Summary: Empathy is induced by synchronized neural oscillations in the right hemisphere of the brain, a new mouse study reveals.
Source: Institute of Basic Sciences
A research team led by Dr. SHIN Hee-Sup at the Center for Cognition and Sociality (CCS) within the Institute of Basic Sciences (IBS) in Daejeon, South Korea, discovered the neural mechanism under- underlying that allows us to feel empathy.
The group’s study in mice suggested that empathy is mediated by synchronized neural oscillations in the right hemisphere of the brain, which allows animals to perceive and share fear of the other.
Empathy is the ability that allows us to perceive and understand another individual’s emotions, such as joy, sadness or fear. It is an essential function for human sociality, and its impairment has been observed in many psychiatric and neurological disorders such as autism, schizophrenia and Alzheimer’s disease.
The precise 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 fear,” which is a rodent model of emotional contagion, is the basic form of affective empathy. This model is well established and is frequently used to study the neurobiology of empathy.
During the fear-watching experiment, a “demonstrator” mouse receives an electric shock, while an “watcher” mouse watches from behind a transparent screen. When witnessing another animal receiving a shock, the observing mouse displays an immediate fear response, as evidenced by its freezing behavior. The observing mouse is also known to be able to recall the experience later.
The CCS-IBS team led by Dr SHIN Hee-Sup combined this observational model of fear with optogenetic experiments to explore the origin of empathy. Notably, this study showed that synchronized brain rhythms across multiple brain areas are essential for triggering empathy.
In particular, the synchronization between the anterior cingulate cortex (ACC) and the basolateral amygdala (BLA) is unique to empathic fear through indirect exposure to others’ distress, not to fear through direct experience.
First, they showed that the reciprocal circuit between the ACC-BLA in the right hemisphere is essential for observational freezing behavior. When optogenetically inhibited ACC-BLA circuits only in the right brain, the mice showed a reduction in the observation freeze. In contrast, mice were unaffected when only the left side was inhibited.
Additionally, 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 selectively increased in the ACC and BLA at a specific time in the observer mice when they exhibited empathic freezing behavior.
On the other hand, demonstrator mice that experienced the electric shock first-hand showed an increase in the lower 3-5 Hz range only in the BLA but not in the ACC.
Dr Shin says: ‘Synchronous neural oscillations within networks could enable enhanced communications between multiple areas of the brain for various cognitive and emotional functions. However, their causal relationship has rarely been demonstrated.
To test the causal relationship between 5-7 Hz rhythms and empathic behavior, the team performed an experiment called “closed-loop manipulations,” which involves using optogenetics to inhibit specific neural functions and monitoring brain waves using EEG (Figure 2B).
Using the closed-loop experiment, they were able to selectively disrupt the 5–7 Hz rhythms in the ACC-BLA circuitry, which resulted in significant impairment of observation fear-induced freezing during conditioning sessions. These results indicate that 5-7 Hz rhythms in the ACC-BLA circuit are causally involved in empathic behaviors.
As such, the researchers hypothesized that hippocampal theta rhythms (4-12 Hz) might regulate synchronized activities within the ACC-BLA circuit. It has been suggested that the theta rhythm of the hippocampus provides an oscillatory framework that synchronizes activities between different areas of the brain.
They selectively modulated the lower hippocampal theta range by optogenetic manipulations during observational fear. Following changes in theta power of the hippocampus, the 5–7 Hz rhythm in ACC-BLA circuitry and empathic responses were bidirectionally modulated.
This study strongly indicates that hippocampus-dependent synchronized 5–7 Hz oscillations in ACC-BLA specifically drive empathic responses in mice.
Dr. Hee-Sup Shin remarked, “Given the universality of observational fear in mammals, it is reasonable to assume that a similar neural signature critical for affective empathy can be found in the humans and could be used to identify empathy dysfunction in humans with psychiatric disorders involving severe social deficits.
He added: “At this time, 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 fear.
About this Empathy Research News
Author: William Suh
Source: Institute of Basic Sciences
Contact: William Suh – Institute of Basic Sciences
Image: Image is in public domain
Original research: Access closed.
“Hemispherically lateralized rhythmic oscillations in the cingulate-amygdala circuit drive affective empathy in mice” by SHIN Hee-Sup et al. neuron
Hemispherically lateralized rhythmic oscillations in the cingulate-amygdala circuit drive affective empathy in mice
- The lateralized rACC-rBLA circuit is responsible for observational fear (OF)
- The 5–7 Hz oscillations in rACC and rBLA increase during OF
- 5–7 Hz oscillations in rACC and rBLA are causally involved in OF
- Hippocampus type 2 theta bidirectionally modulates ACC-BLA theta and OF
Observational fear, a form of emotional contagion, is considered a fundamental form of affective empathy. However, the neural process engaged at the precise moment when socially acquired information elicits an emotional response remains elusive.
Here, we show that reciprocal projections between the anterior cingulate cortex (ACC) and basolateral amygdala (BLA) in the right hemisphere are critical for observational fear, and neural oscillations at 5–7 Hz were selectively increased in these areas at the start of the observation freeze. .
A closed-loop perturbation demonstrated the causal relationship between 5–7 Hz oscillations in the cingulo-amygdala circuit and observational fear responses. Increase/decrease in theta power induced by optogenetic manipulation of hippocampal theta rhythm bidirectionally modulated observational fear.
Together, these results indicate that hippocampal-dependent 5–7 Hz oscillations in the right hemisphere cinguloamygdala circuit are the essential component of cognitive processing that drives empathic fear, but not freezing, in general.
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