Summary: A new study identified a brain circuit responsible for rapid, unified response to threats in animals, a phenomenon observed in fish schools and mammal herds.
The research, focused on synchronized immobility in pairs of mice, paves the way for an improved understanding of social communication in general, which is often compromised in neuropsychiatric disorders. Mice were trained to associate an auditory cue with a potential threat, revealing a crucial connection between two parts of the brain—the ventral hippocampus and basolateral amygdala—in coordinating threat response.
This discovery could provide a foundation for further research on brain connections in more complex social situations and potential therapeutic targets.
- A specific brain circuit enabling rapid, coordinated response to threats in animals has been identified.
- This discovery was made through studying synchronized immobility in pairs of mice, focusing on a connection between the ventral hippocampus and basolateral amygdala.
- The study provides a potential base for advancing research on social communication and developing targeted therapies for neuropsychiatric disorders.
Source: Virginia Tech
Individual fish in schools scatter in unison when a predator is in their midst.
Similar examples of precisely coordinated group movements and immobility during threats have long been observed in insects and mammals.
Now, for the first time, a brain pathway has been discovered that enables individual animals to rapidly coordinate a unified response, with no rehearsal required.
Publishing recently in the print edition of the journal Biological Psychiatry, Virginia Tech scientists with the Fralin Biomedical Research Institute at VTC described how they studied synchronized immobility in pairs of mice and identified the underlying brain circuit responsible for this behavior.
The study provides an identified target to advance research on the poorly understood brain activity that underlies coordinated group movement and, more broadly, social communication in general, which is compromised in a variety of human neuropsychiatric disorders such as attention hyperactivity disorder (ADHD), autism spectrum disorders (ASD) and social communication disorder (SCD).
“Examples of coordinated defensive responses in nature are numerous – oxen, for example, form a circle when they face a threat,” said Alexei Morozov, assistant professor of the Fralin Biomedical Research Institute and corresponding author of the study.
“Synchronization under threat is an evolutionary-conserved survival mechanism and occurs across species, including humans. This type of behavior has never been measured in a lab before, but now we can now quantify this response and explore the underlying mechanisms.”
Mice were trained to associate an auditory cue to a potential threat, like a fire drill. The researchers studied parts of the brain that process and remember fear and social information, and they found that a specific connection between two parts of the brain, the ventral hippocampus and basolateral amygdala, plays an important role in coordinating behavior when faced with a threat.
The information suggests a method to investigate these brain connections in more complicated situations. Although the study began with pairs of individuals, more research is needed to determine whether the same pathway is responsible for coordinating larger group behavior, such as huddling, in larger groups.
“This gives us a way toward a deeper understanding of social behavior,” Morozov said. “At home and at work, people coordinate and exchange information with partners. Now we have a model that helps us understand the underlying brain pathway.”
“This is among the most significant discoveries made in recent years on identifying the sites and the potential underlying mechanisms in the brain that mediate these types of important social interactions,” said Michael Friedlander, Virginia Tech vice president for health sciences and technology and executive director of the Fralin Biomedical Research Institute.
“While the pathologies in these behaviors are well characterized in human clinical populations, attempts at effective therapies have been hampered by a lack of understanding of which brain circuits and biological processes are impacted.
“Dr. Morozov and his team have designed and implemented an elegant series of experiments in mice to provide a potentially powerful base from which to advance this science and hopefully shorten the time to develop more strategically targeted therapies for humans.”
Research assistant professor Wataru Ito and research assistant Alexander Palmer, also of the Fralin Biomedical Research Institute’s Center for Neurobiology Research, participated in the research study.
About this neuroscience research news
Original Research: Closed access.
“Social Synchronization of Conditioned Fear in Mice Requires Ventral Hippocampus Input to the Amygdala” by Alexei Morozov et al. Biological Psychiatry
Social Synchronization of Conditioned Fear in Mice Requires Ventral Hippocampus Input to the Amygdala
Social organisms synchronize behaviors as an evolutionary-conserved means of thriving. Synchronization under threat, in particular, benefits survival and occurs across species, including humans, but the underlying mechanisms remain unknown because of the scarcity of relevant animal models. Here, we developed a rodent paradigm in which mice synchronized a classically conditioned fear response and identified an underlying neuronal circuit.
Male and female mice were trained individually using auditory fear conditioning and then tested 24 hours later as dyads while allowing unrestricted social interaction during exposure to the conditioned stimulus under visible or infrared illumination to eliminate visual cues. The synchronization of the immobility or freezing bouts was quantified by calculating the effect size Cohen’s d for the difference between the actual freezing time overlap and the overlap by chance.
The inactivation of the dorsomedial prefrontal cortex, dorsal hippocampus, or ventral hippocampus was achieved by local infusions of muscimol. The chemogenetic disconnection of the hippocampus-amygdala pathway was performed by expressing hM4D(Gi) in the ventral hippocampal neurons and infusing clozapine N-oxide in the amygdala.
Mice synchronized cued but not contextual fear. It was higher in males than in females and attenuated in the absence of visible light. Inactivation of the ventral but not dorsal hippocampus or dorsomedial prefrontal cortex abolished fear synchronization. Finally, the disconnection of the hippocampus-amygdala pathway diminished fear synchronization.
Mice synchronize expression of conditioned fear relying on the ventral hippocampus-amygdala pathway, suggesting that the hippocampus transmits social information to the amygdala to synchronize threat response.