Done using brain scans and repeat tasks correlated to various parts of motor learning and human learning behaviors, the researchers examined various neurotransmitters (primarily GABA) and their role in how receptive we are to learning. There were lots of ins and outs to the study but some of the key findings were:

• Increased GABA means increased neural plasticity.
• Increased GABA concentrations have increased functional effects on the brain.

Overall, "the responsiveness of the GABA system to modulation has a strong relationship with motor learning." GABA is a calming neurotransmitter involved in nervous-system function. Magnesium is associated with feelings of relaxation and a general sense of calm. L-theanine is an amino acid which has a calming, grounding effect on the body and mind without making you feel drowsy.

https://www.sciencedirect.com/science/article/pii/S0960982211001254