SOCIAL TOUCH SUPPRESSES AGGRESSION VIA THALAMIC MECHANISMS

Aggression is a fundamental social behavior, but its excessive escalation is maladaptive and therefore requires neural mechanisms for suppression. Here, we investigated whether the posterior intralaminar thalamic nucleus (PIL) limits aggressive behavior by integrating social tactile signals.
Rodents were housed under three conditions: complete isolation, barrier housing without tactile contact, and pair housing. Both isolated animals and those deprived of tactile interaction exhibited significantly elevated aggression compared to controls, indicating that social touch restrains aggressive behavior. Using fiber photometry, we found that PIL neuronal activity increased immediately upon social tactile contact and subsequently declined. To test causality, we manipulated socially activated PIL neurons using chemogenetics (vGATE system with DREADDs) during the resident–intruder test. Activation of these neurons markedly reduced aggression, whereas their inhibition enhanced it. Consistently, optogenetic stimulation of PIL neurons decreased the duration of individual attacks.
Circuit-level analyses revealed that selective activation of the PIL–medial preoptic area (MPOA) pathway significantly suppressed aggression, while inhibition of this projection produced the opposite effect. In contrast, chemogenetic stimulation of the ventromedial hypothalamic nucleus (VMH)–to–PIL pathway increased aggressive behavior, indicating that VMH input can override PIL-mediated suppression.
Together, these findings demonstrate that PIL neurons encode social tactile information and, via projections to the MPOA, act to restrain and terminate aggressive behavior. Conversely, excitatory input from the VMH to the PIL can promote aggression when necessary. The PIL thus emerges as a key relay integrating tactile social cues to dynamically regulate the expression of aggression.