What is the role of the locus coeruleus in stress?

The locus coeruleus has many connections to other parts of the brain, particularly areas that bring in and process sensory information (information from sight, hearing, smell, taste, and touch). The locus coeruleus secretes norepinephrine and stimulates other brain centers to do the same. It is like the pacemaker (meaning it controls the tempo) of the brain. Thus, it increases arousal (heightened awareness, alertness) and vigilance (watchfulness, carefulness), and adjusts (modulates) the action of the autonomic nervous system, which includes the SNS. The autonomic nervous system regulates blood flow, heart rate, blood pressure, and breathing (respiration). It can also temporarily shut down the gastrointestinal (GI) and sexual systems until the crisis is over. These initial reactions, to get our blood flowing, heart pumping, and muscles energized, occur very quickly and automatically.

How do the connections in the brain work in stress?

The HPA axis and the locus coeruleus systems are linked through the hypothalamus and an area of the brain known as the limbic system. The limbic system is the control area for emotion and the processing area for memory. These linkages are critical. For example, if you see the bushes rustling, your locus coeruleus immediately starts things (the stress response) rolling. However, when you see that it is not a mountain lion but a golden retriever in the bushes, your memory of the tameness of the dog will turn off the stress response. Similarly, if a person is nervous before a public-speaking engagement and the first minute or two goes well, this happy feeling will turn down the activity of the locus coeruleus. These internal adjustments are why experienced public speakers often start off with a joke. It's as much to calm themselves (if the joke goes well) as it is to entertain you.

The connections also include the endogenous (within the body) opiate (opium-like) system and the reward (dopamine) system. Thereby, during stress, pain is reduced and an extremely happy feeling (euphoria) may result. These connections partially account for "runner's high" and have a great deal to do with why we like roller coasters and scary movies.

Here's how the connections work. The limbic system performs an emotional analysis and memory review of the information provided by the senses. Then, the multiplicity of connections allows us to determine whether the current stress is

• one that has been mastered in the past and successfully adapted to,
• not a threat at all, or
• a clear and present danger.

All of this internal activity must occur in milliseconds, and it does.