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The Brain's Cerebral Cortex (Neocortex)

In Evolving Brains (2000), John Allman explains that cortex means "the outer shell or rind of an object." He explains that the prefix "neo" implies that it is new.





The brain's neocortex:

Brain's Cerebral Cortex

Allman writes: "The neocortex is found only in mammals, although it is related to forebrain structures found in other vertebrate classes. The neocortex has expanded enormously in the brains of humans and other advanced mammals." Robert M. Sapolsky, in his video course, Biology and Human Behavior: The Neurological Origins of Individuality, 2nd edition, refers to the neocortex as a "primate specialization," terminology which corresponds to Allman's description of an expanded neocortex in "advanced mammals." In the image to the right (image links to source), you can see the medial longitudinal fissure separating the left and right hemispheres of the human neocortex. This image is from BrainMaps.org; the project investigator for this project is Edward G. Jones and other scientists from the Center for Neuroscience, University of California, Davis and University of Wisconsin, Madison.

Regarding the neocortex, Allman writes:

The neocortex, the sheetlike, six-layered structure in the roof of the forebrain that is found in all mammals and only in mammals, was probably present in the earliest true mammals; it is possible that it may actually have evolved earlier, at some point after the separation of the line leading to the mammals from the lines leading to reptiles and birds. The antecedents of the neocortex are present in the telencephalic roof in even the most primitive vertebrates. The neocortex is a specialization in the telencephalon that parallels the formation of the dorsal ventricular ridge and wulst in reptiles and birds. The neocortex is just as much a unique defining feature of mammals as are the mammary glands or the malleus and incus in the middle ear. As with the other distinctive features of mammals, the neocortex probably evolved as a part of a set of adaptations related to temperature homeostasis. The large increases in metabolic expenditure necessary to sustain temperature homeostasis required commensurate increases in the acquisition of food by the early mammals. Since these animals were small and had only a limited capacity to store energy as fat, they were constantly under the threat of starvation. The neocortex stores information about the structure of the environment so that the mammal can readily find food and other resources necessary for its survival (emphasis added).

The anterior cingulate cortex–emotion, attention, and working memory:

Jaak Panksepp, in Affective Neuroscience: The Foundations of Human and Animal Emotions (1998), explains that "the modular unit of the neocortex is a column, a vertically oriented functional grouping of about 4,000 interconnected neurons with comparatively weak connections to immediately neighboring modules. These columns are strongly linked to other cortical modules and to lower brain areas by descending and looping connections. Coherently operating groups of neurons are called functional 'networks' or 'cell assemblies.' An especially important point to remember is that even though the human brain has much more neocortex than other animals of comparable size, this is achieved by the addition of more columnar modules and their interconnections rather than by increasing the quality (i.e., complexity) of cortical columns."

The anterior cingulate cortex–emotion, attention, and working memory:

Brain's Anterior Cingulate Cortex

Before the anatomical differentiations referred to as lobes are discussed , it is better to discuss a most important recessed area of cortex that traditionally has been considered as part of the limbic system or paleomammalian brain. Avoiding specifying specific components of what has in the past been called the limbic system since a discrete system does not exist. the point to remember is that the anterior cingulate cortex is more ancient, from an evolutionary perspective, than outer areas of cortex.

The cingulate cortex shapes itself to the outside curve of the corpus callosum, the thick band of nerve fibers that connects the brain's left and right hemispheres (see The Brain's Two Hemispheres). The term cingulate comes from cingulum, Latin for belt or girdle. This area is sometimes called the cingulate gyrus. The word gyrus means generally circle. Anatomists call each cortical fold a sulcus and the smooth protruding area between folds a gyrus. You can see in the photograph above (image links to source) that the cingulate cortex (all areas labeled 7) is "girdled" or "belted" around the corpus callosum. MedlinePlus Dictionary defines anterior as "relating to or situated near or toward the head… ." Thus, the anterior cingulate cortex in the image above, outlined in red, bumps up against the inside of our frontal lobe. The above image is from John A. Beal, Department of Cellular Biology and Anatomy, Louisiana State University.

In Descartes' Error: Emotion, Reason, and the Human Brain (1994), Antonio R. Damasio writes: "I would like to propose that there is a particular region in the human brain where the systems concerned with emotion/feeling, attention, and working memory interact so intimately that they constitute the source for the energy of both external action (movement) and internal action (thought animation, reasoning). This fountainhead region is the anterior cingulate cortex, another piece of the limbic system puzzle." Damasio goes on to say: "My idea about this region comes from observing a group of patients with damage in and around it. Their condition is described best as suspended animation, mental and external—the extreme variety of an impairment of reasoning and emotional expression."

Damasio calls attention to an interesting phenomenon that illustrates the function of the anterior cingulate cortex. Damage to the motor cortex will affect a voluntary smile but not a genuine, emotional smile generated from within the anterior cingulate cortex. "When a stroke destroys the motor cortex on the brain's left hemisphere and, as a result, the patient has paralysis on the right side of the face," Damasio notes, "the muscles cannot act and the mouth tends to be pulled toward the normally moving side. Asking the patient to open the mouth and reveal the teeth only heightens the asymmetry. Yet when the patient smiles or laughs spontaneously, in response to a humorous remark, something entirely different happens: the smile is normal, both sides of the face move as they should, and the expression is natural, no different from the usual pre-paralysis smile of that individual. This illustrates that the motor control for an emotion-related movement sequence is not in the same location as the control for a voluntary act. The emotion-related movement is triggered elsewhere in the brain, even if the arena for the movement, the face and its musculature, is the same."

To clarify where emotional expression does originate, Damasio writes: "If you study a patient in whom a stroke has damaged the anterior cingulate in the left hemisphere you will see precisely the opposite result. In repose or in emotion-related movement, the face is asymmetrical, less mobile on the right than on the left. But if the patient tries to contract the facial muscles willfully, the movements are carried out normally and symmetry returns. Emotion-related movement, then, is controlled from the anterior cingulate region, from other limbic cortices (in the medial temporal lobe), and from basal ganglia, regions whose damage or dysfunction yields a so-called reverse or emotional facial paralysis."

Paul MacLean made a very interesting observation relating to the cingulate cortex and the bond between mother and child in an article included in the book The Limbic System and Clinical Disorders (B.K. Doane, and K.E. Livingston, eds., Raven Press, New York). MacLean wrote: "It is beginning to appear on the basis of comparative neurobehavioral studies that the cingulate subdivision of the limbic system is implicated in three forms of behavior that characterize the evolutionary transition from reptiles to mammals—namely (a) nursing, in conjunction with maternal care; (b) audiovocal communication for maintaining maternal-offspring contact; and (c) playful behavior. Significantly, the cingulate gyrus and its subcortical connections appear to have no recognizable counterpart in the reptilian brain."

The anterior cingulate cortex may play an important role in bonds between parent and child, as well as other attachments. We explore this idea in Part 2 of CorticalBrain.com, in Chronic stress and frustration related to attachment—implications for depression and OCD. If you jump ahead to this link, remember to click the BACK button on your browser to return here.


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