Asian Scientist Magazine (Aug. 02, 2023) — Scientists in Japan have located a specific cluster of neurons that regulate vision when we are afraid. The study was recently published in Nature Communications.
Prior animal studies have revealed some insights into how fear can cause us to avert our gaze, but the precise brain structure and mechanism responsible for it remained less understood. To look for answers, researchers from the University of Tokyo, turned to Drosophila melanogaster or the common fruit fly. These tiny winged creatures have a sophisticated and well-studied visual system that offers a great analogy for larger mammals, both in its anatomy and how it influences their behavior.
“We discovered a neuronal mechanism by which fear regulates visual aversion in the brains of Drosophila. It appears that a single cluster of 20-30 neurons regulates vision when in a state of fear,” said Assistant Professor Masato Tsuji, Department of Biological Sciences at the University of Tokyo. “Since fear affects vision across animal species, including humans, the mechanism we found may be active in humans as well.”
In the behavioral experiments, the researchers set up an LED arena around the fruit fly subjects, placed on an air-supported foam ball. Using air puffs for simulating a physical threat, they observed a notable increase in the flies’ walking speed—a primary sign of feeling threatened in these insects. The flies also showed a preference for choosing directions where there were no air puffs.
In order to understand the molecular mechanism behind this visual aversion, the researchers used mutated flies that were unable to release certain brain chemicals called tachykinin. The results demonstrated that although flies without tachykinin retained their visual and motor functions, they did not exhibit the same fearful response of avoiding the objects they perceive as threat.
“This suggested that the cluster of neurons which releases the chemical tachykinin was necessary for activating visual aversion,” said Tsuji. “When monitoring the flies’ neuronal activity, we were surprised to find that it occurred through an oscillatory pattern, i.e., the activity went up and down similar to a wave. Neurons typically function by just increasing their activity levels, and reports of oscillating activity are particularly rare in fruit flies because up until recently the technology to detect this at such a small and fast scale didn’t exist.”
The researchers gave genetically encoded calcium indicators to fruit flies, which enabled the activated neurons to shine bright, a response that occurred solely in the presence of air puffs.
Given the fruit flies’ significance in studying various biological processes, including learning and behavior, the researchers believe that this study could help us better understand human responses to scary situations and phobias. Next, Tsuji’s team is eager to explore how these neurons integrate into the brain’s overall circuitry. While they have identified the neurons’ location, the mystery lies in mapping out the precise reception and transmission of brain signals which regulate the visual avoidance of potentially dangerous objects.
“Our next goal is to uncover how visual information is transmitted within the brain, so that we can ultimately draw a complete circuit diagram of how fear regulates vision,” said Tsuji. “One day, our discovery might perhaps provide a clue to help with the treatment of psychiatric disorders stemming from exaggerated fear, such as anxiety disorders and phobias.”
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Source: University of Tokyo ; Image: Shutterstock
The article can be found at Threat gates visual aversion via theta activity in Tachykinergic neurons.
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