Neurons specialized in completing images make us fall into the trap of optical illusions. If they work poorly, anomalous perceptions arise.
Fans of optical illusions will be happy to know that the neurons responsible for these deceptions of perception have been found. A group of Californian scientists has identified the cells involved in the creation of a particular type of optical illusion, those that lead us to see the outlines of an object that is not actually appearing before our eyes.
Understanding how they work, and how the entire circuit of which they are part acts, is more than a simple curiosity: it will help to better understand the false sensory perceptions typical of schizophrenia. The study was published on Nature Neuroscience.
Do you see it, the white square?
The neurons in question were called “IC–encoder neurons” (where IC stands for illusory contours“illusory contours”) and are responsible for completing recurring patterns, the brain’s tendency to rely on previous experiences to complete a visual perception if sensory information is incomplete or missing. Scientists at the University of California, Berkeley observed the electrical activity of these cells in the brains of mice subjected to famous optical illusions, such as those of the Kanizsa triangle, or square (below).
When scientists activated these neurons, which are located in the primary visual cortex, with an optogenetic technique, essentially “controlling them with light”, the cells generated the same brain activation patterns that are observed in the presence of an optical illusion.
A ping pong of commands
The processing of the final optical illusions is the result of a dialogue between these specialized neurons and the higher visual areas, responsible for perceiving important information about the context in which the image is inserted. The chain of commands goes from top to bottom: the representation arises in the higher visual areas, which then send it to the primary visual cortex, where the IC-encoder neurons physically carry out the instruction to see something that is not actually there.
Taking the example of the square, the higher visual areas interpret the central part of the image as a white square and tell the IC-encoder neurons to see a white square.
We have room to maneuver
A circuit that works with this exchange of information gives back the idea of vision as a process and not – simply – a passive acquisition of information. If illusory perceptions such as optical illusions are the result of a construction, of calculations that influence what we ultimately see, then it means that we have more room to manipulate the final product of these processes.
It could be important in cases where visual representations of non-existent objects arise randomly and not in response to stimuli, as in schizophrenia, a disorder characterized by false sensory perceptions, including visual hallucinations.
Understanding how these representations arise will help us better understand how to treat them.
