The locus coeruleus is an area of the brain which acts to regulate the level of activity in the brain. It is closely involved in the waking and sleeping cycle, and plays a number of other roles as well. The name of this structure literally means “the blue spot,” a reference to the bluish color it has in fresh brain tissue as a result of the presence of cells which contain higher concentrations of melanin.
This structure is located inside the brain stem, deep within the area known as the pons. The locus coeruleus is quite small, but has a long reach. Despite the fact that it is a tiny nubbin within the brain, its neurons connect with many areas of the brain, networking with areas responsible for sensory processing and many other activities. One could think of the locus coeruleus as a very long-limbed spider poised in the middle of the brain, with legs touching key areas.
Noradrenaline production is moderated by the locus coeruleus. This structure decides how much noradrenaline to produce and when, which determines how alert and awake the brain is. Production of noradrenaline occurs in response to sensory input which the locus coeruleus sorts through to determine the correct level of response. When someone glances at a dog, for example, the brain recognizes the animal as probably harmless, and it stays at a low level of excitation. A charging wolf, on the other hand, would trigger a surge of noradrenaline, a high state of alertness, and a stress response.
Stress and panic responses are an important part of what the locus coeruleus controls, but this structure is also involved in making memories, processing emotions, motivation, and attention. By moderating alertness levels, it can make the brain sluggish or more active, providing it with more energy to focus or overloading it in response to stress. The locus coeruleus neurons are constantly active, processing and sifting through information to identify relevant pieces which are used to regulate the brain's “speed,” so to speak.
The effects of the locus coeruleus can be seen in brain scans which measure brain activity. When a flood of noradrenaline is released, the brain lights up, often in multiple areas, as it kicks into high gear. When people are sluggish or resting and noradrenaline production is low, the brain is correspondingly inactive, with lower noradrenaline levels to excite it, keeping it in a less alert state.