Age-Related Declines in Occipital GABA are Associated with Reduced Fluid Processing Ability

Rationale and objectives: Healthy aging is associated with pervasive declines in cognitive, motor, and sensory functioning. There are, however, substantial individual differences in behavioral performance among older adults. Several lines of animal research link age-related reductions of gamma-aminobutyric acid (GABA), the brain's primary inhibitory neurotransmitter, to age-related cognitive, motor, and sensory decline. Our study used proton magnetic resonance spectroscopy (MRS) at 3T to explore whether occipital GABA declines with age in humans and whether individual differences in occipital GABA are linked to individual differences in fluid processing ability.

Materials and methods: We used a MEGA-PRESS sequence that combines frequency spectral editing with a point-resolved spectroscopy sequence to quantify GABA. Spectra were obtained from a 30 × 30 × 25 mm voxel placed in the occipital cortex of 20 young adults (mean age 20.7 years) and 18 older adults (mean age 76.5 years). Participants also performed 11 fluid processing tasks outside the scanner, the results of which were z-scored and averaged to calculate a summary measure of fluid processing ability. Regression analysis was employed to determine the relationship between GABA concentrations in the occipital cortex and a summary measure of fluid processing ability.

Results: Occipital GABA was significantly lower in older participants compared to the younger participants. We also observed a significant positive relationship between occipital GABA and fluid processing ability. In fact, higher GABA was associated with better task performance in 10 of the 11 tasks.

Conclusion: These findings suggest that GABA levels decline with age in humans and are associated with declines in fluid processing ability.