How rodents make decisions
Exploring how the brain generates a feeling of confidence Research by Champalimaud Foundation scientist reveals surprising results
The confidence that we have in taking a decision is considered to be one of our principal characteristics as humans: which way we choose when we arrive at a crossroad depends on the confidence that we have in each alternative. A new study carried out by Zachary Mainen, Coordinator of the Champalimaud Neuroscience Programme, questions this human exclusivity by showing that rats can also show varying levels of confidence in making decisions.
These surprising results, obtained at the Cold Spring Harbor Laboratory, USA, were recently published in Nature(*).
Mainen and colleagues trained laboratory rats to engage in decisions of different difficulty. Because rats excel at olfaction, this was achieved by repeatedly presenting them with odours composed of mixtures of two chemicals and asking them to determine which component was stronger in order to receive a small reward.
According to Mainen, “by precisely varying the exact mixture of components, it was possible to manipulate the difficulty of the decision and therefore the animals’ predicted level of uncertainty. This task is akin to asking a human whether a particular blend of blue and green colors is more blue or more green. Confidence is typically highest when the blend is mostly green or mostly blue. Uncertainty is highest when the blend contains nearly equal amounts of each color.”
The team recorded signals from individual neurons localized in the orbitofrontal cortex, an area of the brain common to both rats and humans. While the rodents were put to the test of distinguishing smells, the team found a correlation between velocity of “firing” of the cells and the level of indecision experienced by the rats in choosing the smells.
“These neurons seem to have been registering, after the rat made its decision, how uncertain the animal was that it was about to receive its desired reward,” Dr. Mainen explained. “We tested several alternative explanations but the best explanation for the neural activity we observed was that these neurons were signaling the confidence of the animal about its decisions.”
The team also went on to show that in uncertain situations the rats prefer to abstain from making a decision for a few moments and then perform the test again, rather than making an incorrect decision.
Mainen stated that “our results suggest that confidence estimation is not a complex function specific to humans but a core component of the process of decision-making probably found throughout the animal kingdom. Future studies of this kind may illuminate the question of how we form an intuitive sense of the solidity of a belief, how we distinguish fact from fiction itself.”
The Champalimaud Neuroscience Programme is dedicated to the study of the cellular and molecular bases of behaviour. The Programme, based in the Gulbenkian Institute of Science (IGC), was launched in 2007 and contains five research teams working at the cutting-edge of neuroscience research.
* Kepecs, Uchida, Zariwala and Mainen (2008), Neural correlates, computation and behavioural impact of decision making, Nature advance online publication 10 August 2008
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