Like humans, fruit flies think before they act. The process involves coordinating a small group of about 200 neurons and a protein called FoxP.
According to previous models of human decision-making, when presented with clear evidence, we make decisions speedily; likewise, a lack of evidence prolongs the process, since you need to gather up information first. “Freedom of action from automatic impulses is considered a hallmark of cognition or intelligence,” Oxford’s Gero Miesenböck says in a news release. “Fruit flies have a surprising mental capacity that has previously been unrecognized.”
To help understand the neural mechanisms underlying the process in flies, Miesenböck and colleagues put Drosophila fruit flies in some tricky situations, having them make a decision when supporting evidence isn't clear. That meant filling small, narrow chambers with a scent-emitting compound called methylcyclohexanol (MCH); flies were trained to avoid potent concentrations of this odor. The researchers measured the time between a fly’s entry into and exit out of the chamber. When MCH was at the prohibited concentration, flies quickly exited. But when the concentration was watered down, the flies spent longer inside trying to deduce if MCH was, in fact, at the potent level.
When the two ends of the chamber had very different concentrations of MCH, the flies were able to easily choose between them. But the harder it got to make this assessment -- that is, as the concentrations of the two ends got closer -- the longer the flies’ reaction times. Turns out, flies don’t simply act instinctively or impulsively. Rather, they appear to accumulate information before committing to a choice.
When the team looked for single gene defects that made flies indecisive for difficult decisions, they found that FoxP -- a protein that helps regulate development -- was involved in the timing and accuracy of decision-making processes in the fly brain. Mutations in the gene that codes for FoxP caused information to take longer to accumulate before the fly could reach a decision: Compared with normal flies, these mutant flies took longer to decide when odors were harder to distinguish.
The FoxP gene is active for about 200 neurons (out of 200,000 in the fly brain). “Before a decision is made, brain circuits collect information like a bucket collects water. Once the accumulated information has risen to a certain level, the decision is triggered,” study author Shamik DasGupta of Oxford explains. “When FoxP is defective, either the flow of information into the bucket is reduced to a trickle, or the bucket has sprung a leak.” They become indecisive.
In humans, defects in FoxP are associated with difficulties in cognitive development, motor control, and language.
The work was published in Science this week.
Image: Greg Smolonski