What makes a network complex, in addition to its size, is the interconnected interactions between elements, disruption of which inevitably results in dysfunction. Likewise, the brain networks complexity arises from interactions beyond pair connections, as it is simplistic to assume that in complex networks state of a link is independently determined only according to its two constituting nodes. This is particularly of note in genetically complex brain impairments, such as the autism spectrum disorder (ASD). Accordingly, structural balance theory (SBT) affirms that in the real-world signed networks, a link is remarkably influenced by each of its two nodes interactions with the third node within a triadic interrelationship. Thus, it is plausible to ask whether ASD is associated with altered structural balance resulting from atypical triadic interactions. In other words, it is the abnormal interplay of positive and negative interactions that matter in ASD, besides and beyond hypo (hyper) pair connectivity. To address this, we explore triadic interactions in the rs-fMRI network of participants with ASD relative to healthy controls (CON). We demonstrate that balanced triads are overrepresented in the ASD and CON networks while unbalanced triads are underrepresented, providing first-time empirical evidence for the strong notion of structural balance on the brain networks. We further analyze the frequency and energy distribution of triads and suggest an alternative description for the reduced functional integration and segregation in the ASD brain networks. Last but not least, we observe that energy of the salient and the default mode networks are lower in autism, which may be a reflection of the difficulty in flexible behaviors. Altogether, these results highlight the potential value of SBT as a new perspective in functional connectivity studies, especially in neurodevelopmental disorders.
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