Scientists at Stanford University in the United States conducted an experiment in which they made mice hallucinate by stimulating only a few neurons. This indicates the existence in mammals of a still unknown mechanism that prevents the occurrence of false perceptions in response to noise, that is, the random activity of nerve cells. This is reported by Science Alert.
In the course of the study, neuroscientists inserted two genes into the nerve cells of the visual cortex of rodents. One of the genes encoded a protein that activated a neuron whenever an infrared pulse hit the cell. The second gene is involved in the synthesis of a protein that emits green light when a neuron is activated. The scientists then removed a portion of the skull above the visual cortex, replacing it with a transparent material.
The rodents' visual system was stimulated with images of a horizontal or vertical line on a white background, and the researchers identified the neurons that are activated in each case. The mice are then trained to drink water when a vertical line appears on the screen. However, with a significant decrease in the contrast of the image, the animals ceased to distinguish lines and to drink. Using a special device, the researchers activated exactly those neurons that were responsible for the perception of the vertical line with infrared light, and the mice began to drink again, even if the image itself was absent.
It turned out that in order for the mice to form a false sensation that they were seeing a line, only 20 neurons had to be activated. Since the human brain has 20 billion neurons, it remains unclear how it suppresses hallucinations due to the random activity of many neuronal cells.