The role of the parafascicular thalamic nucleus in action initiation and steering

The parafascicular (Pf) nucleus of the thalamus has been implicated in arousal and attention, but its contributions to behavior remain poorly characterized. Here, using in vivo and in vitro electrophysiology, optogenetics, and 3D motion capture, we studied the role of the Pf nucleus in behavior using a continuous reward tracking task in freely moving mice. We found that many Pf neurons precisely represent vector components of velocity, with a strong preference for ipsiversive movements. Their activity usually leads velocity, suggesting that Pf output is critical for self-initiated orienting behavior. To test this hypothesis, we expressed excitatory or inhibitory opsins in VGlut2+ Pf neurons to manipulate neural activity bidirectionally. We found that selective optogenetic stimulation of these neurons consistently produced ipsiversive head turning, whereas inhibition stopped turning and produced downward movements. Taken together, our results suggest that the Pf nucleus can send continuous top-down commands that specify detailed action parameters (e.g., direction and speed of the head), thus providing guidance for orienting and steering during behavior.

Automated summary

By using a continuous reward tracking task in freely moving mice and employing various techniques such as electrophysiology, optogenetics, and 3D motion capture, this study examined the role of the parafascicular (Pf) nucleus of the thalamus in behavior. The findings suggest that Pf neurons accurately represent velocity components and show a preference for same-side movements. The activity of Pf nucleus is crucial for self-initiated orienting behavior, as its output can specify detailed action parameters and provide guidance for orienting and steering during behavior.