Research articleGlutamatergic metabolites are associated with visual plasticity in humans

- First study of visual plasticity using multi-modal neuroimaging in humans.
- Used a fMRI paradigm with high frequency stimulation to study visual plasticity.
- Used MRS to measure glutamate (Glu), glutamine (Gln), and GABA.
- LTP-like visual plasticity was observed, similar to past animal and human studies.
- Resting visual cortical Glu, Gln, and GABA predict visual plasticity in humans.

Long-term potentiation (LTP) is a basic cellular mechanism underlying learning and memory. LTP-like plasticity in the visual cortex can be induced by high frequency visual stimulation in rodents and humans. Since glutamate plays a fundamental role in LTP, this study investigated if visual cortical glutamate and glutamine levels, measured by proton magnetic resonance spectroscopy (MRS), relate to visual plasticity in humans. Since plasticity requires a delicate excitation and inhibition balance, GABA was also explored. Eighteen healthy participants completed MRS and a visual fMRI paradigm. Results revealed enhanced fMRI activations after high frequency visual stimulation, suggesting visual plasticity occurred. Higher activations were associated with higher resting glutamine levels after family wise error-correction. Exploratory analyses revealed that higher resting glutamate and GABA levels were associated with visual plasticity, suggesting there may be a critical excitation-inhibition balance necessary for experience dependent plasticity. This is the first empirical evidence that resting glutamine levels and potentially glutamate and GABA levels are associated with visual plasticity in humans.