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By weaving together expectations and information gleaned from the senses, the brain creates a story about the outside world. “The brain is a guessing machine, trying at each moment of time to guess what is out there,” says computational neuroscientist Peggy Seriès.

Guesses just slightly off — like mistaking a smile for a smirk — rarely cause harm. But guessing gone seriously awry may play a part in mental illnesses such as schizophrenia, autism and even anxiety disorders, Seriès and other neuroscientists suspect. They say that a mathematical expression known as Bayes’ theorem — which quantifies how prior expectations can be combined with current evidence — may provide novel insights into pernicious mental problems that have so far defied explanation. Evidence based on previous experience, known as a “prior,” is essential to arriving at a good answer, Bayes argued.

People with schizophrenia differ from “normal people” when tying together their expectations with what their senses detect. They often suffer from hallucinations and delusions, debilitating symptoms that arise when lines between reality and imagination blur. These departures from reality could arise from differences in how people integrate new evidence with previous beliefs. People with schizophrenia don’t fall for certain visual illusions that trick most people. To complicate matters, the opposite can be true, too, says neuropsychologist Chris Frith of the Wellcome Trust Centre for Neuroimaging at University College London. “In this case, their prior is too weak, but in other cases, their prior is too strong,” he says.


In a recent study, healthy people and those who recently began experiencing psychosis, a symptom of schizophrenia, were shown confusing shadowy black-and-white images. Participants then saw color versions of the images that were easier to interpret. When shown the black-and-white images again, people with early psychosis were better at identifying the images, suggesting that they used their prior knowledge — the color pictures — to truly “see” the images. For people without psychosis, the color images weren’t as much help. That difference suggests that the way people with schizophrenia balance past knowledge and present observations is distinct from the behavior of people without the disorder. Sometimes the balance tips too far — in either direction.

“Not seeing”…

In a talk at the annual Computational and Systems Neuroscience meeting in February in Salt Lake City, Seriès described the results of a different visual test: A small group of people with schizophrenia had to describe which way a series of dots were moving on a screen. The dots moved in some directions more frequently than others — a statistical feature that let the scientists see how well people could learn to predict the dots’ directions. The 11 people with schizophrenia seemed just as good at learning which way the dots were likely to move as the 10 people without, Seriès said. In this situation, people with schizophrenia seemed able to learn priors just fine. But when another trick was added, a split between the two groups emerged. Sometimes, the dots were almost impossible to see, and sometimes, there were no dots at all. People with schizophrenia were less likely to claim that they saw dots when the screen was blank. Perhaps they didn’t hallucinate dots because of the medication they were on, Seriès says. In fact, very early results from unmedicated people with schizophrenia suggest that they actually see dots that aren’t there more than healthy volunteers. (or perhaps the scientists are prejudiced against people tagged as “sick”)

Preliminary results so far on schizophrenia are sparse and occasionally conflicting, Seriès admits. (1)

Seeing what is there.

Seeing what is not there.

The brain this…

The brain that…

More and more often, we fail to understand the actual problem. More and more often we speak about the brain and how it creates issues in understanding the cosmos. More and more often, the brain looks like an obstacle in our attempt to connect with reality rather than a helpful tool…

Pascal said it a long time ago.

The heart.

Listen to the heart…