A causal role for pulvinar in coordinating task independent cortico-cortical interactions

Pulvinar is the largest nucleus in the primate thalamus and has topographically organized connections with multiple cortical areas, thereby forming extensive cortico-pulvino-cortical input-output loops. Neurophysiological studies have provided evidence for a role of these transthalamic pathways in regulating information transmission between cortical areas. However, a causal role of pulvinar in regulating cortico-cortical interactions has not yet been demonstrated. In particular, it is not known whether pulvinar’s influences on cortical networks are task-dependent or reflect more basic large-scale network properties that maintain functional connectivity across a network regardless of active task demands. In the current study, under a passive viewing condition, we conducted simultaneous electrophysiological recordings from interconnected ventral (area V4) and dorsal (LIP) nodes of the macaque visual system while reversibly inactivating the dorsal part of lateral pulvinar (dPL), which shares common anatomical connectivity with V4 and LIP. Our goal was to probe a causal role of pulvinar in regulating cortico-cortical interactions in the absence of any active task demands. Our results show a significant reduction in local field potential phase coherence between LIP and V4 in low frequencies (4-15 Hz) following muscimol -a potent GABA A agonist -injection into dPL. At the local level, no significant changes in firing rates or LFP power were observed in LIP or in V4 following dPL inactivation. These results indicate a causal role for pulvinar in synchronizing neural activity between interconnected cortical nodes of a large-scale network, even in the absence of an active task state. Significance Statement Pulvinar, the largest nucleus of the primate thalamus, has been implicated in several cognitive functions. The extensive cortico-pulvino-cortical loops formed by pulvinar are suggested to be regulating information transmission between interconnected cortical areas. However, a causal evidence for pulvinar’s role in cortico-cortical interactions in the absence of active task demands is not yet clear. We conducted simultaneous recordings from nodes of macaque visual system (areas V4 and LIP) while inactivating the dorsal part of the lateral pulvinar (dPL) under a passive viewing condition. Our results show a significant reduction in local field phase coherence between LIP and V4 in low frequencies (4-15 Hz) following inactivation of dPL, thus providing evidence for a causal role of pulvinar in regulating cortico-cortical interactions even in the absence of an active task state.