The corpus striata (basal ganglia) complex:
An essential component of MacLean's protoreptilian brain and often referred to as the basal ganglia, the corpus striata "are most closely linked with the initiation, smoothness, and precision of movement," writes Restak in Brainscapes, "and are responsible for the automatic movements we make without thinking."
Regarding the older terminology, the term basal generally means situated at or forming a base. Ganglion is the singular of ganglia and means "a mass of nerve tissue containing cell bodies of neurons that are located outside the central nervous system," according to MedlinePlus Dictionary. So the term ganglia is a misnomer. Nuclei would be more accurate since the structures are in the brain, the primary component of the central nervous system. The basal nuclei then are a collection of interconnected brain structures deep within the brain. However, more specific terms, such as corpus striatum, seem to be increasingly employed so the structures will discussed using the more precise terminology.
The anatomical meaning of the term corpus is any mass of tissue in the body that has a distinct structure or function. As you can see in the illustration to the right (image links to source), the corpus striatum, which includes the structures labeled caudate nucleus, lentiform nucleus, and putamen, is indeed an oddly shaped and distinct structure. The corpus striatum's function, as we will discuss, is certainly distinct. The nuclei that make up each corpus striatum are located, as mirror image masses, in each hemisphere to the outside of the more centrally located thalami. Referenced in the plural, these structures are called the corpus striata. Components of the corpus striatum, the caudate nucleus and the lentiform nucleus are, according to MedlinePlus Dictionary, "separated by sheets of white matter to give the mass a striated appearance" when dissected into sections. Thus, the name corpus striatum.
The term caudate is derived from caudal, which in this case means "of, relating to, or being a tail." The term lentiform is taken from lenticular, which MedlinePlus Dictionary defines as "having the shape of a double-convex lens." Nestled within the curve of each lentiform nucleus is a pale yellow globular mass constituting the globus pallidus, also called the pallidum. These structures are colored bright red in the illustration to the left (image links to source).
In the brains of persons afflicted with Huntington's Disease, which has a genetic etiology, "excessive levels of endogenous glutamate may gradually destroy the basal ganglia [corpus striata]," writes Panksepp in Affective Neuroscience. "Although these patients eventually exhibit severe motor disabilities, their mental status is initially compromised by a schizoid type of disorder characterized by disjointed cognitive activity. For instance, a person may remember all the steps in a favorite recipe but not be able to sequence them into a final product. Apparently, the flow of information through striatal-thalamic-cortical loops helps solidify behavior sequences based on various component parts. The cortex contains the component parts, but the striatum welds them into a coherent plan."
John A. Beal, Department of Cellular Biology and Anatomy, Louisiana State University Health Sciences Center, provides the following two images of anatomical specimens (link to source). In the first picture below right, the right brain hemisphere has been removed. You can see the left hemisphere head of the caudate nucleus, labeled 1, and part of the caudal, tail-like portion of the nucleus, labeled 2. The lentiform nucleus is hidden behind the thalamus, labeled 5, and the interthalamic adhesion, labeled 6.
Additional structures work with the corpus striata to manage movement. The subthalamic nucleus interconnects with the globus pallidus, which remember is nestled within the curve of the lentiform nucleus. Also, the substantia nigra, a group of cells named for their dark color, located in the midbrain, connect with the corpus striata by way of axonal fibers called the nigrostriatal pathway. The substantia nigra is, according to MedlinePlus Dictionary, "a layer of deeply pigmented gray matter situated in the midbrain and containing the cell bodies of a tract of dopamine-producing nerve cells whose secretion tends to be deficient in Parkinson's disease." You can see the substantia nigra clearly in the image below.
It is to be noted here that in addition to the striated nuclei, associated structures including the globus pallidus, nucleus accumbens, entopeduncular nucleus, ventral tegmental area (VTA), and substantia nigra are all considered part of a system that manages movement. (You can see the approximate location of the VTA in the image above.) Grouped together, these structures are sometimes referred to as the striatal complex. Given that not all of the structures included in this complex have a striated appearance, It is preferred not to use the adjective "striatal," so this complex is called the corpus striata complex. Regarding this system, Panksepp writes: "Both cognitive and emotional information converges here before coherent behavior can occur." Later, he explains that "it seems likely that basal ganglia [corpus striata] circuitry elaborates a primitive feeling of motor presence, which may represent a primal source of 'willpower.' The more highly evolved brain regions must still utilize this system as a final output pathway for behavior."
Neural feedback networks connect the corpus striata to the surrounding neocortex, with primary connections to the cerebral motor areas. To enable finely controlled, smooth movements, neural networks within the corpus striata rapidly manage the interplay of both excitatory and inhibitory signals, integrating input from the environment with information related to body position. Imagine you're at an elegant dinner party, lifting to your lips a fine china cup filled to the brim with coffee into which you've poured too much cream. Not too fast! Certainly you feel the inhibitory signals, the micro-movements necessary to raise the cup without spilling a drop, especially after having two glasses of wine with dinner. The balance of excitatory and inhibitory signals necessary to execute smooth movements depends on neurotransmitters, including dopamine. This explains why Parkinson's disease—marked by a slow, rigid, shuffling gait—develops when dopamine supply from the substantia nigra to the corpus striata is deficient. Corpus striata networks are also responsible for managing memorized movement—those we undertake without forethought. Thus, an excess of dopamine in these networks may help explain the unwanted repetitive, stereotyped movements seen in OCD and Tourette syndrome.
the corpus striata was first learned from Thomas Aird's article titled "Functional Anatomy of the Basal Ganglia," which appeared in the October 2000 issue of Journal of Neuroscience Nursing. Aird explains that some of the more common OCD symptoms are indicative of an organic brain disorder, rather than a psychological disorder. He writes: "Unlike Parkinson's disease, which has historically been seen as an organic brain disorder, movement disorders (dyskinesias) often play out in normal human routines—such as hand washing, counting, or sorting. Thus, people with such symptoms have often been incorrectly construed as having a 'psychological' disorder."
We will discuss dopamine functioning in the corpus striata complex and this system's role in generating symptoms in more detail in Parts 2 and 3 of CorticalBrain.com. To give you some indication of the importance of the corpus striata complex in generating normal versus dysfunctional behavior, it will be mentioned here that Graybiel and Rauch reports, in "Toward a Neurobiology of Obsessive-Compulsive Disorder" (2000), that lesions in the corpus striata and/or the globus pallidus can produce "striking OCD-like behavior."
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