There are two kinds of stress. Eustress and distress. Eustress is the "happy" stress and distress is exactly as it sounds, "sad stress" We all live with stress and a little stress is good for learning. Too much stress, however is bad even if it's good.
The Limbic System and the Cerebral Cortex
The Limbic System is responsible for experiencing and expressing emotions, which can directly affect behavior. It is the canine’s emotional center.
The Cerebral Cortex produces learning, memory, attention, perceptual awareness and problem-solving. It is the canine’s thought center.
The cerebral cortex and the limbic system have an important relationship with each other. While one of these two systems are stimulated or in use, the other system’s function is inhibited.
Example: When a canine is slightly stressed you can still access their cognitive abilities before the brain defaults to the limbic system.
Example: When the canine starts to become overstressed, his brain starts to shift into the limbic system and he becomes enthralled in an emotional response. He is no longer able to respond because the cognitive ability has shut down.