n most cases, the brain induces motion via the muscles - when the brain isn't involved, it's some form of reflex.
Well trained aikido isn't a reflex, it is a conditioned response - stuff comes out without you having to think about it - kinda like Pavlov's dogs responding to a bell.
A conditioned response is when Gunny yells "Do you git me!?! You yell "Sir, yes, sir!"
It is more correct to say that it is a conditioned reflex -- which is the same as Pavlov's dogs. Salivation is a reflex that can be cued by systematic association. Aiki involves a set of simple spinal reflexes that are provoked/evoked/coordinated by correct conditioning. IMO