This year marks the golden jubilee of The Exorcist, the iconic American supernatural horror film that left countless people terrified, so much so that they covered their eyes during numerous scenes. The act of avoiding frightening or disturbing visual stimuli is a shared experience among both humans and animals. However, the underlying reason for averting our gaze from these fearful things has long intrigued researchers. Now, a group of Japanese scientists has found some interesting clues in the brains of fruit flies.
The researchers discovered a neuronal process that governs visual aversion in the brains of fruit flies when they experience fear. This mechanism involves a specific cluster of 20-30 neurons responsible for regulating their vision during fearful situations. The researchers assume that since fear affects vision across species, including humans, this mechanism must be present in all those species.
As per their study published in Nature, the researchers employed bursts of air to create a sense of physical threat, observing that the fruit flies' walking speed increased when subjected to these puffs and gradually returned to its baseline level afterwards. This response indicated that the flies perceived the air bursts as threatening or, at the very least, preferred to steer clear of them. To further explore this aversion behaviour, the team introduced a small black object, similar to the size of a spider, positioned either 60 degrees to the left or right of the fly. Interestingly, the object alone did not prompt any notable changes in behaviour. However, when presented with the puffs of air, the flies avoided looking at the object and positioned themselves to keep the object behind them.
Seeking to delve into the molecular mechanisms underlying this aversion response, the researchers introduced CRISPR-generated neuropeptide-null mutant flies, with altered activity in specific neurons. Despite maintaining their visual and motor abilities and still managing to avoid the air puffs, the mutated flies did not display the same fear-driven reaction when it came to visually avoiding the black object. This finding indicated a crucial link between the identified neurons and the flies' aversion behaviour towards perceived threats.
The researchers found that a cluster of neurons that releases the chemical tachykinin was necessary for activating visual aversion. The team is currently investigating how these neurons integrate into the broader brain circuitry. Despite identifying these neurons within a recognised visual region of the brain, the researchers are yet to determine the sources of inputs they receive and the targets they transmit to, which ultimately regulate visual responses, guiding the avoidance of perceived threatening objects. Once they unravel the mechanisms of visual information transmission in the brain, they will be able to construct a comprehensive circuit diagram illustrating how fear influences vision. This discovery holds the potential to offer insights into the treatment of psychiatric disorders associated with exaggerated fear, such as anxiety disorders and phobias in humans.