen, together with the ventral precentral gyrus, were the key connections modulated by mathematical competence according to the functional connectivity measured by psychophysiological interactions (PPIs) [1]. In terms of the thalamus, the spontaneous thalamic activity obtained by resting-state functional connectivity supports the key role of the fronto-thalamic connections in expertise, showing that the connections between the thalamus and inferior/middle frontal gyrus were positively correlated with experts' training time [69]. The thalamus, in association with the prefrontal cortex and caudate nucleus/putamen, have been adduced not only as a hub for integrating information across cortical networks [70], but also as a mediation of many cognitive functions, such as spatial visual processing, attention, memory, and decision making [71; 72; 73; 74]. Therefore, the involvement of the thalamus in the form of fronto-thalamic connections among mathematicians may be indicative of its active involvement in mathematics, which resultingly expedites information processing within the network and facilitates mathematicians' professional performance in mathematics. Another noteworthy connection in mathematicians was observed in the medial temporal lobe linked to the basal ganglia and inferior frontal gyrus (pars orbitals). The inferior temporal regions and inferior frontal gyrus were found to be sensitively activated to quantity- and mathematics-related concepts [75]. When professional mathematicians were involved in the processing of mathematical statements (e.g., algebra, analysis, topology, or geometry), they showed activation in the inferior temporal region, along with the bilateral intraparietal sulci and bilateral sites in the dorsolateral, superior, and mesial prefrontal cortex [76].