Post-weaning social isolation impairs the orbitofrontal cortical circuit subserving contagious pain and prosocial behaviors

Empathic behaviors are sensitive to environmental factors like post-weaning social isolation (SI), yet the mechanisms by which SI affects empathy remain unclear. Here, we show that mice subjected to SI exhibit marked impairments in contagious pain and prosocial behaviors, including allo-grooming and allo-licking toward cagemates experiencing inflammatory pain. Mechanistically, we identify the glutamatergic projection from the ventromedial thalamic nucleus (VM) to the orbitofrontal cortex (OFC) as critical for these empathy-like responses. SI induces hypoexcitability of OFC glutamatergic neurons and attenuates excitatory synaptic transmission within the VM[->]OFC pathway. Remarkably, chemogenetic activation of OFC neurons or the VM[->]OFC projection restores empathic behaviors in SI mice. Furthermore, we uncover a molecular basis for SI-induced OFC hypoexcitability: the downregulation of Grik3, encoding a kainate-type glutamate receptor subunit. These findings reveal a previously uncharacterized thalamocortical mechanism through which early-life social deprivation disrupts empathic behaviors, offering insights into the underpinnings of social-affective dysfunction.