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

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 the large-scale study, published in the journal Nature, overturned established theories about how this region works and revealed the structure of the longest nerve cell.

For a long time, neuroscientists were convinced that this tiny region functions 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 study, armed with imaging methods, genetic tools, and behavioral experiments on mice, proved that the system is far more complex and operates as a targeted postal network. Cells from the upper part of the cluster send targeted impulses to the cerebral cortex, supporting learning processes during decision-making. Neurons from the lower zone, by contrast, communicate with the brainstem and spinal cord, regulating the animal's overall engagement with what is happening.

During the painstaking mapping effort, which involved scanning nearly 35,000 neurons, the researchers discovered astonishing physical characteristics of these cells. The average length of their axons — the long projections that transmit electrical signals — was approximately 35 centimeters. But the real sensation was one particular projection: it stretched an incredible 70.32 centimeters, becoming the longest single nerve cell ever measured in a mouse. This giant axon supplies noradrenaline to vast areas of the cortex while 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," emphasized the study's co-author, biologist Jeremiah Cohen.

The scientists also drew a parallel between noradrenaline and dopamine — another key neurotransmitter. In their view, the two systems jointly form a platform for learning, allowing the brain to acquire multiple complex and abstract concepts simultaneously. Noradrenaline is critically important for mood and attention regulation — it is precisely this system that is targeted by widely used medications for depression, anxiety, and attention deficit hyperactivity disorder (ADHD).

The discovery gains particular significance from the fact that locus coeruleus neurons are the first to deteriorate during the development of Alzheimer's disease. Deciphering the cluster's architecture paves the way for creating precision therapies: in the future, doctors may be able to selectively target specific areas of the brain without flooding the entire system, minimizing side effects.