The Thalamus as a Blackboard for Perception and Planning.

Robert Worden,Victorita Neacsu,Max S Bennett

doi:10.3389/fnbeh.2021.633872

Abstract

It has been suggested that the thalamus acts as a blackboard, on which the computations of different cortical modules are composed, coordinated, and integrated. This article asks what blackboard role the thalamus might play, and whether that role is consistent with the neuroanatomy of the thalamus. It does so in a context of Bayesian belief updating, expressed as a Free Energy Principle. We suggest that the thalamus-as-a-blackboard offers important questions for research in spatial cognition. Several prominent features of the thalamus—including its lack of olfactory relay function, its lack of internal excitatory connections, its regular and conserved shape, its inhibitory interneurons, triadic synapses, and diffuse cortical connectivity—are consistent with a blackboard role.Different thalamic nuclei may play different blackboard roles: (1) the Pulvinar, through its reciprocal connections to posterior cortical regions, coordinates perceptual inference about “what is where” from multi-sense-data. (2) The Mediodorsal (MD) nucleus, through its connections to the prefrontal cortex, and the other thalamic nuclei linked to the motor cortex, uses the same generative model for planning and learning novel spatial movements. (3) The paraventricular nucleus may compute risk-reward trade-offs. We also propose that as any new movement is practiced a few times, cortico-thalamocortical (CTC) links entrain the corresponding cortico-cortical links, through a process akin to supervised learning. Subsequently, the movement becomes a fast unconscious habit, not requiring the MD nucleus or other thalamic nuclei, and bypassing the thalamic bottleneck.

Highlights

The thalamus occupies a central position in the brain
Following the Bayesian brain hypothesis (Knill and Pouget, 2004; Doya, 2007; Rao, 2010)—and its expression via the Free Energy Principle (Friston, 2003)—we propose that in its blackboard role, the thalamus brings about a particular result—the aggregation, or summing, of the free energy contributions from diverse cortical regions, as they join in dynamic coalitions for active perceptual inference and planning
This article has described a promising alignment between two different approaches in the study of the brain: 1. Bayesian inference, as formalized in the Free Energy Principle, as a framework to understand active inference and scene construction as the aggregation of multiple knowledge sources

Summary

INTRODUCTION

The thalamus occupies a central position in the brain. Because of its volume and extensive cortical connections (Sherman and Guillery, 2006) it has significant metabolic costs. One might propose that the MD nucleus of the thalamus (and possibly other thalamic nuclei) uses a shared generative model of peripersonal space, as orchestrated in the pulvinar, to plan, to test in imagination, and to execute, novel or complex movements, with the PFC This interpretation of the role of the MD nucleus is consistent with:. For the risk-reward trade-off, as there are many potential risks, and a few of them are significant at any time, free energies from a dynamic coalition of knowledge sources need to be summed—so hard-wired cortico-cortical connections are less suitable to do the sum, and a central blackboard/aggregator is a more suitable architecture This is consistent with the known role of the paraventricular nucleus in these trade-offs, and a blackboard role for the thalamus. To grasp a piece of fruit, the task has four stages: 1. Arm move: Move the arm so that the hand is in the right place

Eat fruit

CONCLUSION

DATA AVAILABILITY STATEMENT