Impaired facilitation of self-control cognition by glucose in patients with schizophrenia : a randomized controlled study

Abstract

Objective: Studies in healthy individuals show that exerting self-control consumes cognitive resources, which reduces subsequent self-control performance. This is termed as the self-control depletion effect. Restoring the availability of blood glucose eliminates this impairment, which is deemed as the glucose facilitation effect. Patients with schizophrenia are found to have self-regulatory dysfunctions. This study aims to investigate whether patient’s (a) glucose facilitation effects will be impaired, and (b) will have exaggerated depletion in a self-control task, as compared with healthy population.

Method: Forty patients with schizophrenia-spectrum disorders and forty normal controls were recruited. This was a two drinks (glucose vs. placebo) x two depleting phases (self-control depleted vs. non-depleted) between-groups design. We examined the blood glucose levels before and after the self-control depletion phase and the subsequent performances in two self-control tasks (handgrip and Stroop Test) after the drink condition.

Results: The four groups (depleting x glucose, depleting x placebo, non-depleting x glucose and non-depleting x placebo) of both patients and normal controls were comparable on a number of characteristics. The change in blood glucose level in the depleting group was significantly different from those in the non-depleting group. Two x two between-subjects ANOVAs were carried out to test the performances in the handgrip and Stroop task. Significant interactions were found in healthy controls regarding both tasks. However, a significant interaction was only found in patients regarding the handgrip task but not the Stroop task.

Conclusions: This study demonstrated an impaired glucose facilitation effect in patients during a cognitive self-control task but not physical self-control task. The findings also suggested for the first time that a self-control depletion effect is intact in patients with schizophrenia, comparing with healthy individuals.