femme Neuroscience

Some Topics

  • Thalamus

    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 using templates to regulate complex interactions of all brain systems. The templates are based on innate patterns and are modified by learning. Mease wrote:" A major synaptic input to the thalamus originates from neurons in cortical layer 6 (L6); during sensory processing... L6 input to the thalamus can shape both the overall gain and the temporal dynamics of sensory responses that reach the cortex."

    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 attributes of cognition. The intellectual challenge is to become comfortable with complex, self-regulating, recursive systems that do not require an overseer.

    Halassa and Kastner wrote:” “We highlight recent studies across rodents and primates showing how thalamus contributes to attentional control. In addition to high-fidelity information relay to or between cortical regions, thalamic circuits shift and sustain functional interactions within and across cortical areas. This thalamic process enables rapid coordination of spatially segregated cortical computations, thereby constructing task-relevant functional networks. Because such function may be critical for cognitive flexibility, clarifying its mechanisms will likely expand our basic understanding of cognitive control and its perturbation in disease.” (Michael M. Halassa & Sabine Kastner. Thalamic functions in distributed cognitive control. Nature Neuroscience 20, 1669–1679 (2017)

    The “executive system” is a popular construct, a hypothetical entity that integrates different cognitive processes. The identification of real functional components remains difficult. We would like to explain a variety of manifest properties of the brain such as alerting, orienting mechanisms, goal directed behaviors, strategizing, decision making, planning, sequencing, and social interactions. Patients with frontal lobe damage, for example, display variations of the “dysexecutive syndrome.” As with all broad, metaphorical categories the term, executive function, may obstruct, rather than enhance understand of how different brain modules interact to perform different tasks. All attempts to localize executive function are misleading since brains are inherently recursive, self-regulating, integration systems.

    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. They 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. Although thalamocortical synapses are less dense than corticocortical synapses, their effect on cortical activity is important.

    Van der Werf et al stated that the thalamic midline and intralaminar nuclei form an 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.

    The Pulvinar is about 30% of the thalamic mass and has 4 subsections The pulvinar’s main role is creating spatial visual attention. Gatta et al reviewed pulvinar functions: “There are at least two aspects in which the pulvinar seems to be instrumental for selective visual processes. The first aspect concerns pulvinar connectivity pattern. The pulvinar is connected with brain regions known to be playing a role in attentional mechanisms, such as area V4, the superior colliculus (SC), and the inferior parietal cortex (IP). Additionally, the pulvinar is richly interconnected with multiple cortical areas. This enables the pulvinar to serve as a hub for brain communication, potentially gating the flow of information across different regions. The second aspect concerns neuronal circuits intrinsic to the pulvinar. We claim these circuits are subserving three basic steps regarding the allocation of spatial attention: disengaging from the current focus of attention, moving it to a new target, and engaging it at a new position.”
    (Gattaa, R et al. The Role of the Pulvinar in Spatial Visual Attention. Advances in anatomy, embryology, and cell biology. 2018, DOI: 10.1007/978-3-319-70046-5_12, PMID: 29116453)


  • Neuroscience Notes

  • This book 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. Everyone needs to know something about neuroscience. The brain has become a popular topic in all media, but confusions arise when the brain becomes an abstract fantasy in the minds of journalists and product promoters. While it is true that brain is the organ of the mind, our language makes it difficult to speak correctly at different levels of meaning. Neuroscience notes will give the intelligent reader and understanding of how the brain actually works.
  • 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, Intelligence and Learning. Neuroscience notes is available as eBook download from Alpha Online.
  • The author is Stephen Gislason MD

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    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 2018. 306 Pages