This is a fascinating article that suggests that learning under conditions of stress follows a biphasic curve similar to many drugs and herbs. Meaning that the same “substance” has a stimulating effect in small doses and and inhibitory effect in large doses. I thought about looking for research in this area because of research about flow triggers. One of the best triggers for flow is to be challenged just enough to go beyond what you are already capable of doing but not so much that you experience overwhelming frustration. This concept is also known in the field of instructional design under the name cognitive load theory. It is well established that working memory is very limited. When learning something new, one is generally filling most of their working memory with pre-requisite knowledge. Just the right amount of new information for the learner at any given level will have a beneficial stimulating effect on learning while too much will cause an overload and inhibit learning.