This article addresses those questions, relating the blackboard proposals to Bayesian inference in the brain, as entailed by the Free Energy Principle ( Friston, 2003). Blackboard functions appear sufficiently important to justify having the thalamus but what exactly do they mean? What does a blackboard do? Is the neuroanatomy and neurophysiology of the thalamus consistent with a blackboard function? It has been proposed ( Baars, 1988 Mumford, 1991 O’Reilly et al., 2017, 2020 Dehghani and Wimmer, 2018) that the thalamus acts as a blackboard or global workspace in the brain. These are not the only theories of thalamic function. Compared to its cost and central position, many theories of thalamic function have an unsatisfactory aspect if the thalamus is merely a relay for sense data, or merely an enforcer of cortical rhythms, or a controller of arousal, why devote all that expensive brain real estate to such simple functions, which could perhaps be done more locally in cortex or brainstem? These thalamic functions do not seem to license the significant cost of the thalamus. Because of its volume and extensive cortical connections ( Sherman and Guillery, 2006) it has significant metabolic costs. The thalamus occupies a central position in the brain. Subsequently, the movement becomes a fast unconscious habit, not requiring the MD nucleus or other thalamic nuclei, and bypassing the thalamic bottleneck. 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. (3) The paraventricular nucleus may compute risk-reward trade-offs. (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. 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. We suggest that the thalamus-as-a-blackboard offers important questions for research in spatial cognition. It does so in a context of Bayesian belief updating, expressed as a Free Energy Principle. This article asks what blackboard role the thalamus might play, and whether that role is consistent with the neuroanatomy of the thalamus. It has been suggested that the thalamus acts as a blackboard, on which the computations of different cortical modules are composed, coordinated, and integrated. 2Independent Researcher, New York, NY, United States.1Wellcome Centre for Human Neuroimaging, Institute of Neurology, University College London, London, United Kingdom.
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