Neurons in the lateral prefrontal cortex, a region of the brain found to be abnormal in psychosis, are also important in helping people distinguish between reality and imagination, according to a recent study published in the journal Nature Communications.
The researchers looked at how the brain codes visual information in reality compared to abstract information based on memories. They also investigated how those differences are distributed across neurons in the lateral prefrontal cortex region of the brain.
“You can look at my shirt, and then if I move out of your vision, even with your eyes open you can still see the color of my shirt in your mind,” said Dr. Julio Martinez-Trujillo, principal investigator and professor at the University of Western Ontario’s Schulich School of Medicine & Dentistry.
“That is what we call working memory representations or short-term memory representations — they are abstract, they are imaginary and they don’t exist in reality, but in our minds. Real objects in our visual field, we call perceptual representations. We are trying to determine whether there are neurons in the brain that can signal to a person whether a representation is real or imaginary.”
For the study, participants completed two tasks: one in which they had to report the direction of movement of a cloud of dots they could see on a computer screen; and one in which they had to report the cloud direction a few seconds after it disappeared based on a memory of the image.
The researchers found that neurons in the lateral prefrontal cortex encoded perceived and memorized information to varying degrees and in different combinations of strength.
“We might have expected that the neurons that are active when we perceive a visual object are the same ones that memorize it; or, on the contrary, that one group of neurons perceives the object and a completely different group memorizes it; but instead, we found that all of the above are true to a certain extent,” said first author Dr. Diego Mendoza-Halliday, postdoctoral researcher at the Massachusetts Institute of Technology (MIT).
“We have perception neurons, memory neurons, and also neurons that do both things.”
The lateral prefrontal cortex has been shown to be dysfunctional in individuals with schizophrenia, a severe mental disorder characterized by hallucinations and/or delusions. Yet, until now, researchers have not been able to identify the source of this dysfunction.
Using machine-learning, the research team developed a computer algorithm that could read out the pattern of neurons firing in the prefrontal cortex and reliably determine whether a participant was looking at a cloud of dots in real-time or remembering one they had seen before.
Martinez-Trujillo hopes that by identifying the specific neurons responsible for distinguishing between reality and imagination, they might be better able to treat disorders like schizophrenia that cause patients to confuse what’s real and what isn’t.
“I would argue that schizophrenia is not a neurochemical disorder of the whole brain,” said Martinez-Trujillo. “It is only a neurochemical disorder in specific parts of the brain.”
Currently, medications for these disorders change the neurochemistry in the entire brain, often causing unintended side-effects. By targeting only the specific neurons responsible for these disturbances, the researchers hope to one day minimize these side-effects.
Source: University of Western Ontario