During the test, respondents thought that everything was stacked against them
Paranoia, often referred to as an irrational or overinflated sense of anxiety, stems from a very rational ability to maintain composure in a chaotic environment. Now scientists have found out which part of the brain is responsible for the appearance of this mental disorder.
To better understand why some people's brains respond more strongly to shadows than others, a team of researchers led by Yale University psychiatrists Praveen Suthaharan and Summer Thompson analyzed the results of a simple test conducted on a group of male rhesus monkeys and human volunteers.
The test consisted of choosing a symbol that gave a chance to receive a reward — food for monkeys and points for people. Different symbols gave different chances of success, so the subject was given the opportunity to choose one of three symbols on the screen and find out which one was most likely to bring a reward.
Just at the moment when the subjects thought that they found a pattern after passing half the test, the test results were reversed: the luckiest symbol paid rewards less often, and the unluckiest one became the optimal choice.
“So participants must figure out what the best goal is, and when there is a perceptible change in the environment, the participant must find a new best goal,” explained psychologist Steve Chang.
Six of the 20 macaques had previously undergone neurological procedures in separate studies that targeted either their dorsal thalamic nuclei — an area thought to play an important role in planning, abstract thinking and organization — or an area of the prefrontal cortex involved in decision making. And human volunteers had to fill out a questionnaire on a thinking scale to assess their level of paranoia, and be re-surveyed to determine signs of any depression.
After analyzing the behavior of monkeys and people and comparing the results with survey data, The team was able to determine which damaged areas of the brain might affect the monkeys' ability to calmly navigate a changing gaming environment.
“Not only did we use data in which monkeys and humans performed the same task, but we also applied the same computational analysis to both sets of data,” says psychiatrist Philip Corlett.
The findings showed that both the magnocellular mediodorsal thalamus (MDmc) in the dorsal thalamic nucleus and areas of the orbitofrontal cortex (known as Walker areas 11, 13, and 14) differentially affected the monkey's behavior after the test switch.
For those with mobility problems, the sudden loss of reward had little effect on their decisions. The monkeys continued to press the buttons containing the «winning» ticket with reckless abandon.
Those with damaged MDmc exhibited exactly the opposite behavior, switching back and forth even after they discovered that the new symbol paid a reward. as if they suspected that the system was rigged against them personally.
This was similar to behavior observed in people whose survey responses indicated higher levels of paranoia.
Although delusional Ideation and paranoid behavior are clearly complex behaviors that involve a variety of thinking patterns, identifying a link between one specific area and inconsistent decision making could provide the basis for future research that could lead to the development of new treatments or help better understand how some activities increase the risk of psychosis.
“Perhaps in the future we can use this to find new ways to combat paranoia in people,” concludes Chang.