Differential glutamate modulation in the anterior mid-cingulate cortex of healthy adults during inhibitory motor control utilizing a novel interleaved baseline control condition: a ¹H fMRS study.

Response inhibition, or the ability to suppress "pre-potent" behavioral responses, is subserved by both motor and inhibitory control processes and linked to the anterior mid-cingulate cortex (aMCC). We utilized an adapted Go/No-Go paradigm combined with proton functional magnetic resonance spectroscopy (1H fMRS) of the dACC to investigate differences in glutamate level between an All-Go (non-selective motor responding) and Go/No-Go (selective motor responding) condition, both compared to a no-response condition. This allowed disambiguation of the excitatory neurochemistry underlying motor vs. inhibitory control processes. 1H fMRS (midline dACC; 4.1 cm3) was acquired in 15 participants at 3T during non-selective (response to 100% of trials) vs. selective motor responding epochs [response to 80% of trials (20% inhibition)]. Each motor response mode was conducted as a separate task run (random order) with interleaved epochs matched for visual stimuli (timing and physical size) but without motor responses. Glutamate was quantified across motor responding modes (selective vs. non-selective), motor demands (present vs. absent), and their interaction. dACC glutamate was significantly higher (3.7%) during non-selective motor responding relative to interleaved periods without motor responding. aMCC glutamate was not significantly different during the selective vs. periods of no-response. A task order effect showed higher glutamate among participants who (randomly) completed the non-selective task run first. Non-selective motor responding drove increased aMCC glutamate relative to periods without motor responding whereas the effect was absent for the selective responding mode. Our findings suggest that generalized motor control processes increased aMCC excitatory neuromodulation drive, whereas the additional engagement of inhibitory control processes did not change the excitatory neuromodulation drive.