From the time we choose whether to hit the snooze button or get up, we make countless decisions every day, but just how the brain manages this mundane task is still shrouded in mystery. Now, researchers at Oxford University have observed in detail the mechanism that lets fruit flies make decisions.
In a previous study, the team pinpointed a group of about 200 nerve cells in fruit fly brains that are active when the bugs are making decisions. Building on that, the researchers have now determined what's actually happening to these cells as the insects are gathering evidence in order to make a decision.
First, the fruit flies had been trained to associate a certain concentration of an odor with an electric shock. Once they'd learned that, the researchers would slowly ramp up the concentration of that odor towards the shock level, and see how long it took the fruit flies to anticipate a shock was coming and move away. When to move was the decision the researchers were studying.
The team found that tiny changes in the voltage of the surface of the neurons indicate that the fly is gathering evidence for each of the two choices. Eventually, these voltage changes would build up to a "hair-trigger point," and the nerve cell would give off a large electrical signal. This indicates that the fly has gathered enough evidence and made its decision.
"We have discovered a simple physical basis for a cognitive process," says Lukas Groschner, lead author of the study. "Our work suggests that there is an important analogue component to cognition. People sometimes compare the brain to a digital machine operating with sequences of impulses and silences. But much of what looks like silence is actually taken up by analogue computation."
The researchers identified that the key neurons all feature a genetic regulator molecule called FoxP, which is responsible for just how the evidence is added and retained. To test the role of this molecule, the team engineered flies with defective FoxP, and found that they take longer to make decisions. That's because these mutant insects produce too much of an "electric shock absorber," meaning the voltage of each neuron is less likely to change as the flies mull over the decision.
Of course, being a fruit fly test, this study doesn't necessarily scale directly to the human brain, but it's likely that a similar (albeit more complex) process is driving our decision-making. Humans do have FoxP genes, too, although we have four of them compared to the fruit fly's one. The researchers point out that two of them, FoxP1 and FoxP2, have been associated with cognitive development and intelligence in humans, suggesting there could be a link to decision-making.
"Fruit flies have an impressive record for making seemingly impenetrable biological problems tractable," says Gero Miesenböck, lead researcher on the project. "Research on fruit flies is now beginning to make significant inroads also into tough problems of cognitive science and psychology. I wouldn't be surprised if the long-term impact were similarly profound."
The research was published in the journal Cell.
Source: Oxford University
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