Glucose effects on cognition in schizophrenia

Abstract

Clozapine has been shown to improve verbal declarative memory and other cognitive functions in chronic schizophrenia. This raises the possibility that additional adjunctive manipulations might improve memory further. In this study, we hypothesized that glucose, which improves memory in a variety of conditions, including schizophrenia, would improve memory more than saccharin in a group of patients stabilized on clozapine. Twelve outpatients with schizophrenia who received treatment with clozapine participated in a double-blind, counterbalanced, crossover study. Subjects received beverages containing either glucose or saccharin on one occasion, and then the other beverage about a week later. Fifteen minutes after ingesting the beverage, subjects received a brief battery of neuropsychological tests to assess verbal declarative memory, attention, and executive functions. Blood glucose levels were assessed at baseline, and at 15 and 50 min after beverage ingestion. The main findings were that retention of a list of words was improved in the glucose condition, while performance on a complex test of sustained vigilance declined after glucose ingestion. These findings provide evidence that glucose improves declarative memory in patients with schizophrenia who were treated with clozapine, and underscore the possibility of developing effective protocols to reduce cognitive dysfunctions in the disorder. They also highlight the need to explore the extent to which glucose modulates nonmemory cognitive functions such as attention, and to understand more generally how glucose availability and regulation influence cognition.