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The Brain's Cerebral Cortex (Neocortex)

Human Brain's Five Lobes

The brain's five lobes:

Human Skull Bones

Wikipedia's entry for the "Human brain" states: "the lobes are named after the bones of the skull that overlie them. There is one exception: the border between the frontal and parietal lobes is shifted backward to the central sulcus, a deep fold that marks the line where primary somatosensory cortex and primary motor cortex come together."

The lobe designations are sometimes used to indicate the relative position of structures. For example, the amygdalae are nestled within the temporal lobes. While we will discuss specialized areas of the neocortex later in this narrative, we will discuss the lobes in brief below. It is important to remember that a lobe does not function independently. Lobe designations are merely an anatomical reference. Damasio is again quoted to forestall the impulse to credit this or that lobe with a discrete process. He points out that "within one second in the life of our minds, the brain produces millions of firing patterns over a large variety of circuits distributed over various brain regions."

The frontal lobe is involved in establishing priorities and planning. Richard M. Restak, in Brainscapes: An Introduction to What Neuroscience Has Learned about the Structure, Function, and Abilities of the Brain (1995), writes: "The frontal lobe makes up 50 percent of the volume of each cerebral hemisphere in humans. It initiates all motor activity, including speech; its most anterior divisions, the prefrontal lobes and supplementary motor cortex, integrate personality with emotion and transform thought into action."

The temporal lobe contains a sensory area related to hearing. Nestled within each temporal lobe are the amygdala and the hippocampus, which are, writes Restak in Brainscapes, "involved in learning, memory and the experience and expression of emotion." A portion of the temporal lobe, called the entorhinal cortex, channels cortical inputs to the hippocampus. Restak writes: "Fibers from all four lobes, along with association fibers uniting these separate connections into one unified experience, converge into the hippocampal region." In Evolving Brains, Allman points out that the amygdala—so important to emotional processing—also receives input from a cortical area within the temporal lobe called the inferotemporal visual cortex, which is "greatly expanded in higher primates." Allman notes that "Charles Goss, Robert Desimone, Edmund Rolls, and David Perrett and their colleagues have shown that neurons in part of the inferotemporal cortex are especially sensitive to the images of faces." We will discuss specific areas of the cortex involved in processing different kinds of visual stimuli later in this narrative.

The occipital lobe includes sophisticated topographical maps with complex interconnections required for visual processing, and according to MedlinePlus Dictionary, has "the form of a 3-sided pyramid." The Merck Manuals Online Medical Library states that in addition to processing and interpreting vision, cortical areas in the occipital lobe enable people to form visual memories and integrate visual perceptions with spatial information coming from the adjacent parietal lobes. If a head injury or stroke damages the occipital lobes, visual agnosia sometimes develops. In an entry for brain dysfunction, the Merck Manual home edition defines agnosia as the "loss of the ability to associate objects with their usual role or function." With sufficient damage to the occipital lobe, "People cannot recognize familiar faces or common objects, such as a spoon or a pencil, even though they can see these things."

The parietal lobe contains an area that processes bodily sensations—the somatosensory cortex, which we will discuss further later in this narrative. In Brainscapes, Restak writes: "The parietal lobe is the receiving station for sensory information from the opposite side of the body and is responsible for the integration of what is seen with what is felt via a network of association fibers.

Brain's Sylvian Fissure

A fifth lobe, the insula, is located "in the center of the cerebral hemisphere that is situated deeply between the lips of the sylvian fissure," according to MedlinePlus Dictionary. To get an idea of where the insula is located, the image to the right (links to source) illustrates the location of the sylvian fissure. This image is from web pages authored by Jody Culhan, University of Western Ontario; the web page is titled "fMRI for Newbies." The insula, hidden inside the sylvian fissure, is sometimes called the central lobe or island of Reil. The insula "integrates sensory and autonomic information from the viscera," according to Merck Manuals Online Medical Library. This lobe plays a role in certain language functions and when damaged can lead to aphasia, the inability to use or understand spoken and written language. According to the Merck Manuals, the insula also "processes aspects of pain and temperature sensation and possibly taste."

Next-> The Brain Cerebral Cortex Neocortex - The brain's frontal lobes

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