The thalamus is a cluster of nuclei that contain dense populations of neurons and dense interconnections with every other part of the brain. There are two thalami, lying deep inside each cerebral hemisphere. I compare the thalamus to a multi-channel mixer that combines activity from many brain modules using function-specific templates. The templates are based on innate patterns and are modified by learning.

Consciousness is a monitor image that samples brain activities. In my discussion of consciousness, I suggested that these monitor images and sensations depend on the recursive interaction of the thalamus and cortex. Other modulating information is fed into the mix from the smaller nuclei surrounding the thalamus contributing feelings, mood and other information. 

Because the thalamus is so complexly and recursively connected with all other parts of the brain, focusing on the thalamus to explain executive functions will be misleading to some extent. The interaction of frontal lobe and thalamic circuits is essential, for example, to anticipatory planning - one of the more recent and complex attributes of cognition. The intellectual challenge is to become comfortable with complex, self-regulating, recursive systems that do not require an overseer.

In their review of 10 years of studying the connections of thalamic nuclei in rats, Van der Werf et al stated that the thalamic midline and intralaminar nuclei form awareness, arousing system, involved in cognitive, sensory and motor functions. They proposed that the thalamic nuclei as a whole play a role in awareness, with each of the groups subserving a role in different aspects of awareness:

(1) a dorsal group is involved in viscero-limbic functions

(2) a lateral group is involved in cognitive functions

(3) a ventral group is involved with multimodal sensory processing

(4) a posterior group is involved in limbic functions.

Vertes et al   studied the connections between frontal lobes and the thalamus in rats and suggested that the medial prefrontal cortex is involved in high-order cognitive processes such as decision-making, goal directed behavior, and working memory.  They showed the infralimbic, prelimbic, anterior cingulate cortices connect to midline/medial structures of the thalamus; the medial agranular cortex connects to the intralaminar nuclei, the ventromedial, and ventrolateral nuclei of thalamus; all four divisions of the medial prefrontal cortex project densely to the nucleus reuniens of the thalamus.

The nucleus reuniens is the major source of thalamic input to the hippocampal formation, transferring information from the medial prefrontal cortex to the hippocampus. Their evidence suggests that thalamic nuclei act as mixers and executive controllers of diverse subcortical and cortical structures in the brain.

Neuroscience Notes places the human brain at the center of the universe. Since the brain is the organ of the mind, consciousness and all knowledge is contained within the brain. Neuroscience Notes is part of the Persona Digital Psychology and Philosophy Series of related books. The closely related volumes are the Human Brain, Language and Thinking, Emotions and Feelings, and Intelligence and Learning.

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Neuroscience Notes is published by Persona Digital Books. Copyright 2011, 2012. All rights to reproduction by any means are reserved. We encourage readers to quote and paraphrase topics from Neuroscience Notes published online and expect proper citations to accompany all derivative writings.  The author is Stephen Gislason MD. The latest date of publication is 2012.  The URL to the book description is http://www.personadigital.net/Persona/Neuroscience/  Persona Digital Online is a download server for digital media.  Also See Persona Digital Music Studio