Dr. Rollin McCraty, Director of Research for the Institute of HeartMath, explains why feelings of anxiety drive up the level of mental noise to such
a pitch that it overloads the circuits the brain needs for paying attention, learning, focusing, and remembering. "When students are anxious about their test performance, their brain ceases to function efficiently. They can look at a test question and literally not see certain words, become confused or miss the meaning of the question. They can even miss seeing entire questions on the page!"

Dr. McCraty says that the key to understanding how anxiety inhibits cognitive and physical performance lies in understanding how emotions affect the rhythmic activity in the nervous system.

Feelings like frustration, anger, and anxiety cause the neural activity in the two branches of the autonomic nervous system to get out of sync. This in turn affects the synchronized activity in the brain, disrupting our ability to think clearly. On the other hand, uplifting feelings such as appreciation lead to increased harmony and synchronization in the brain and nervous system, which facilitate our ability to think clearly.

A surprising finding of the Institute's research is the important role the heart plays in determining how "in sync" we are. Dr. McCraty explains: "The heart puts out a powerful, rhythmic signal that the brain responds to. Nerve impulses originating in the heart dramatically affect how we think, perceive, and perform. In a way, we could say that the heart and brain 'talk' to one another—and together they set the rhythms for the entire nervous system and body. In fact, the heart sends more signals to the brain than the brain sends to the heart! The signals it sends—whether harmonious or chaotic—can make all the difference in our performance. Chaotic activity in the nervous system leads to what is called 'cortical inhibition.' Our reactions are slowed and we cannot think clearly. The more refined mental processes required – such as abstract reasoning or comprehending the deeper meaning of what is being read – are especially affected."