Is the amount of learning modulated by reward transmitters? The human brain is a signal processing system. Input streams contain sensory, motor, reward and possibly more signals mixed. I wonder if neuro transmitters associated with reward increase or decrease memorization of those streams. That would result in a tendency to memorize streams co-occurring with high reward over those co-occurring with low reward. Thus, attractors would settle for better streams and we would perform actions  optimizing the reward.
The effect of dopamine signaling is one of the areas where computational neuroscience has provided insight into brain mechanisms, specifically via Reinforcement Learning (RL) models.

Based off this paper and PHD thesis from Dan Rasmussen, this first began with this publication from Schultz showing that dopamine acts as a reward signaler. From the abstract:


  Dopamine neurons are activated by rewarding events that are better
  than predicted, remain uninfluenced by events that are as good as
  predicted, and are depressed by events that are worse than predicted.
  By signaling rewards according to a prediction error, dopamine
  responses have the formal characteristics of a teaching signal
  postulated by reinforcement learning theories.


To answer your question directly, it does seem the speed/plasticity of learning is modulated by dopamine neurons.