Our Brains Want Maximum Rewards, Linked to Memories of Choices, New Study Finds

How our brains make decisions has now been answered via a math model.
Farah Saleem

Neuroscientists from the University of Geneva (UNIGE), Switzerland, in partnership with Harvard Medical School have figured out an answer to the 'optimal choice strategy.' How do our brains make choices? This was answered using a mathematical model. 


Our brains constantly make choices throughout the day, but how does this really work? The research notes two types of decision-making: perceptual (Do I have time to cross the road before that car comes nearer?) and value-based: (Do I want to eat apples or apricots?)

When dealing with value-based decisions, the researchers found that our brains make decisions based not on the true value of the possible choices, but on the differences between them. This means that it is seeking maximum rewards. Why does it do this? This new research investigates.

New research

The research notes that when the difference in choices is high, the decision is made quickly. But when they are close, this choice becomes more difficult and takes more time.

A simple math model, designed by UNIGE's researcher, Satohiro Tajima, highlights the optimal strategy when we are faced with two choices.

The brain sums up the values that are associated with the memories attached to the two choices. If we have more positive experiences, i.e., memories associated with the choice, then the decision is made when this difference comes to a "threshold value." This, in turn, determines the time the decision takes to make. 

The model then helps make quick decisions because the values associated with the two choices are far apart. However, a key difference is noted when the choices have the same value. It takes the brain more time to reach a decision threshold.

The reason? The brain needs more time to draw on memories to reach a decision threshold and cannot make a quick decision. 

More than two choices

The study also delves into choices that are more than two. For each possibility, maximum rewards are sought, and positive memories associated with each choice are taken into consideration. 

"The first step is exactly the same as when making a binary choice: we amass the memories for each choice so we can estimate their combined value," explains Alexandre Pouget, a professor at UNIGE.

Math model

Using a mathematical model, "the decision rests on the difference between the cumulative value of each choice and the average value of the accumulated values over all the choices," the study states.

If the different choices had similar values, it would take a longer decision-making time, because the values of the choices are now interfering with one another.  

"Making a simple choice can take 300 milliseconds, but a complicated choice sometimes lasts a lifetime," notes the Pouget.

This explains why sometimes our choices can take not just hours, but sometimes years. This study not only shows that the brain is doing some amazing calculations based upon the difference in values and the memories we associate with them, but it also sheds some light on how some choices in life need more time and thought. We need to feel that a particular choice has maximum rewards associated with it.

The researchers hope to continue the study by focusing on memories with each choice, and how the brain processes decision-making regarding unknown information, without any memories associated with it. 

The full findings are published in Nature Neuroscience.

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