Fuel for Thought? A Systematic Review of Neuroimaging Studies into Glucose Enhancement of Cognitive Performance.

A transient improvement in cognitive performance can be observed following the ingestion of a glucose drink, a phenomenon known as the 'glucose facilitation effect'. The effect has been studied thoroughly in the last three decades, but its neural underpinnings remain a matter of speculation. A systematic review was conducted to evaluate the current evidence from studies applying neuroimaging or neurophysiological methods to investigate the glucose enhancement effect. Eleven studies met the inclusion criteria of using neuroimaging in conjunction with cognitive outcomes. Six studies employed electroencephalography (EEG), four used functional magnetic resonance imaging (fMRI) and one employed functional near-infrared spectroscopy (fNIRS). All but one study reported modulation of neurophysiology or neuroimaging markers following glucose, while only five studies reported significant changes in cognitive outcomes. The evidence suggests that glucose administration enhances neurocognitive markers of episodic memory and attentional processes underpinned by medial temporal and frontal activation, sometimes in the absence of measurable behavioural effects. Further exploration of glucose facilitation using neuroimaging measures with increased sample sizes is warranted to replicate these findings.

Neurochemical changes in the aging brain: A systematic review.

Magnetic resonance spectroscopy (MRS) holds promise for understanding neurochemical mechanisms associated with human cognitive aging in vivo. Recent advances in magnetic field strength and methods provide the opportunity to examine neurometabolites with greater accuracy and detail. The current review summarizes recent literature on age-associated neurometabolite changes as measured by proton MRS, and the associations with cognition in non-clinical populations. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, 179 studies were screened for review, of these, 42 were eligible. When a subset of studies were assessed based on voxel placement, magnetic field strength and sample size, N acetyl aspartate (NAA) concentration was consistently reduced with age predominantly in the frontal lobe and Myo-inositol (mI) concentration increased with age consistently in the posterior cingulate cortex (PCC). These findings are of particular interest as these NAA and mI changes mirror neurometabolite changes often seen in Alzheimer disease. The findings of this review provide further evidence of the potential for 1H-MRS to track age-related neurometabolite changes.