## 4 Discussion
### Informative Biomarkers  
The proposed framework incorporated multiple biological and non-biological attributes in order to identify discriminative biomarkers containing autism-related information in a global manner. As such, the selected 136 features included 43 interconnected pairs of sFC, 47 mean dFC, 45 variance FC, and one acquisition parameter. This fact suggests the effectiveness of FC in the context of ASD detection, while at the same time provides indications of the small relevance of non-physiological measurements with regard to ASD classification. However, the addition of the protocol's attributes of each fMRI magnet acquisition process in the form of the TE feature denotes the use of mixed datasets (with data from various clinics) as an interesting possibility to decipher the global autism substrates regardless of acquisition parameter deviations. From this standpoint, it can be inferred that the employment of the fMRI setup specifications, when mapped to higher dimensions, can augment classification performance with heterogeneous data deriving from different sites, while increasing the sample size and, therefore, generalization. In regard to the physiological features, FC was estimated for the DMN regions from the CC200 brain parcellation scheme. Although whole-brain analysis would provide an expanded number of FC to incorporate in the FS and classification framework offering additional ASD information, evidence suggests that autism-related regulations are more prominent in the DMN. For instance, in [32], the DMN FC patterns are identified as differentiated in ASD individuals; nevertheless, when whole-brain analysis was conducted, no significant changes could be discerned. This fact along with the higher computational cost of calculating the FC for a plethora of brain regions further promotes the DMN utilization over whole-brain analysis. Pertaining to the selected FC features, dFC was involved in almost 2/3 (90 out of 136) of all the incorporated feature vectors, denoting distinct states as a relation of time variable brain activation. In fact, several studies also demonstrate the efficiency of dynamic connectivity in comparison to stationary brain dynamics, suggesting that dynamic analysis can provide evidence about smaller nodes activation (concealed in the stationary analysis) and revealing hidden information of the way the various illnesses can regulate brain-related mechanisms [33; 48]. Concerning specific connectivity notes, our results indicate several DMN areas as potential biomarkers for autism detection. In detail, the frontal medial cortex has been associated to the individuals' emotional state [49; 50], while the paracingulate is linked to reality monitoring and emotion processing [51; 52]. Since ASD individuals typically demonstrate socio-emotional difficulties and/or social withdrawal [53], FC implicating the aforementioned brain regions is expected. In a similar manner, ASD display atypical relational memory processes [54], corroborating our findings with regard to FC edges implicating the parahippocampal gyrus (related to relational encoding [55; 56]) and the precuneus (involved in environmental perception, cue reactivity, and episodic memory retrieval [57]). Moreover, our results indicate the occipital areas as important biomarkers for autism detection. This is supported by other relevant studies, linking occipital regions with categorization/organization of various information, as well as with face recognition [58; 59], of which deficits are consistently reported in ASD [60]. Further analysis was performed by employing a Wilcoxon test in the selected features. In this light, most features did not display statistically significant differences between the ASD and TD groups, which can be attributed to subject variability, acquisition protocol, etc. From the overall of 136 features, 19 demonstrated significant divergence between the two groups. Remarkably, all features consisted of sFC and mean dFC with a clear overall trend of an increasing Pearson correlation coefficient from TD to ASD.