Research shows that a person processes any signals that enter the brain in different ways. Even if the signal is the same. The reaction to a stimulus is formed after information about it enters the cerebral cortex, and other levels of perception do not affect it so much.

Scientists have long been researching the nature of perception and brain responses. They found that the effect of an external stimulus on the areas of this organ that process it depends on the state of the neurons, which is constantly changing. However, it has not yet been possible to understand how and why these changes occur, whether they are chaotic or are influenced by many unknown factors.

A group of researchers from the Max Planck Institute for Cognitive and Neuroscience (MPI CBS) in Germany found that the sensitivity of neurons changes when information about an external stimulus reaches the cerebral cortex. Scientists conducted an experiment in which 33 men participated. Small shocks were applied to their forearms, which triggered a reaction in the somatosensory cortex after 20 milliseconds. Then the reaction of the brain was measured.

Observations have shown that some nerve cells in the primary somatosensory cortex become more or less excitable in response. And only at this moment it is determined how exactly the brain will react to the stimulus. The mechanism of work is described in the Journal of Neuroscience.

“Neurons are always active, even if there is no external influence on a person. Thus, the system is never completely stationary, ”explains Stephanie Tilman, an MPI CBS graduate student and first author of the study.

It turns out that changes in the excitability of the cerebral cortex do not occur by chance: its level at a particular moment is affected by how excitable it was earlier. Scientists call this continuous-time dependence or long-term autocorrelation.

The authors suggest that perception is also influenced by constantly incoming information about the state of the body: about heartbeat, digestion, respiration, position in space, temperature, and thoughts. In addition, neurons are active even if the neurons are isolated from any signals. “The dynamics of internal processes is related to the excitability of the systems and, therefore, the response to stimuli,” says Stephanie.