Evaluation of long-term cognitive organization after hemispherotomy in Rasmussen's encephalitis: A behavioral and network-level perspective

Hemispherotomy, a neurosurgical procedure that functionally disconnects the affected hemisphere, is the recommended curative treatment for Rasmussen's encephalitis. Following a typically normal developmental period, individuals with Rasmussen's encephalitis develop progressive hemispheric dysfunction and severe epilepsy, ultimately resulting in exclusive “mono-hemispheric” functioning after hemispherotomy. The aim of this study was to provide an in-depth assessment of long-term cognitive outcomes in Rasmussen's encephalitis patients, several years after hemispherotomy. Eighteen patients with Rasmussen's encephalitis (11 on the left hemisphere) underwent extensive cognitive assessment on average more than 14 years after surgery, using a battery of tasks evaluating language, memory, executive functions, and social cognition. The cognitive scores were compared to those of 175 healthy control participants. In addition, graph-based network analyses were conducted on cognitive scores to examine the organization and interactions within the cognitive system. In this extreme mono-hemispheric condition, the entire cognitive network is reorganized. While hemispherotomy maintains a subnormal intellectual efficiency, some functions, such as semantics, memory, and inhibition, tend to be relatively preserved, whereas working memory, syntax, and theory of mind remain impaired in the long term. In the intact hemisphere, strengthened interactions between cognitive functions were observed, especially among patients with a shorter duration of epilepsy before surgery and favorable cognitive recovery. Adopting a network-based perspective on cognition in this clinical context provides novel insights into how cognitive organization and reorganization occur under conditions of profound neuroplasticity.