Motor training (MT) elicits formation of motor memories in the human primary motor cortex. Observing another individual perform motor training (Action Observation, AO) also results in formation of motor memories in M1. AO enhances motor training effects (MT+AO) on the formation of motor memories. Possible underlying mechanisms include long-term potentiation (LTP), a process influenced by N-methyl-D-aspartate (NMDA) receptor activation, gamma-aminobutyric acid (GABA), norepinephrine (NE), dopamine and acetylcholine (Ach), taking place at the confluence of inputs from PMv over the primary motor cortex (M1).