Functional brain networks in treatment-resistant schizophrenia

Introduction
Up to 20% of individuals with schizophrenia show minimal or no response to medication and are considered to have ‘treatment-resistant’ schizophrenia (TRS). Unlike early and established schizophrenia, few studies have investigated resting-state functional connectivity (rs-FC) in TRS. Here, we test for disruptions in FC and altered efficiency of functional brain networks in a well-characterized cohort of TRS patients.

Methods
Resting-state functional magnetic resonance imaging was used to investigate functional brain networks in 42 TRS participants prescribed clozapine (30 males, mean age = 41.3(10)) and 42 healthy controls (24 males, mean age = 38.4(10)). Graph analysis was used to characterize between-group differences in local and global efficiency of functional brain network organization as well as the strength of FC.

Results
Global brain FC was reduced in TRS patients (p = 0.0001). Relative to controls, 3.4% of all functional connections showed reduced strength in TRS (p < 0.001), predominantly involving fronto-temporal, fronto-occipital and temporo-occipital connections. Global efficiency was reduced in TRS (p = 0.0015), whereas local efficiency was increased (p = 0.0042).

Conclusions
TRS is associated with widespread reductions in rs-FC and altered network topology. Increased local functional network efficiency coupled with decreased global efficiency suggests that hub-to-hub connections are preferentially affected in TRS. These findings further our understanding of the neurobiological impairments in TRS.