Task-Related Neurotransmitter Dynamics in the Visual Cortex: A Proof-of-Concept Time-Resolved fMRS Study Using a...

The neurochemical mechanisms underlying sustained visual processing, particularly in the early visual cortex, remain unclear. Earlier research has primarily focused on higher-order frontal and parietal regions, yet emerging evidence suggests that the visual cortex may contribute to early-stage sustained visual processing. Functional magnetic resonance spectroscopy (fMRS) provides a unique opportunity to detect task-induced changes in neurometabolite concentrations, enabling dynamic assessment of neurometabolic processes. In this proof-of-concept study, five participants, all female, with a mean age of 26.5 ± 4.0 years, underwent three fMRS sessions on consecutive days using a sustained vigilance paradigm targeting the visual cortex. Time-resolved analyses were applied to investigate task-evoked neurotransmitter changes during sustained vigilance with differing visual input demands. Our results provide preliminary evidence that the Gabor-based vigilance condition was associated with an increase in glutamate-glutamine (Glx) levels relative to the comparison condition, while glutathione, N-acetylaspartate, and creatine levels remained stable. Importantly, traditional time-averaged analysis did not detect significant task effects, highlighting the potential sensitivity of time-resolved analysis. The temporal profile of Glx responses suggested gradual increases during sustained task engagement, although precise latency estimates should be interpreted cautiously given the temporal resolution of the method. Furthermore, exploratory correlation analyses indicated a positive association between Glx concentrations and behavioral performance, suggesting a potential association between visual cortical Glx dynamics and task performance during sustained vigilance. Overall, these preliminary findings suggest that dynamic Glx changes in the visual cortex may reflect combined visual processing demands and attentional-related engagement during sustained vigilance. Importantly, these changes should not be attributed to attentional modulation alone. These findings provide preliminary support for the feasibility of time-resolved fMRS at clinically accessible field strengths for detecting dynamic glutamatergic changes and highlight the potential utility of fMRS in elucidating task-evoked neurotransmitter dynamics. Future studies with larger samples and more controlled experimental designs will be required to further dissociate sensory processing and attention-related contributions.