Intact functional brain networks in the isolated hemisphere of people after hemispherotomy

Cognition and behaviour are thought to be underpinned by seven segregated brain networks, whose tasks range from the sensory role of the visual network to intrinsic mental processes such as consciousness carried out by the default-mode network. However, it is unclear whether functional integrity of these networks is retained when the brain is devoid of external inputs. Here we investigate the functional organisation of individual brain hemispheres in individuals having undergone hemispherotomy (HT) due to pharmacoresistant epilepsy. Although this procedure results in one hemisphere being isolated from the rest of the nervous system, we find that the functional organisation of the seven macroscale networks is retained in the isolated hemisphere, including the default-mode network. However, both isolated and connected hemispheres have a lower degree of network segregation after HT, compared to healthy brains. Our results indicate that isolated hemispheres preserve functional integrity, thereby instigating inquiries into their cognitive capacities and their potential to be “islands of awareness”.