Brain: Intellectual Functions
The cerebral cortex, or gray matter, is the most external layer of the brain of vertebrates, constituting the largest portion of the nervous system. It is connected to the thalamus, forming the thalamocortical system, which, except by some sensory olfactory pathways to the cortex, constitutes the major two-way unit between sensory perception and intellectual functions in humans. The cortex is divided into several cortical areas, each responsible for separate functions, such as planning of complex movements, memory, personality, elaboration of thoughts, word formation, language understanding, motor coordination, visual processing of words, spatial orientation, and body spatial coordination.
Sensations received from peripheral sense organs by the primary motor and sensory cortical areas are detected as specific sensations (visual, somatic, auditory). The secondary sensory areas are activated in the process of recognition of these signals, and begin the analysis of sensory signals, such as the interpretation of color, shape, and texture. As for somatic sensations, the secondary motor areas recognize patterns of motor activity. However, large areas of the cortex, termed association areas, have a more flexible role than the rigid primary and secondary areas mentioned so far. The association areas of the cortex receive and simultaneously analyze multiple sensations received from several regions of the brain, such as the motor and sensory cortical areas, and subcortical areas such as the limbic system, responsible for animal behavior, emotions and motivation.
The association areas are identified as two major areas, the parieto-occiptotemporal, and the prefrontal association areas. The parieto-occiptotemporal area occupies the large parietal and occipital cortical space, bordered by the somatosensory, auditory, and visual cortices. The second association area is the anterior section of the cortex, bordered by the olfactory lobe, the limbic, and the motor areas. The parieto-occiptotemporal cortex is divided in the following sub areas, in accordance with their respective functional roles: analysis of special body coordinates; language understanding (also known as Wernicke's area); reading; naming of objects. These functions are essential for the learning process and intelligent activity. The prefrontal cortex works in close association with the motor cortex and the parieto-occiptotemporal association area, from which it receives pre-analyzed sensory information. From these data, it processes the planning of sequential and complex patterns of motor-coordinated activity and the elaboration of thoughts. The prefrontal area contains a special region termed Broca's area, where a neural circuitry, responsible for word formation, works in close relationship with the Wernicke's area. Another region of association activity, the limbic association area, is localized in the limbic system (the source of emotional drives, behavior, and motivation) and stimulates the other association areas of the brain.
The brain is divided in two large lobes, interconnected by a bundle of nerves, the corpus callosum. It is now known that in approximately 95% of all people, the area of the cortex in the left hemisphere can be up to 50% larger than in the right hemisphere, even at birth. Both Wernicke's and the Broca's areas are usually much more developed in the left hemisphere, which gave origin to the theory of left hemisphere dominance. The motor area for hand coordination is also dominant in nine of out ten persons, accounting for the predominance of right-handedness among the population. However, the nature of such hemisphere dominance is associated with the linguistic abilities, which is just one of the many aspects linked to intellectual activity. The non-dominant hemisphere is responsible for other important forms of intelligence as well. Moreover, the interpretative and motor areas of the brain do receive sensory information from both the right and the left hemispheres through the corpus callosum. Studies show that the non-dominant hemisphere plays an important role in musical understanding, composition and learning, perception of spatial relations, perception of visual and other esthetical patterns, understanding of connotations in verbal speeches, perception of voice intonation, identification of other's emotions and mood, and body language.
Memory is another fundamental aspect of brain intellectual function, because the learning process and the ability to elaborate abstract thoughts into an ordered and coherent sequence depend upon the memory-processing centers of the brain. Memory-processing centers include the prefrontal cortex for short-term memory, and the intermediate and long-term memory centers of the hippocampus. The hippocampus is an elongated portion of the cerebral cortex belonging to the limbic system, which is responsible, among other functions, by the storage of verbal and symbolic types of memory into both intermediate and long-term memory.
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