Newswise — Avoiding our fears might be influenced by a specific cluster of neurons within a visual brain area, as per recent findings from the University of Tokyo. The study revealed that in fruit fly brains, these neurons secrete a substance called tachykinin, which seems to govern the fly's movements in order to evade potential threats. Since fruit fly brains can serve as a useful model for larger mammals, this investigation may enhance our comprehension of human responses to frightening situations and phobias. Subsequently, the researchers aim to ascertain the integration of these neurons within the brain's broader circuitry, enabling them to ultimately chart how fear regulates vision.
Do you close your eyes while watching horror films? Or does the sight of a spider prompt you to quickly retreat? It's a common occurrence for both humans and animals to avoid looking at things that frighten us. But what exactly causes us to divert our gaze from the objects of our fear? Scientists have discovered that this behavior may be attributed to a cluster of neurons in the brain that modulates visual perception when experiencing fear.
Assistant Professor Masato Tsuji from the University of Tokyo's Department of Biological Sciences explained, "Through our research on Drosophila (fruit flies), we have uncovered a neuronal mechanism that governs visual avoidance in response to fear. Interestingly, it seems that a compact group of 20-30 neurons plays a crucial role in regulating vision during fear states. Given that fear impacts visual perception in various animal species, including humans, it is plausible that this mechanism also operates in humans."
Using bursts of air as a simulated physical threat, the research team observed that fruit flies exhibited an increase in walking speed upon being subjected to these puffs. Additionally, when given the option, the flies actively chose a route that did not involve encountering the puffs, indicating their perception of them as potential threats. Subsequently, the researchers introduced a small black object, similar in size to a spider, positioned at a 60-degree angle either to the right or left of the flies. In isolation, the object did not elicit any noticeable behavioral changes. However, when presented after the bursts of air, the flies averted their gaze from the object and adjusted their movement to position it behind them.
In order to delve into the molecular mechanism behind this aversive behavior, the researchers proceeded to manipulate the activity of specific neurons by using mutated flies. Despite the mutated flies retaining their visual and motor capabilities and still displaying an avoidance response towards the bursts of air, they no longer exhibited the same fear-driven behavior of visually avoiding the object. This suggests that the altered activity of these neurons plays a crucial role in generating the fearful response responsible for visual aversion.
Tsuji stated, "These findings indicate that the cluster of neurons responsible for releasing tachykinin is essential for triggering visual aversion. Interestingly, during our observation of the flies' neuronal activity, we made a surprising discovery: the activity exhibited an oscillatory pattern, resembling a wave-like motion of activity fluctuations. Typically, neurons operate by simply increasing their activity levels, and reports of oscillatory activity are quite rare in fruit flies. This is mainly because, until recently, the technology required to detect such small-scale and rapid oscillations didn't exist."
By employing genetically encoded calcium indicators, the researchers were able to induce the illumination of the flies' neurons upon activation. Leveraging the advancements in imaging techniques, they were then able to observe the dynamic, fluctuating pattern of light emitted by the neurons. Previously, this intricate pattern had gone unnoticed, as it was averaged out and overlooked by earlier methodologies.
Moving forward, the research team aims to unravel the integration of these neurons within the wider circuitry of the brain. While these neurons are located within a recognized visual region of the brain, the specific sources from which they receive inputs and the destinations to which they transmit signals, thereby regulating visual escape responses to perceived threats, remain unknown to the researchers. By investigating these connections, the team hopes to gain a comprehensive understanding of how these neurons contribute to the overall mechanism of visual avoidance.
Tsuji expressed their team's next objective, stating, "Our upcoming objective is to elucidate the mechanisms involved in the transmission of visual information within the brain. By doing so, our ultimate aim is to construct a comprehensive circuit diagram that illustrates how fear modulates vision." Tsuji further speculated, "In the future, our findings could potentially offer valuable insights for the treatment of psychiatric disorders characterized by heightened fear responses, including anxiety disorders and phobias." The research holds promise for potentially guiding therapeutic approaches in addressing these conditions.
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