Prefrontal brain areas track subjective confidence.

People act and decide with varying confidence levels.

As they explore novel environments, people try options before fully committing to them; testing if that wooden bridge is solid enough, inspecting the tires of a car or trying a limited version of a product before buying it. Tracking and improving the confidence that we have on what surrounds us allows us to explore and exploit features of the environment successfully. Confidence is likely a major determinant of the economical decisions that we make, but the brain mechanisms involved remain poorly understood.

A suspensed wooden bridge. This is one of the situations where people seek to increase their confidence by first trying the bridge with the tip of their foot.Photo from Ivars Indāns released under the Creative Commons license.

Confidence in our actions is of particular interest because it is one of those psychological processes that is directed toward our inside states rather than the outside world. Confidence is introspective – it is how sure we are about our own knowledge of things. This is why it falls within the category of metacognitive processes. The subject is currently of high interest because experimental tricks were found to induce different confidence levels, both in human and non-human animals, and we are starting to be able to address the brain mechanisms involved1,2,3.

A recent study by De Martino and colleagues has looked into the brain areas in humans that might be related to confidence4. They focused on subjects making decisions between two items. They offered food and candies of different values to subjects. There are two phenomenons when people make these choices. First, there are occasions where the candies are pretty equal in terms of subjective value. This makes decisions harder to some degree. Other times, one of the candies is clearly preferred to the other, and subjects can choose with more ease. This is a classical setup that uses decision difficulty between two options. The authors introduced along this setup a measure of subjective confidence – meaning they asked people to do these choices and then evaluate on a scale whether or not they felt confident about their decision. Thus the experiment allows experimenters to tease apart decision difficulty due to the valuation process and subjective confidence that people can experience and report.


The ventromedial prefrontal cortex.Photo from finereach and Patrick J. Lynch released under the Creative Commons license.

The study identified two brain regions that might be related to some aspects of this task. First, the ventromedial prefrontal cortex had signals related to decision difficulty (how close the two options are valuated) and subjective confidence (which people reported using a scale). Another region, the right rostrolateral prefrontal cortex, has been found to be activated along with variations of subjective confidence, but not the difficulty of decisions. This means that the activity of this area tracked what people were feeling and experiencing in terms of confidence, but not necessarily in relation to how close the food items were in terms of value.

The authors of the study suggest that the ventromedial prefrontal cortex might be closely related to the decision or valuation process whereas the right rostrolateral prefrontal cortex might be a second-order area responsible to “read-out” confidence levels. Further work on these areas will allow us to completely test this hypothesis, which for now remains a plausible one.

References

1. Kiani R, Shadlen MN. (2009) Representation of Confidence Associated with a Decision by Neurons in the Parietal Cortex. Science vol. 324 (5928) pp. 759.

2. Kepecs A, Uchida N, Zariwala HA, Mainen ZF. (2008) Neural correlates, computation and behavioural impact of decision confidence. Nature 455:227-31.

3. Terrace HS, Son LK. (2009) Comparative metacognition. Current Opinion in Neurobiology 19:67-74. doi: 10.1016/j.conb.2009.06.004.

4. De Martino B, Fleming SM, Garrett N, Dolan RJ. (2012) Confidence in value-based choice. Nature Neuroscience doi: 10.1038/nn.3279.

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