Often dismissed as an irrational or exaggerated sense of worry, paranoia stems from a very rational ability to maintain one’s sanity in a chaotic environment.
The ability to adapt quickly can keep us alive when circumstances change. In the extreme, however, delusional beliefs about the bad intentions of others can be socially isolating and rob people of the ability to maintain healthy relationships and hold down jobs.
To better understand why some brains figuratively jump into shadows more than others, a team of researchers led by Yale University psychiatrists Praveen Suthaharan and Summer Thompson analyzed the results of a simple test on a group of male rhesus macaque monkeys and human volunteers.
The test, called the probabilistic reversal learning (PRL) task, revolved around choosing a symbol for a chance of reward—food for the monkeys and points for the humans.
Different symbols provided different chances of success, so when given a choice of three on the screen, the subject was given the opportunity to learn which symbol was most likely to win a reward.
Just when subjects thought they had it all figured out halfway through the test runs, the results of the trial reversed, with the luckiest symbol paying rewards less often and the unluckiest symbol now becoming the optimal choice.
“So participants have to figure out what the best goal is, and when there is a perceived change in the environment, the participant then has to find a new best goal,” says Yale psychologist Steve Chang.
Six of the 20 macaques had undergone neurological surgery earlier in separate studies that affected either their dorsal thalamic nuclei – an area thought to play a role in planning, abstract thinking and organization – or an area in their prefrontal cortex involved in decision-making . .
Human volunteers, on the other hand, were asked to complete a thought scale questionnaire to assess their level of paranoia and a second survey to determine signs of any depression.
By analyzing the behavior of the monkeys and humans before and after the change, and comparing the results with survey results, the team was able to assess which areas of the brain might influence the monkey’s ability to move coolly in a volatile game 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 Yale psychiatrist Philip Corlett.
The data suggest that both the magnocellular mediodorsal thalamus (MDmc) in the dorsal thalamic nucleus and locations in the orbitofrontal cortex (known as Walker’s areas 11, 13, and 14) all influenced the monkey’s test-switch behavior in subtly different ways.
The sudden loss of reward among those who had blocked Walker areas had little effect on their decision to switch. The monkeys continued to tap what they thought was the “winning” ticket with reckless abandon.
Those whose MDmc was damaged showed quite the opposite behavior, switching back and forth even after discovering a new “high chance” symbol, paying rewards, almost as if they suspected the system was rigged against them personally.
This was similar to the behavior seen in people with survey responses indicating higher levels of paranoia.
While delusions and acts of paranoia are undoubtedly complicated behaviors involving different mindsets and different areas of the brain, tracking the boundary between one particular area and volatile decision-making could inform future studies that could lead to new therapies or help us better understand how some actions increase the risk of psychosis.
“Maybe we can use this to find new ways to reduce paranoia in people,” Chang says.
This research was published in Cell messages.