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Before the 1980s, consciousness had belonged to the fields of philosophy and psychology. It was difficult for neuroscientists to get funded for the study of this ethereal thing. As a matter of fact, consciousness arises from brain activity, it should be a subject of neuroscience. We all know that general anesthesia can cause unconsciousness. What happened to the brain at this time? Is a vegetative person conscious? How is his brain different from anesthetized person? In the past few decades, by using advanced neuroimaging technology, neuroscientists have been able to explore consciousness along this line, and have made considerable progress.
Figure 31a. The main areas of the human brain. [Source: NIH]
The human brain can be divided into three parts: brainstem, cerebellum and cerebrum. The brainstem is located at the base of the brain, connecting the spinal cord with the rest of the brain. It controls heartbeat, blood pressure and breathing that are essential for survival. The cerebellum is located above the brainstem, with weight about 10% of the brain. It plays important roles in balance and coordination.
The cerebrum has two hemispheres, accounting for 85% of the brain's weight. The two hemispheres are connected by thick bundles of nerve fibers called the corpus callosum. Each hemisphere has four lobes, with distinct but also linked functions.
The cerebral cortex refers to the outer layer of the cerebrum, with thickness about 2-5 mm. It can be subdivided into isocortex (neocortex) and allocortex (paleo- and archicortex). The neocortex consists of six horizontal layers, designated as I, II, III, IV, V, VI (Figure 31b). The allocortex contains fewer than six layers in most regions, but can also have six layers in some areas such as entorhinal cortex. The hippocampus belongs to the allocortex.
The limbic system is located at the border (limbus) between cerebral cortex and the brainstem. It includes the following structures:
Author: Frank Lee