How Your Brain Makes Decisions Impacts How It Evaluates (Mis)Information

Gabriel A. Silva
7 min readMay 25, 2021
True or False? Your brain has to assess risk and arrive at a decision. Getty Images.

How do you judge if something is factual? How do you make the decision to accept a statement as being true, versus it being misleading or flat out wrong? What are the calculations going on in your brain that lead to such a decision? And how do they determine who — and what — you trust? In today’s world, reliable information for some is the misinformation of others.

Your brain is constantly sampling its environment and evaluating risk. It has to combine real time sensory information and what it consumes with internal past experiences, biases, and lessons learned in order to update your mental model of the outside world. This is an ever changing and dynamic process that allows you to adapt to the events, people, and situations around you.

Imagine you are on a game show. The game show host starts by giving you a secret word you will need decide how to use later. You are then given exactly five minutes to evaluate a total stranger through a sound proof window. They are assigned the same task. You can see them and they can see you but you can’t communicate in any direct way. To the best of your ability you quickly form an opinion of them. How their appearance strikes you, what their body language is, what you think they might think of you. You arrive at a judgment of this person you’ve never met given the rules of the game in the face of rather incomplete information.

The two of you are then put into separate rooms, where each of you are ‘interrogated’ by a third contestant neither of you have previously met. You immediately size them up too. The job of this third individual is to get both of you to give up your secret words. They can use any verbal tricks they can come up with to try get the two of you to give it up. They can lie, tell the truth, even tell you that they’ve struck a deal with your counterpart in the other room. If they’re successful, they will win a large sum of prize money. But if you and the other player keep your mouths shut and don’t say anything, each of you will win an equal amount of money. However, if you give up your secret word and the other content doesn’t, you win half the prize money and they get nothing. Of course, if it goes the other way around, you walk away with nothing. How would you play this out? Would you trust that they would keep their mouth shut or do you think you can cheat them? How much do you trust the interrogator? How much value do you place on them — how slick are they — at convincing you that other contestant is keeping their lips sealed when in fact they haven’t?

This game is a version of the Prisoner’s Dilemma, a classic research tool within Game Theory, which is the the formal study of interpersonal and strategic relations among multiple agents, such as human beings. The Trust Game and its variations is another well studied tool used to understand how humans make decisions about how to trust, and how they perceive and judge trustworthiness in others.

Research in a number of related fields is uncovering how humans assess risk, make decisions, and assign value and trust under different situations. One of these fields is behavioral economics, which is the study of social, psychological, cognitive, and emotional considerations and factors associated with decision making and risk assessment.

For example, risk calculations and the eventual decisions an individual makes vary depending on whether they are engaged in a scenario driven by purely logical rules, such as playing a game against a computer, or whether they are playing against other unpredictable humans. Trusting someone puts you in a vulnerable position. Deciding to trust someone you don’t know carries with it an amount of implicit risk. It turns out humans hate to be cheated and swindled. There is a psychological risk to being betrayed that has a real cognitive cost. This is separate from the more logical, dispassionate, and purely financial risk associated with losing something of value, such as the risk associated with losing money. This ‘betrayal aversion’ is significant and the cognitive cost associated with it so high that it affects how risk is perceived and judged.

The relatively new field of neuroeconomics brings together empirical and quantitative neuroscience methods such as functional magnetic resonance imaging (fMRI) to study the anatomy and physiology responsible for how the brain makes decisions. fMRI allows researchers to image and measure what parts of the brain are working extra hard during an assigned task, such as solving a math or word problem — or playing the Trust Game. By combining fMRI information across different brain regions in combination with other molecular and cognitive experiments, scientists can build a picture about how the brain integrates various sources of information, including past experiences, to assign trust, calculate risk and make decisions.

For example, the neuropeptide hormone oxytocin, synthesized in a part of the brain called the hypothalamus — which is where the brain exerts control over the endocrine system — seems to affect and increase how much trust we place in others, independent of whether that trust is deserved or not. It is a physiological chemical effect. The same hormone is known to modulate social behavior in humans and animals to strengthen maternal bonding attachment. So in a way it makes sense that it have such an effect on how you trust others.

