Using observations in mice, led primarily by first author and PhD student José Antonio González Parra and supervised by Dr. Arnau Busquets, the research team was able to determine the mechanisms involved in how the brain makes decisions based on indirect associations between different stimuli. That is, instead of directly associating a specific stimulus with a rewarding or aversive situation, the brain establishes connections between two or more stimuli. As Dr. Busquets explains, "The project aims to understand how the brain enables us to make decisions based on indirect relationships between stimuli in our environment."

In this context, the mice were subjected to various behavioral tests. They were trained to associate one smell-banana-with a sweet taste, and another smell-almond-with a salty taste. Later, a negative stimulus was associated with the smell of banana. From that point on, the mice rejected the sweet taste, which was linked to the banana smell and thus carried a negative connotation. In other words, "they formed an indirect association between the sweet taste and the aversive stimulus through its link to a specific smell," explains Busquets.

The Role of the Amygdala

Using genetic techniques delivered via viral vectors, the researchers were able to observe which areas of the mice's brains were activated throughout the process of encoding and consolidating the associations. They found that the amygdala, a brain region associated with responses such as fear and anxiety and involved in certain mental disorders like psychosis and PTSD, was activated when the mice linked olfactory and taste stimuli.

At the same time, they identified other brain areas that were also involved and interacted with the amygdala. Thanks to imaging techniques, they were able to establish a connection between these areas and a part of the cerebral cortex. "We have identified a brain circuit that controls associations between stimuli and allows for these indirect associations," says Dr. Busquets. They also confirmed that if amygdala activity was inhibited while the mice were exposed to the stimuli, the animals were unable to form these indirect associations.

As Dr. Arnau Busquets explains, the researchers believe that the brain circuits involved in decision-making processes in humans are similar to those in mice. Therefore, the data obtained in this newly published study could be relevant for treating certain mental disorders linked to amygdala activity. "Alterations in these indirect associations form the basis of various mental disorders," he adds. "Understanding the brain circuits involved in these complex cognitive processes can help us design therapeutic strategies for humans." In this sense, future approaches could include brain stimulation or modulation of activity in these areas in people with PTSD or psychotic symptoms.

The research, published in the Journal of Personality and Social Psychology, shows that people with a low IQ (the lowest 2.5% of the population) make forecasting errors that are more than twice as inaccurate as those made by people with a high IQ (the top 2.5% of the population).

The research used data from a nationally representative sample of people over 50 in England (English Longitudinal Study of Ageing ELSA), assessing their ability to predict their own life expectancy.

Individuals were asked to predict their probability of living to certain ages, and these estimates were compared with the probabilities taken from Office for National Statistics life tables (a demographic tool used to analyse death rates and calculate life expectancies at various ages). The study controlled for differences in lifestyle, health, and genetic longevity.

By analyzing participants' scores on a variety of cognitive tests, as well as genetic markers linked to intelligence and educational success, Chris Dawson, Professor of Economics and Behavioural Science at the University of Bath, showed that smarter individuals tend to have more accurate beliefs about uncertain future events -- they are more skilled at assessing probability.

Individuals with a higher IQ are significantly better at forecasting, making fewer errors (both positive and negative) and showing more consistent judgement compared to those with a lower IQ.

"Accurately assessing the probability of good and bad things happening to us is central to good decision-making," said Professor Dawson. "Almost all decisions we make, whether it's starting a business, investing, crossing the road, choosing who to date, all require probabilistic assessments.

"IQ is already known to predict health, wealth, income, occupational status and educational attainment and this research highlights one possible channel through which people with a lower IQ do worse on all these outcomes."

Professor Dawson suggests that explicitly stating probability estimates on information relating to health and finance for example, rather than relying on individuals to do their own calculations, could help people prone to forecasting errors to make more informed, accurate decisions.

"I found that certain genetic traits linked to intelligence and education are associated with more accurate predictions, suggesting that lower cognitive ability may causally contribute to the formation of more biased assessments," said Professor Dawson. "Probability estimation is the most important aspect of decision-making and people who struggle with this are at a distinct disadvantage.

"Expectations about the future shape how households make critical decisions -- like how much to save, when to retire, or whether to invest. Poorly calibrated expectations can lead to bad financial decisions, and reduced economic welfare, which can adversely affect national growth."