This limbic

This limbic area helps to control behavior, which is discussed in detail in Chapter Inability to Progress Toward Goals or to Carry Through Sequential Thoughts. We learned earlier in this chapter that the prefrontal association areas have the capability of calling forth information from widespread areas of the brain and using this information to achieve deeper thought patterns for attaining goals. If these goals include motor action, so be it. If they do not, then the thought processes attain intellectual analytical goals. Although people without prefrontal cortices can still think, they show little concerted thinking in logical sequence for longer than a few seconds or a minute or so at most. One of the results is that people without prefrontal cortices are easily distracted from their central theme of thought, whereas people with functioning prefrontal cortices can drive themselves to completion of their thought goals irrespective of distractions. Elaboration of Thought, Prognostication, and Performance of Higher Intellectual Functions by the Prefrontal AreasConcept of a Working Memory. Another function that has been ascribed to the prefrontal areas by psychologists and neurologists is elaboration of thought. This means simply an increase in depth and abstractness of the different thoughts put together from multiple sources of information. Psychological tests have shown that prefrontal lobectomized lower animals presented with successive bits of sensory information fail to keep track of these bits even in temporary memory, probably because they are distracted so easily that they cannot hold thoughts long enough for memory storage to take place.

Finally, people

Finally, people whose corpus callosum is completely sectioned have two entirely separate conscious portions of the brain. For example, in a teenage boy with a sectioned corpus callosum, only the left half of his brain could understand both the written word and the spoken word because the left side was the dominant hemisphere. Conversely, the right side of the brain could understand the written word but not the spoken word. Furthermore, the right cortex could elicit a motor action response to the written word without the left cortex ever knowing why the response was performed. The effect was quite different when an emotional response was evoked in the right side of the brain: In this case, a subconscious emotional response occurred in the left side of the brain as well. This undoubtedly occurred because the areas of the two sides of the brain for emotions, the anterior temporal cortices and adjacent areas, were still communicating with each other through the anterior commissure that was not sectioned. For instance, when the command kiss was written for the right half of his brain to see, the boy immediately and with full emotion said, No way! This response required function of Wernickes area and the motor areas for speech in the left hemisphere because these leftside areas were necessary to speak the words No way! But when questioned why he said this, the boy could not explain. Thus, the two halves of the brain have independent capabilities for consciousness, memory storage, communication, and control of motor activities.

Therefore, this

Therefore, this hemisphere is called the dominant hemisphere. In about per cent of all people, the left hemisphere is the dominant one. Even at birth, the area of the cortex that will eventually become Wernickes area is as much as per cent larger in the left hemisphere than in the right in more than one half of neonates. Therefore, it is easy to understand why the left side of the brain might become dominant over the right side. However, if for some reason this left side area is damaged or removed in very early childhood, the opposite side of the brain will usually develop dominant characteristics. A theory that can explain the capability of one hemisphere to dominate the other hemisphere is the following. The attention of the mind seems to be directed to one principal thought at a time . Presumably, because the left posterior temporal lobe at birth is usually slightly larger than the right, the left side normally begins to be used to a greater extent than the right. Thereafter, because of the tendency to direct ones attention to the better developed region, the rate of learning in the cerebral hemisphere that gains the first start increases rapidly, whereas in the opposite, lessused side, learning remains slight. Therefore, the left side normally becomes dominant over the right. In about per cent of all people, the left temporal lobe and angular gyrus become dominant, and in the remaining per cent, either both sides develop simultaneously to have dual function, or, more rarely, the right side alone becomes highly developed, with full dominance.

This Chapter

This Chapter Cerebral Cortex, Intellectual Functions of the Brain, Learning and Memory type of learning is called skill learning or reflexive learning; it depends on physically repeating the required tasks over and over again, rather than on symbolical rehearsing in the mind. References Baddeley A: Working memory: looking back and looking forward. Nat Rev Neurosci :, Blank T, Nijholt I , Spiess J: Molecular determinants mediating effects of acute stress on hippocampusdependent synaptic plasticity and learning. Mol Neurobiol :, Bookheimer S: Functional MRI of language: new approaches to understanding the cortical organization of semantic processing. Annu Rev Neurosci :, Conlon R, Hobson JA: Understanding the Human Mind. New York: John Wiley, Dash PK, Hebert AE, Runyan JD: A unified theory for systems and cellular memory consolidation. Brain Res Brain Res Rev :, Dick P, Katsuyuki S: The prefrontal cortex and working memory: physiology and brain imaging. Curr Opin Neurobiol :, Dudai Y: The neurobiology of consolidations, or, how stable is the engram? Annu Rev Psychol :, Ehrlich YM: Molecular and Cellular Mechanisms of Neuronal Plasticity. New York: Plenum Press, Guillery RW: Branching thalamic afferents link action and perception. J Neurophysiol :, Haines DE: Fundamental Neuroscience. New York: Churchill Livingstone, Hamann S, Canli T: Individual differences in emotion processing. Curr Opin Neurobiol :, Kandel ER: The molecular biology of memory storage: a dialogue between genes and synapses.