Adjacent networks share a spatial motif, potentially reflecting common origins.
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Networks are differentially specialized for language, social and mnemonic/spatial functions.
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We propose the expansion-fractionation-specialization (EFS) hypothesis.
Humans can reason about other minds, comprehend language and imagine. These abilities depend on association regions that exhibit evolutionary expansion and prolonged postnatal development. Precision maps within individuals reveal these expanded zones are populated by multiple specialized networks that each possess a spatially distributed motif but remain anatomically separated throughout the cortex for language, social, and mnemonic/spatial functions. Rather than converge on multi-domain regions or hubs, these networks include distinct regions within rostral prefrontal, temporal, and midline association zones. To account for these observations, we propose the expansion-fractionation-specialization (EFS) hypothesis: evolutionary expansion of human association cortex may have allowed for an archetype distributed network to fractionate into multiple specialized networks. Human development may recapitulate fractionation and specialization when these abilities emerge.