Have you noticed in your training, that when a dog is in a high state of stress, he doesn’t process information clearly, like obedience commands that are well conditioned?
In the canine brain there are two key centers of activity that we must be concerned with; (1) The Limbic System and (2) The Cerebral Cortex. The Limbic System is concerned with emotion and the cerebral cortex with cognition, or thinking. Interestingly, activation of the limbic system inhibits activity in the cerebral cortex. Thus when the dog is in a high state of emotional aroural (i.e., stress), the thinking center will progressively shut down. He just phycically cannot think clearly.
This stress effect can come from outside the dog-trainer relationship, such as a threat trigger of the dog’s defensive instincts, or from within the relationship, as the trainer puts pressure on the dog in obedience. In the latter manifestation, the dog resorts to emotional behavior (avoidance, safety-seeking) in response to the limbic system taking over. If the trainer doesn’t recognize this, and presses the apparent "disobedience" with further pressure, it will create a vicious cycle, perhaps resulting in the dog resorting to aggression to halt the stress. The dog can no longer think and now simply reacts to reduce the stress.
An experienced trainer will recognize when stress is affecting the training session, and make an effort to change the training environment to remove the stress, and return the dog to a mood where he can think and process information.
One must be sure to slowly introduce stressors into the dog’s training. This will teach the dog how to simultaneously cope with stress and learn at the same time. By taking this process slowly, you will be able to create a trained response that can be reproduced under all manner of stress.