Age-related differences in GABA levels are driven by bulk tissue changes

Levels of GABA, the main inhibitory neurotransmitter in the brain, can be regionally quantified usingmagnetic resonance spectroscopy (MRS). Although GABA is crucial for efficient neuronalfunctioning, little is known about age-related differences in GABA levels and their relationship to age-relatedchanges in brain structure. Here, we investigated the effect of age on GABA levels within theleft sensorimotor cortex as well as the occipital cortex in a sample of 85 young and 85 older adultsusing the MEGA-PRESS sequence. Because the distribution of GABA varies across different braintissues, various correction methods are available to account for this variation. Considering that thesecorrection methods are highly dependent on the tissue composition of the voxel of interest, weexamined differences in voxel composition between age groups as well as the impact of these variouscorrection methods on the identification of age-related differences in GABA levels. Results indicatedthat, within both voxels of interest, older (as compared to young adults) exhibited smaller gray matterfraction accompanied by larger fraction of cerebrospinal fluid. Whereas uncorrected GABA levelswere significantly lower in older as compared to young adults, this age effect was absent when GABAlevels were corrected for voxel composition. These results suggest that age-related differences inGABA levels are at least partly driven by the age-related gray matter loss. However, as alterations inGABA levels might be region-specific, further research should clarify to what extent gray matterchanges may account for age-related differences in GABA levels within other brain regions.

Publication year:2018