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

Objective: Studies in healthy individuals show that exerting self-control consumes cognitive resources, which reduces subsequent self-control performance. Restoring the availability of blood glucose eliminates this impairment. 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.

Method: 40 patients with schizophrenia-spectrum disorders and 40 normal controls were recruited. A two drinks (glucose vs. placebo)×two depleting phases (self-control depleted vs. non-depleted) between-groups design was used. We examined the blood glucose levels before and after the selfcontrol depletion phase and the subsequent performances in two self-control tasks (handgrip and Stroop tests) after the drink condition.

Results: The four groups (depleting×glucose, depleting×placebo, non-depleting×glucose and nondepleting×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×two between-subjects ANOVAs were carried out to test the performances in the handgrip and Stroop tasks. 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 abnormal glucose facilitation effect in patients during a cognitive self-control task but not during a physical self-control task. The findings also suggested for the first time that a self-control depletion effect is intact in patients with schizophrenia.