Relationships between GABA+ and Glx concentrations with age and inhibition in healthy older adults

Inhibition represents a core executive function which underlies the ability to suppress interfering and/or distracting stimuli, thereby building resistance against task-irrelevant information. However, the impact of ageing on inhibitory functioning and the potential role of neuroplasticity - largely driven by predominant excitatory (glutamatergic) and inhibitory (GABAergic) neurochemicals - remains poorly understood. In this study, we investigated age relationships with neurochemical concentrations (GABA+ and Glx) and examined the associations between these neurochemicals and inhibitory sub-components in the context of healthy ageing. To this end, participants completed three inhibition tasks (i.e., flanker, Stroop and go/no-go), each measuring a different sub-component process, via the PsyToolkit platform. MRS data was acquired in the sensorimotor (SM1; n=71, mean age (SD) = 68.3 ({+/-}9.7) years, 39 females) and prefrontal (PFC; n=58, mean age (SD) = 67.6 ({+/-}9.6) years, 30 females) regions using a HERMES sequence and analysed using OSPREYs pipeline. After correcting for gender and education, semi-partial correlations (rho) revealed no significant relationships between age and GABA+ or Glx concentrations in either the SM1 or PFC regions. Furthermore, through partial correlations (rho), after correcting for age, gender and education, we identified a significant negative relationship between SM1 Glx concentrations and go/no-go error rates, such that greater concentrations of Glx in the SM1 region were associated with greater accuracy on the go/no-go task. The null age-neurochemical results suggest that GABA+ and Glx may not uniformly decline during healthy ageing. This finding suggests that the relationship between older age and neurochemistry may be more nuanced than previously reported. In addition, our neurochemical-behavioural findings provide neurochemically-and-spatially specific evidence that SM1 Glx concentrations may be important for response inhibition. This result indicates a role for the glutamatergic system in supporting inhibition over the normal course of ageing.