Researchers have identified the brain centre associated with responses to rapid temperature change. The researchers have located a brain circuit in fruit flies that selectively responds to rapid thermal change, priming behaviour for escape.
This leads to the likelihood that animals are more likely to react to rapid rather than slow environmental change. The work was undertaken using fruit flies (Drosophila) and it was found that fruit flies use their antennae to steer away from dangerous heat. The research carries wider implications for other animals, including humans.
In undertaking their study, the Northwestern University scientists have identified a brain pathway responsible for rapid-threat detection. This leads lead scientist Marco Gallio to conclude: “Animals are more likely to react to rapid rather than slow environmental change.”
Fruit flies are used as a model for such experiments due to their relative simplicity. The flies operate to the basic decision-making principles as in an animal, but they have a fraction of the number of neurons (100,000) than humans have (roughly 100 billion). As a well-studied model organism for biological research, flies also are useful subjects because of the pre-existing tools to study fly neurons and behaviour.
There are two types of responses to external stimuli in the brain: Some neurons respond to a stimulus like light or temperature with very persistent activity. Other neurons fire just at the beginning, like when a light turns on, and then their activity is gone. The researchers were interested in the significance of these short-lived responses.
To explore how flies respond to rapid change, the researchers used a high-resolution camera to observe flies navigating different temperature environments. When flies encounter a rapid heat front, they always produce a U-turn away from it.
By using this technique, the researchers discovered that flies always responded in cases of rapid temperature change, but not for slow change.
The researchers also identified a circuit in the fly brain that responds only to rapid temperature change (more than 0.2 degrees Celsius per second). Much like light-ON cells of the visual system, these neurons fired at the beginning of rapid heating and then went quiet.
This led to the assessment that heat-ON responses correlate with the rate of temperature change. This allows flies to anticipate dangerous thermal conditions and prepare to escape. This was demonstrated when the researchers experimentally inactivated these neurons and the flies escaped less promptly.
The scientists were subsequently able to reconstruct the full circuit from sensory neurons all the way down to the centres that produce movement.
Gallio hypothesizes that the results are broadly generalizable, especially because he sees it play out in humans, whether someone is entering a room that’s a different temperature or getting into a hot shower. He said these neurons seem to be able to sense something others do not — they seem to be able to anticipate the future. This finding paves the way for further research.
The findings appear in the journal Nature Communications. The research is titled “Rapid threat assessment in the Drosophila thermosensory system.”
