Does the creation of memory involve mRNAs crossing the synaptic gap?
I have never heard of this pathway. Memory is usually assoiciated with synaptic plasticity by ‘Long-term potentiation’ (LTP), which has glutamate as a neurotransmitter. Neuroscience Exploring the brain (Bear, et al,. 2007), has a pretty good explanation of this process, if you're interrested. Motor patterns have more mechanisms than LTP, and are not as well understood.