A new study – led in part by Prof. Rony Paz and Dr. Tamar Reitich-Stolero from Weizmann’s Brain Sciences Department – has uncovered brain mechanisms that make us more sensitive to losses during learning and decision-making. Excessive or inappropriate activation of these mechanisms may even help explain behaviors seen in people with anxiety disorders and PTSD.
In the new study, Weizmann Institute researchers joined forces with Ichilov Medical Center physicians to probe the neural mechanisms of learning and memory under the risk of loss. In the first part of the study, participants dealt with two types of trials while the activity of single neurons in their brains was being recorded: Some trials offered the chance to gain points, while others involved the risk of losing points. Sounds and shapes indicated the type of trial and the odds for gain or loss. Over time, participants learned which options consistently led to better outcomes.
“Even so, performance was different in the two types of trials,” Reitich-Stolero says. “In the loss tasks, participants sometimes ignored the optimal choice and kept desperately searching for strategies that might prevent losses altogether, not just minimize the risk of loss. In contrast, in the gain tasks they stuck with the best option once they had learned it and were less likely to look for creative solutions.”
To understand the neural mechanisms behind this behavior, the researchers monitored the activity of hundreds of single neurons across different brain regions. They found higher levels of neural noise in the amygdala when participants faced potential losses and when they searched for new strategies to avoid loss, with models showing that the noise was linked to feelings of uncertainty. “When exploratory behaviour becomes uncontrolled, people can get stuck in a constant search for better options – a hallmark for anxiety disorders,” says Reitich-Stolero.
The second part of the study examined the ability to generalize. Participants heard tones they had previously learned to associate with gains or losses, as well as new tones that were similar or different. The researchers found that participants tended to overgeneralize in the loss situation, treating a broader range of new tones as “familiar” and risky when they were similar to a tone previously associated with losses.
“When generalization gets out of control, it can be harmful,” Paz explains. “It’s a great defense mechanism, but when it’s overactive, as in PTSD, it can lead to stress, anxiety, and depression.”
”While the amygdala’s role in fear and anxiety has been known for years, only recently have we been able to study decision-making in humans at such high resolution,” Paz notes. “Now we can better understand what goes wrong in various disorders – and point the way to improved treatments for post-trauma and mood disorders.”