Parafascicular Thalamic and Orbitofrontal Cortical Inputs to Striatum Represent States for Goal-Directed Action Selection.

Sandy Stayte,Laura A Bradfield,Bryce Vissel,Amolika Dhungana

doi:10.3389/fnbeh.2021.655029

Abstract

Several lines of evidence accrued over the last 5–10 years have converged to suggest that the parafascicular nucleus of the thalamus and the lateral orbitofrontal cortex each represent or contribute to internal state/context representations that guide action selection in partially observable task situations. In rodents, inactivations of each structure have been found to selectively impair performance in paradigms testing goal-directed action selection, but only when that action selection relies on state representations. Electrophysiological evidence has suggested that each structure achieves this function via inputs onto cholinergic interneurons (CINs) in the dorsomedial striatum. Here, we briefly review these studies, then point to anatomical evidence regarding the afferents of each structure and what they suggest about the specific features that each contribute to internal state representations. Finally, we speculate as to whether this role might be achieved interdependently through direct PF→OFC projections, or through the convergence of independent direct orbitofrontal cortex (OFC) and parafascicular nucleus of the thalamus (PF) inputs onto striatal targets.

Highlights

To select the optimal action in many given situations, it has been posited that organisms must mentally represent that situation by integrating features of their internal environment with those of the external environment
To draw upon an example we have given previously (Bradfield and Hart, 2020), if you visit a particular restaurant often, upon visiting you might combine external information about the sights/sounds/smells of the restaurant itself with internal knowledge that it is Saturday and pasta is the daily special, before making an order for pasta. This integrated ‘‘state’’ representation has been claimed to rely on both the parafascicular nucleus of the thalamus (PF) and the orbitofrontal cortex (OFC), when it requires unobservable features to be inferred from memory
When the lateral OFC was lesioned in one hemisphere, cholinergic interneurons (CINs) in the ipsilateral dorsomedial striatum reduced block decoding to chance level. These results suggest that in intact animals, CINs infer some kind of state representation that enables the animal to identify the currently active block, allowing them to make accurate choices and they further suggest that this function is dependent on inputs from lateral OFC

Summary

Frontiers in Behavioral Neuroscience

Several lines of evidence accrued over the last 5–10 years have converged to suggest that the parafascicular nucleus of the thalamus and the lateral orbitofrontal cortex each represent or contribute to internal state/context representations that guide action selection in partially observable task situations. Electrophysiological evidence has suggested that each structure achieves this function via inputs onto cholinergic interneurons (CINs) in the dorsomedial striatum. We briefly review these studies, point to anatomical evidence regarding the afferents of each structure and what they suggest about the specific features that each contribute to internal state representations. We speculate as to whether this role might be achieved interdependently through direct PF→OFC projections, or through the convergence of independent direct orbitofrontal cortex (OFC) and parafascicular nucleus of the thalamus (PF) inputs onto striatal targets

INTRODUCTION

Conclusion and Potential Implications