Effects of overnight fasting on working memory-related brain network: an fMRI study.

Glucose metabolism serves as the central source of energy for the human brain. Little is known about the effects of blood glucose level (BGL) on higher-order cognitive functions within a physiological range (e.g., after overnight fasting). In this randomized, placebo-controlled, double blind study, we assessed the impact of overnight fasting (14 h) on brain activation during a working memory task. We sought to mimic BGLs that occur naturally in healthy humans after overnight fasting. After standardized periods of food restriction, 40 (20 male) healthy participants were randomly assigned to receive either glucagon to balance the BGL or placebo (NaCl). A parametric fMRI paradigm, including 2-back and 0-back tasks, was used. Subclinically low BGL following overnight fasting was found to be linked to reduced involvement of the bilateral dorsal midline thalamus and the bilateral basal ganglia, suggesting high sensitivity of those regions to minimal changes in BGLs. Our results indicate that overnight fasting leads to physiologically low levels of glucose, impacting brain activation during working memory tasks even when there are no differences in cognitive performance.

Generalized deficit in all core components of empathy in schizophrenia.

Empathy is a multidimensional construct composed of several components such as emotion recognition, emotional perspective taking and affective responsiveness. Patients with schizophrenia demonstrate deficits in several domains of emotion processing and perspective taking, thus suggesting a dysfunctional emotional competence. We assessed empathic abilities via three paradigms measuring emotion recognition, perspective taking and affective responsiveness as well as self-report empathy questionnaires in 24 (12 females, 12 males) schizophrenia patients meeting the DSM-IV criteria for schizophrenia and 24 matched healthy volunteers. Patients were recruited from the Department of Psychiatry and Psychotherapy, RWTH Aachen University and healthy volunteers were recruited via advertisement. Groups were matched for age, gender and parental education. Data analysis indicates a significant empathic deficit in patients, reflected in worse performance in all three domains. This deficit was only partly reflected in the self-report empathy questionnaires. Comparing the different tasks, emotional perspective taking was the most difficult task for all subjects and symptomatology worsened affective responsiveness. Schizophrenia patients not only struggle to correctly identify emotions, but also have difficulties in spontaneously simulating another person's subjective world (perspective taking) and might not be able to respond adequately in terms of their own emotional experience (affective responsiveness), which are not caused by emotion perception deficits. The results suggest that all domains of empathy are affected in schizophrenia and have to be addressed independently in behavioral therapies, thereby offering a possibility to improve socio-occupational life.

Investigating the impact of overnight fasting on intrinsic functional connectivity: a double-blind fMRI study.

The human brain depends mainly on glucose supply from circulating blood as an energy substrate for its metabolism. Most of the energy produced by glucose catabolism in the brain is used to support intrinsic communication purposes in the absence of goal-directed activity. This intrinsic brain function can be detected with fMRI as synchronized fluctuations of the BOLD signal forming functional networks. Here, we report results from a double-blind, placebo controlled, cross-over study addressing changes in intrinsic brain activity in the context of very low, yet physiological, blood glucose levels after overnight fasting. Comparison of four major resting state networks in a fasting state and a state of elevated blood glucose levels after glucagon infusion revealed altered patterns of functional connectivity only in a small region of the posterior default mode network, while the rest of the networks appeared unaffected. Furthermore, low blood glucose was associated with changes in the right frontoparietal network after cognitive effort. Our results suggest that fasting has only limited impact on intrinsic brain activity, while a detrimental impact on a network related to attention is only observable following cognitive effort, which is in line with ego depletion and its reliance on glucose.