The mystery of the enigmatic "blue spot" in the brain has been solved

Scientists from the Allen Institute have created a detailed map of the locus coeruleus — a small cluster of neurons in the brain that controls the stress response. The results of a large-scale study published in the journal Nature have overturned established theories about how this region works and revealed the structure of the longest nerve cell ever measured.

For a long time, neuroscientists believed that this tiny region functioned as a single loudspeaker, simultaneously broadcasting noradrenaline signals — a neurotransmitter that triggers the stress response and affects attention — to all parts of the brain. However, the authors of the paper used imaging methods, genetic tools, and behavioral experiments in mice to demonstrate that the system actually operates as a targeted postal network. Cells from the upper part of the cluster send impulses to the cerebral cortex, handling learning processes during decision-making. At the same time, neurons from the lower zone communicate with the brainstem and spinal cord, controlling the animal's overall engagement with what is happening.

During the precise mapping of the organ, which included scanning nearly 35,000 neurons, the scientists discovered unique physical characteristics of these cells. It turned out that the average length of their axons — long projections that transmit electrical signals — is approximately 35 centimeters. But one of the projections reached an incredible 70.32 centimeters, making it the longest single nerve cell ever measured in a mouse. This giant projection supplies noradrenaline to vast areas of the cortex, selectively bypassing the cerebellum and other regions.

"This cell supplies noradrenaline to a very large volume of the cerebral cortex, which is extremely atypical for the organ. Most neurons are more specific in choosing their targets," noted study co-author, biologist Jeremiah Cohen.

The biologists also drew a parallel between noradrenaline and dopamine — another key neurotransmitter. According to the researchers, these two systems together form a platform for learning, enabling the brain to acquire multiple complex and abstract concepts simultaneously. Noradrenaline is critically important for regulating mood and attention. It is precisely this system that popular medications for depression, anxiety, and attention deficit hyperactivity disorder (ADHD) target.

Furthermore, neurons of the locus coeruleus are the first to deteriorate in the development of Alzheimer's disease. The discovery of the cluster's architecture paves the way for the creation of targeted therapies: in the future, doctors will be able to selectively act on specific areas of the brain without flooding the entire system and avoiding side effects.