The thalamus and OCD:
In The Tangled Wing: Biological Restraints on the Human Spirit (1982), Melvin Konner calls the thalamus "the major way station of incoming sensation." In What Makes You Tick?, Czerner explains that the thalamus "is the gateway for virtually all of your sensations and directs impulses generated by each of your sensory neurons to its appropriate area in the cortex." For example, the thalamus directs visual information to the primary visual cortex, which we will discuss later in this narrative.
In the photograph to the left (image links to source), you can see that the thalami occupy a central location among the subcortical nuclei. As previously noted, the thalami are actually two mirror-image ovoid masses that occupy each lateral wall of the third ventricle. This image is from John A. Beal of the Louisiana State University.
The thalami are of primary importance in relaying messages from subcortical nuclei to the neocortex. The thalami are integral to what we will call cortical-subcortical circuits, which we will discuss at length in Part 3 of CorticalBrain.com. These circuits possibly shift, in certain situations, into what is called autonomous processing mode whereby one circuit supports cognitive processing while another separate circuit supports more automatic processing and behavior, what we would call compulsions. Building on information in Parts 1 and 2, we extensively discuss the neurocircuitry of obsessions and compulsions in Part 3 of CorticalBrain.com.
The hypothalamus and seeking behavior:
Note in the MRI image below right (image links to source) the small size of the hypothalamus when compared to the size of the thalamus in the image below left (image links to source). In Brainscapes, regarding the hypothalamus, Restak explains that "… despite its diminutive size it is responsible for regulating such critical functions as body temperature, hunger, sexuality, and via connections with the nearby pituitary gland (the 'master gland of the body'), the endocrine system and the composition of the blood and fluid compartments, that internal symphony of circulating chemicals in our bodies aptly described by French physiologist Claude Bernard as the 'internal milieu.'"
The on-line MedlinePlus Dictionary defines the hypothalamus as "a basal part of the diencephalon that lies beneath the thalamus on each side, forms the floor of the third ventricle, and includes vital autonomic regulatory centers (as for the control of food intake)." If you remember the previous discussion on neural tube development, the "diencephalon" develops from the forebrain portion of the neural tube. Also, in our discussion of the autonomic nervous system, we examine the critical role of the hypothalamus in governing sympathetic nervous system reactions including fear, flight, fight, and sexual reactions.
In Descartes' Error, Damasio writes, "The innate neural patterns that seem most critical for survival are maintained in circuits of the brain stem and hypothalamus. The latter is a key player in the regulation of the endocrine glands—among them the pituitary, the thyroid, the adrenals, and the reproductive organs, all of which produce hormones—and in the function of the immune system." Damasio adds, "In turn, the hypothalamus and interrelated structures are regulated not only by neural and chemical signals from other brain regions, but also by chemical signals arising in various body systems."
The illustration to the right (links to source) depicts the major components of the endocrine system. In What Makes You Tick?, Czerner very eloquently writes: "Deep within your brain but well above the brain stem, neurons in your pituitary and hypothalamus evolved from cells that enabled your chordate ancestors to sense the chemical perfume of an unseen mate in a distant meadow and initiate a courtship. Now the sense and regulate the hormones in your blood. They lie deep in the subcortical, central region of the brain, which could be called the seat of your animal soul. This area, truly the heart of your brain, includes several important nuclei that produce and regulate your degree of arousal, the tone and depth of your feelings, and your emotionally directed behavior. The behavior produced in this middle portion of the brain is often labeled instinctual and unthinking because it is less easily modified than the more deliberately planned, finely turned responses generated in the newly acquired cerebral cortex above it."
It is to be noted here that the words Czerner uses to describe the behavior arising from activity in the subcortical nuclei—"less easily modified" and "instinctual and unthinking"—are particularly appropriate when referring to obsessions and compulsions. We discuss the role of subcortical nuclei in producing OCD symptoms in Part 2 and then, more extensively, in Part 3 of CorticalBrain.com.
Grandin and Johnson, in Animals in Translation, elaborate on one of the ideas Jaak Panksepp develops in Affective Neuroscience. Grandin and Johnson write: "Animals and humans share a powerful and primal urge to seek out what they need in life. We depend on this emotion to stay alive, because curiosity and active interest in the environment help animals and people find good things, like food, shelter, and a mate, and it helps us stay away from bad things, like predators." Grandin and Johnson point out that the hypothalamus regulates sex hormones and appetite, which or course leads to the seeking of food and mates. So the authors see the hypothalamus as integral to what Jaak Panksepp, in Affective Neuroscience, calls the SEEKING system. We will discuss the SEEKING system and the neurotransmitter that powers this system, dopamine, in greater detail in Part 2 of CorticalBrain.com
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