On the left, the standard situation where somatostatin-expressing interneurons (SST+, blue) in the anterior cingulate cortex (ACC) are able to control the degree of observational fear in mice. SST+ decrease the excitability of the neighboring neurons (pyramidal cells, brown) via the release of the inhibitory neurotransmitter GABA (purple circles). On the right, the neurophysiological mechanism in SST+ neuron-specific Nrxn3 knockout (KO) mice or with SST+ neurons in the ACC optogenetically inhibited. The NRXN3 protein is absent and SST+ neurons release less GABA in the ACC. As a result, dysfunctional inhibitory circuits in the ACC caused hyperactivity of pyramidal neurons, resulting in elevated empathic fear, which is similar to the 129S1 mice.