There is a clear advantage to such cortical folding. Having a thinner, folded cortex means information transfer from one point in the brain to another covers less distance and can happen far more rapidly. Researchers knew that gyri and sulci arise in humans during the third trimester of gestation but could never pinpoint the forces behind their formation.
For a long time two explanations held sway but both were riddled with exceptions, according to neuroscientist and co-author Suzana Herculano-Houzel of the Federal University of Rio de Janeiro. The first hypothesis held that the larger a brain is, the more folded its cortex will be. But the idea failed to account for major outliers like the manatee. Cetaceans also proved a problem; their cortices were more convoluted than would make sense for the sizes of their brains. Dolphin brains, for example, are much more finely grooved than similarly sized human brains.
The second explanation posited that brains fold both as a result of an increasing number of neurons and also as a way to allow this neural growth. The 19th-century neuroanatomist Franz Gall hypothesized that brains folded to allow a much larger cortical surface to fit inside the space of the skull. The alternative would be a cortex that did not fold but expanded like a balloon, an inefficient use of the cramped quarters of the head.
Again, paradoxes abounded. Human cortices have three times the number of neurons than elephant cortices, yet human brains are half the mass and far less folded. Baboon and pig cortices display equivalent amounts of folding, yet baboons have 10 times as many neurons as pigs do. These outliers seemed to suggest that different species possess different mechanisms to control cortical folding—that is, each species has its own way of growing a brain.
The Science study both disproves those hypotheses and reconciles anomalies like the manatee with a simple physical law. Whether or not a brain folds, Herculano-Houzel says, is pure physics. To model brain folding Herculano-Houzel had graphed a power function derived from the product of cortical surface area and the square root of cortical thickness. Mota had recognized that the same model that predicted the degree of brain convolution also explained the crumpling of paper balls.
To see their results you can run essentially the same experiment as the experimenters conducted using four sheets of paper. The cerebral cortex, which is the most superficial part of the hemispheres and is only a few millimeters in thickness, is composed of gray matter, in contrast to the interior of the hemispheres, which is composed partly of white matter.
The exterior surface of the cerebrum, the cerebral cortex, is a convoluted folded grayish colored layer known as gray matter. The convolutions are made up of ridge like bulges gyri separated by small grooves called sulci and larger grooves called fissures. Gray matter which consists of unmyelinated nerve cell bodies, composes the cerebral cortex or outer portion of the cerebrum. Beneath the cortex lies the white matter or myelinated axons.
During embryonic development, the cortex folds upon itself to form gyri folds and sulci shallow grooves so that more gray matter can reside within the skull cavity and giving the brain its distinctive look. The cerebral cortex is the structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. Gray matter is formed by neurons and their unmyelinated fibers, whereas the white matter below the gray matter of the cortex is formed predominantly by myelinated axons interconnecting different regions of the central nervous system CNS.
The human cerebral cortex is between 2 to 4 mm thick. The Cerebrum. The cerebrum is divided into two major parts: the right and left cerebral hemispheres or halves at a fissure, the deep groove down the middle.
The cerebral cortex is connected to various subcortical structures like the thalamus and the basal ganglia, sending information to them along efferent connections and receiving information from them via afferent connections. Most sensory information is routed to the cerebral cortex via the thalamus. Olfactory information, however, passes through the olfactory bulb to the olfactory cortex or piriform cortex.
The vast majority of connections are from one area of the cortex to another rather than to subcortical areas. Cortical regions known as associative cortex are responsible for integrating multiple inputs, processing the information, and carrying out complex responses.
Sensory Areas are the areas that receive and process information from the senses. The parts of the cortex that receive sensory inputs from the thalamus are called primary sensory areas. The senses of vision, audition, and touch are served respectively by the primary visual cortex, primary auditory cortex and primary somatosensory cortex.
In general, the two hemispheres receive information from the opposite contralateral side of the body. Motor Areas are located in both hemispheres of the cortex. They are shaped like a pair of headphones stretching from ear to ear. The motor areas are very closely related to the control of voluntary movements, especially fine fragmented movements performed by the hand. The right half of the motor area controls the left side of the body, and vice versa.
In studies with brain surgery patients, stimulating areas of the motor cortex with tiny electrical probes caused movements. It has been possible for researchers to actually map out the motor cortex quite precisely. The lowest portions of the motor cortex, closest to the temples, control the muscles of the mouth and face. The portions of the motor cortex near the top of the head control the legs and feet. Behind the frontal lobe is the parietal lobe from a Latin word meaning wall.
It includes an area called the somatosensory cortex , just behind the sulcus separating this lobe from the frontal lobe. Again, doctors stimulating points of this area found their patients describing sensations of being touched at various parts of their bodies.
Just like the motor cortex, the somatosensory cortex can be mapped, with the mouth and face closest to the temples and the legs and feet at the top of the head. At the side of the head is the temporal lobe from the Latin word for temple. The special area of the temporal lobe is the auditory cortex. As the name says, this area is intimately connected with the ears and specializes in hearing. It is located near to the temporal lobe's connections with the parietal and frontal lobes.
At the back of the head is the occipital lobe. At the very back of the occipital lobe is the visual cortex , which receives information from the eyes and specializes, of course, in vision.
The areas of the lobes that are not specialized are called association cortex. Besides connecting the various sensory and motor cortices, this is also believed to be where our thought processes occur and many of our memories are ultimately stored. If you are interested in more details about the lobes, click here! If you look at the brain from the top, it becomes immediately obvious that it is split in two from front to back.
There are, in fact, two hemispheres, almost as if we have two brains in our heads instead of just one. Of course, these two halves are intimately linked together with an arch of white matter called the corpus callosum. In various ways, researchers have discovered that the two halves do have some specialization. It is the left hemisphere that relates to the right side of the body generally , and the right hemisphere that relates to the left side of the body.
Also, it is the left hemisphere that usually has language, and seems to be primarily responsible for similar systems such as math and logic. The right hemisphere has more to do with things like spatial orientation, face recognition, and body image. It also seems to govern our ability to appreciate art and music.
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