The parafascicular nucleus of the thalamus orchestrates coordinated skeletomotor, autonomic, and aversive state transitions

The parafascicular nucleus (Pf), part of the intralaminar thalamic nuclei, has been implicated in diverse functions such as attention, nociception, and behavioral flexibility, yet its precise contributions to behavior remain poorly defined. In this study, we used optogenetics in male and female mice to study the role of Pf projection neurons using high-resolution and continuous measures to quantify both skeletomotor and autonomic behavioral outputs as well as motivational valence. We showed that selective Pf stimulation resulted in wide-ranging effects, including ipsiversive turning, facial and whisker movements, pupil constriction, and heart rate reduction. Finally, we found that Pf stimulation could be highly aversive, as mice showed strong place aversion to areas where stimulation was delivered. Together our results indicate that Pf outputs can ultimately influence both skeletomotor outputs like turning and autonomic outputs like pupil constriction. The latter parasympathetic responses may be directly related to the role of the Pf in regulating motivational and emotional valence. These findings broaden our understanding of Pf function and suggest it may serve as a major hub for the integration of behavioral state feedback and top-down command of a variety of effectors. Significance statementThis study demonstrates that the parafascicular nucleus (Pf) of the thalamus plays a critical role in coordinating both skeletomotor and autonomic responses, as evidenced by optogenetic stimulation in mice triggering rapid ipsilateral turning, facial movements, pupil constriction, and heart rate reduction. The findings reveal that Pf activation induces an aversive state, highlighting its involvement in motivational valence. These insights expand our understanding of Pfs top-down regulatory influence on behavior.