Age-related GABA- and glutamatergic differences in SMA during bimanual coordination

The Supplementary Motor Area (SMA) is key in bimanual coordination and higher order motor control. However, little is known about how excitatory and inhibitory neurometabolites in this region relate to motor performance, particularly across the adult lifespan. Using magnetic resonance spectroscopy (MRS), we investigated age-related differences in gamma-aminobutyric acid (GABA+) and glutamate + glutamine (Glx) levels in the SMA and their relationship with bimanual motor performance. Twenty-seven young and 25 older adults performed a Bimanual Tracking Task (BTT) during MRS acquisition. Results showed that young adults were more successful in performing the BTT than older adults (p < 0.001). Older adults revealed lower levels of both GABA+ (p < 0.05) and Glx (p < 0.001) than young adults during rest and task, but the GABA+/Glx ratio was not affected by age (p > 0.05). Also, we found no significant differences in neurometabolites between rest and task, hence no task-related modulations. A lower GABA+/Glx ratio (p < 0.05) during the task predicted better bimanual performance in older adults, whereas GABA+ and Glx at rest or during the task did not show a significant relationship with task performance (p > 0.05). These findings suggest that although neurometabolite concentrations decline with age, the relative inhibitory-excitatory balance in SMA may be preserved. Furthermore, a lower inhibitory tone appears to be critical for successful bimanual coordination in older adults.