The effects of healthy ageing on gamma-aminobutyric acid (GABA) within primary motor cortex (M1) remain poorly understood. Studies have reported contrasting results, potentially due to limitations with the common assessment technique. The aim of the present study was to investigate the effect of healthy ageing on M1 GABA concentration and neurotransmission using a multimodal approach. Fifteen young and 16 older adults participated in this study. Magnetic resonance spectroscopy (MRS) was used to measure M1 GABA concentration. Single-pulse and threshold tracking paired-pulse transcranial magnetic stimulation (TMS) protocols were used to examine cortical silent period duration, short- and long-interval intracortical inhibition (SICI, LICI) and late cortical disinhibition (LCD). The reliability of TMS measures was examined with intra-class correlation coefficient analyses. SICI at 1 ms was reduced in older adults (15.13 ± 2.59%) compared to young (25.66 ± 1.44%, P = 0.002). However, there was no age-related effect for cortical silent period duration, SICI at 3 ms, LICI or LCD (all P > 0.66). The inter-session reliability of threshold tracking measures was good-to-excellent for both young (range 0.75 - 0.96) and older adults (range 0.88 - 0.93). Our findings indicate that extrasynaptic inhibition may be reduced with advancing age, whereas GABA concentration and synaptic inhibition are maintained. Furthermore, MRS and threshold tracking TMS provide valid and reliable assessment of M1 GABA concentration and neurotransmission respectively, in young and older adults.
- magnetic resonance spectroscopy
- transcranial magnetic stimulation
- gamma-aminobutyric acid
- intracortical inhibition
- Copyright © 2017, Journal of Neurophysiology