First identification of the causal link between 5-7 Hz oscillations in the cingulo-amygdala circuit and empathic response – ScienceDaily

A research team led by Dr. SHIN Hee-Sup at the Center for Cognition and Sociality (CCS) within the Institute for Basic Science (IBS) in Daejeon, South Korea, discovered the underlying neural mechanism that allows us to feel empathy. The group’s study of mice suggested that empathy is induced by synchronized neuronal oscillations in the right hemisphere of the brain, allowing the animals to perceive and share each other’s fear.

Empathy is the ability to perceive and understand another person’s emotions, such as joy, sadness, or fear. It is an essential function for human sociality and its impairment has been observed in numerous psychiatric and neurological disorders such as autism, schizophrenia and Alzheimer’s disease. The exact mechanisms in the brain that form the basis of empathy have not been identified, and few studies have been conducted to uncover its origins.

This ability to sense the feelings of others is not unique to humans, and its biological mechanisms are shared with other mammals, including rodents. “Observational anxiety,” a rodent model of emotional contagion, is the basic form of affective empathy. This model is well established and widely used to study the neurobiology of empathy. During the observational fear experiment, a “demonstrator” mouse receives an electric shock while an “observer” mouse watches from behind a transparent screen. When the observer mouse watches another animal receive a shock, it displays an immediate fear response, as shown by its freezing behavior. It is also known that the observer mouse can remember what it has experienced at a later point in time.

The CCS-IBS team led by Dr. SHIN Hee-Sup combined this observational fear model with optogenetic experiments to explore the origin of empathy. In particular, this study showed that the synchronized brain rhythms in multiple brain areas are essential for triggering empathy. In particular, synchronization between the anterior cingulate cortex (ACC) and basolateral amygdala (BLA) is unique to empathic fear from indirect exposure to the suffering of others, not fear from first-hand experience.

First, they showed that the reciprocal circuit between the ACC-BLA in the right hemisphere is essential for observed freezing behavior. When they optogenetically inhibited the ACC-BLA circuitry only in the right brain hemisphere, mice showed reduced observational freezing. On the other hand, mice were unaffected when only the left side was inhibited.

In addition, the researchers recorded an electroencephalogram (EEG) in the ACC and BLA. As a result, they found that brain rhythms in the 5-7 Hz range in the observer mice at the time they showed empathic freezing behavior selectively increased in ACC and BLA at the specific moment. On the other hand, the demonstrator mice that experienced the electroshock first hand showed an increase in the lower 3-5 Hz range only within the BLA but not in the ACC.

dr Shin explains: “Synchronous neural oscillations within the networks could enable improved communication between multiple brain areas for various cognitive and emotional functions. However, their causal relationship has rarely been proven.”

To test the causal relationship between 5-7 Hz rhythms and empathic behavior, the team conducted an experiment called “closed-loop manipulations,” which uses optogenetics to inhibit specific neural functions and the Brain waves can be monitored with EEG. Through the closed-loop experiment, they were able to selectively disrupt 5-7 Hz rhythms in the ACC-BLA circuit, which in turn resulted in significant impairment of observational anxiety-induced freezing during conditioning sessions. These results indicate that 5-7 Hz rhythms in the ACC-BLA circuit are causally involved in empathic behavior.

Therefore, the researchers hypothesized that hippocampal theta rhythms (4-12 Hz) might tune the synchronized activities within the ACC-BLA circuit. The hippocampal theta rhythm has been suggested to provide an oscillating framework that synchronizes activities between different brain areas. They selectively modulated the lower hippocampal theta region through optogenetic manipulations during observational anxiety. Following the changes in hippocampal theta output, the 5-7 Hz rhythm in the ACC-BLA circuits and empathic responses were bidirectionally modulated.

This study strongly suggests that hippocampus-dependent 5-7 Hz synchronized oscillations in the ACC-BLA specifically drive empathic responses in mice.

dr Hee-Sup Shin noted, “Given the universality of observed anxiety in mammals, it is reasonable to assume that a similar neural signature crucial for affective empathy can be found in humans and could be used to diagnose empathy disorders in people with psychiatric disorders Disorders to identify severe social deficits.” He added, “At the moment we don’t know how hippocampal theta rhythms control ACC-BLA rhythms. Future studies should address how multiple brain regions are simultaneously mobilized during observational anxiety. “

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