Fruit flies offer clues to how brains make reward-based decisions (VIDEO)
Caption
A behavior called matching -- where choices between options are divided in proportion to the rewards received -- is pervasive in the animal kingdom, but it was unclear how the brain carried out this value-based decision-making. Researchers had previously proposed a theory for how that might happen, but the idea hadn’t been tested in the real world. Now, a team of Janelia researchers has confirmed that the proposed theory works. Experiments show that fruit flies can make decisions based on their expectations about the likelihood of a reward. The team also pinpointed the site in the fly brain where these value adjustments are made, enabling them to directly test this theory on the level of neural circuits. To test this behavior in flies, the researchers designed an experiment where a single fly enters one arm of a symmetrical Y-shaped arena. Odors are pumped into the other two arms of the Y. The fly chooses to follow one odor or the other and is rewarded – in this case by having its sugar-sensing neurons activated – but with different probabilities: One odor might translate into a reward 80 percent of the time, while the other odor might yield a reward 20 percent of the time. The first video shows the fly during three trials. The fly begins a trial in one arm of the Y filled with clean odor-free air and can choose between two other arms that have been randomly assigned different odors, denoted by the different colors. Once a fly makes its way up one of the odorized arms and crosses into the reward zone, a reward is provided according to the reward contingencies of the task by activating the fly’s sugar-sensing neurons. The Y then resets so that the arm that was just chosen is filled with clean air and the other two arms are now randomly assigned odors. In this video, the reward is provided on the third trial, when the fly chooses the orange odor. In the second video, the odor that the fly is moving in is denoted by the names on the bottom left. When the fly is in the clean air, both odors are grayed out. When the fly is an arm that contains 3-octanol, OCT is lit up in green and when the fly is in an arm that contains 4-methylcyclohexanol, MCH is lit up in yellow. Flies in this case are rewarded after choosing OCT. The researchers found that the fly learned to expect the rewards in the same proportions they were presented and then made its choice based on those expectations. These actions give the matching behavior its name: 80 percent of the time, the fly chose the odor that gives 80 percent of the rewards. And 20 percent of the time, it chose the odor that yields 20 percent of the rewards.
Credit
Rajagopalan et al.
Usage Restrictions
Please use caption and credit provided
License
Original content