When they optogenetically inhibited the ACC-BLA circuits only in the right brain, mice showed reduced observational freezing.
As a result, they found that brain rhythms with the range of 5-7 Hz selectively increased in the ACC and BLA at the specific moment within the observer mice at the time they showed empathic freezing behavior.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 the brain waves using EEG (Figure 2B).Through the closed-loop experiment, they could selectively disrupt 5-7 Hz rhythms in the ACC-BLA circuit, which in turn resulted in significant impairment of observational fear induced freezing during the 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 (4-12 Hz) rhythms may tune the synchronized activities within the ACC-BLA circuit.This study strongly indicates that hippocampal-dependent 5-7 Hz synchronized oscillations in the ACC-BLA specifically drive empathic responses in mice.
Hee-Sup Shin remarked, “Considering the universality of observational fear across mammals, it is reasonable to suppose a similar neural signature critical for affective empathy may be found in humans and could be used to identify empathy dysfunction in humans with psychiatric disorders involving severe social deficits.”.
“Hemispherically lateralized rhythmic oscillations in the cingulate-amygdala circuit drive affective empathy in mice” by SHIN Hee-Sup et alHemispherically lateralized rhythmic oscillations in the cingulate-amygdala circuit drive affective empathy in miceHere, we show that reciprocal projections between the anterior cingulate cortex (ACC) and basolateral amygdala (BLA) in the right hemisphere are essential for observational fear, and 5–7 Hz neural oscillations were selectively increased in those areas at the onset of observational freezingA closed-loop disruption demonstrated the causal relationship between 5–7 Hz oscillations in the cingulo-amygdala circuit and observational fear responsesTogether, these results indicate that hippocampus-dependent 5–7 Hz oscillations in the cingulo-amygdala circuit in the right hemisphere are the essential component of the cognitive process that drives empathic fear, but not freezing, in general