Intoxicating Minds: How Drugs Work (Maps of the Mind) by Regan Ciaran

Author:Regan, Ciaran [Regan, Ciaran]
Language: eng
Format: epub
Tags: Medical/Neuroscience, PSY040000, Psychology/Experimental Psychology, MED057000
Publisher: Columbia University Press
Published: 2012-06-18T20:00:00+00:00

A Blueprint for the Brain

The relative size of brain-to-body weight is surprisingly constant among mammals; the ratio is precisely the same for both the elephant and the shrew. The size of the cortex, or those regions that control movement, is also constant when compared to the size of the whole brain. It would seem that genetic instructions for the blueprint of the brain have been conserved during mammalian evolution. This makes good sense. If one part of the brain enlarges, then the size of those parts that work with it may be expected to show a corresponding change in size. But this does not mean that brains are alike in every way. Uniformity allows one to view general features of brain organization, but when examined more closely, an impressive array of specialization exists between species.

Major regions of the mammalian brain are organized for receiving and analyzing information. There are at least a dozen areas in the visual cortex of the brain that respond differently to the attributes of an object, such as its color, size, or movement. The unique use of language by humans is reflected in the development of specific brain regions. Learning a foreign language in adulthood employs a brain area that is distinct from that used in establishing one’s first language. Communication by speech is particularly dependent on working memory, for which the prefrontal lobe has been significantly enlarged. Environmental instructions, however, determine how the nerve cell pathways of these regions will be formed, the nature and use of their synaptic connections, and the extent to which they are stimulated by surrounding circumstances. Unstimulated nerve cells simply die, while unused synapses disappear. Cell death is an important phenomenon in the construction of the mature nervous system, a kind of editing of unnecessary connections.

But experience continues to tune this rough-and-ready apparatus for its precise job. The cortical regions that receive and process information are not static—they can change. Learning can lead to structural alterations in the brain. There appears to be use-dependent competition for cortical territory. The cortical areas that control our movements change as we acquire new skills; they modify their circuits, and, should the skill require new circuits, they encroach on adjacent cortical areas. The architecture of every brain is individually modified because we exercise our skills in different ways. This is the biological basis for experience: it is related to our capacity to know the external world, and it is the biology of human intelligence.

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