Equally important, although less studied to date, is how the context in which risk and decisions are evaluated affect the outcome. Context matters. The same set of factual considerations in different contexts may necessitate putting more or less emphasis on some aspect of a risk calculation versus another. For example, analogous but distinct from contextual influences on how the brain makes decisions, the effect context can have on perception has been well studied for a long time. The Ebbinghaus illusion is a classical example. In the figure below, both yellow dots are the exact same size, even though they don’t look like it. Yet despite how long this perceptual effect has been studied, the neural and perceptual mechanisms responsible for this effect however, continue to be debated. Science is rarely black or white, but rather a constantly evolving shade of gray.

The Ebbinghaus illusion. Gabriel A. Silva

How Misinformation Affects the Brain

In this current information-rich environment everyone is perpetually exposed to a constant stream of ever changing never ending information from many sources. By the sheer necessity imposed by the volume of information alone, individuals are forced to decide what sources to trust and what not to trust. Leaving aside the important consideration of the factual accuracy of the information being consumed, from a cognitive perspective how and when that information is presented is just as important as what is being presented.

The brain seems to have a degree of neurobiological ‘bias’ independent of the content of the information, i.e. regardless of ideology, past experiences, or learned biases. This presents a challenge if the information being offered up as factual turns out to be incorrect or misleading, because there is growing research that suggests the damage may be done and hard to correct.

When information is accepted by the brain, it can be surprisingly difficult to change or update memories later presented when presented with alternative facts. So if incorrect information was presented first, it can be surprisingly difficult to change or update those memories if corrected facts came second. This in turn, can directly affect and influence an individual’s judgment and reasoning about the event or topic the information relates to.

This occurs even when there is an acknowledgment and understanding that the original information was intentionally or unintentionally incorrect. What’s even more amazing is that this effect can occur even when individuals are warned and know ahead of time that they will be exposed to and receiving misinformation. Scientists call this ‘continued influence effect of misinformation (CIEM).

From a cognitive and neurobiological perspective, on-going research by a number of groups is attempting to understand why and how this happens. Scientist are beginning to understand how different regions of the brain interact to produce this effect.

When the brain is presented with corrected or updated information, it struggles to integrate and reconcile it with the original (possible) misinformation that it learned first. It has a hard time replacing it with updated facts, even if the individual knows and understands that’s what needs to happen. Interestingly, it seems that while the brain can indeed encode updated information and corrections to the original misinformation, it has a harder time removing and forgetting the incorrect older stuff. It struggles to inhibit the misinformation it learned first, and ends up in a state of quasi-confusion from competing memories, which in turn affect judgment.

With the anticipated proliferation of potentially misleading technologies, such as deep fake videos, the implications of this kind of research are paramount. Deep fake videos are fabricated videos enhanced using artificial intelligence that show individuals saying (and eventually soon doing) things they never did. The uses of deep fakes are not all bad. For example, they have a use in movie making and editing. But their abuse in spreading misinformation is a serious concern. Jordan Peele made a deep fake of former President Obama as a public service announcement warning about the potential misleading and dangerous use of deep fakes that has been seen millions of times. (A word of caution: There is some mild swearing in the video.)

On a positive note though, there is some initial evidence that deep fake videos may not be any more powerful than misleading static images or text. But viewed the other way, this implies that different mediums all have the potential to exert an equally impactful negative effect.

The amount and rate of information and misinformation people are exposed too will likely only continue increasing for the foreseeable future. This has significant sociological, economical, health, and policy implications. Understanding how the brain processes and reacts to all that information is a critical tool in managing this phenomenon.

This article was originally published on You can check out this and other pieces written by the author on Forbes here.

Gabriel A. Silva

Professor of Bioengineering and Neurosciences, University of California San Diego