The human brain contains an average of ten billion neurons or nerve cells, each of which is linked with one thousand to ten thousand other neurons. These nerve cells participate in countless electrical microcircuits which make possible thought, perception, communication, and other types of mental activity.// The outside surface of the brain, which is known as the cortex, consists of a thin wrinkled mantle of gray tissue made up of millions of neurons. This layer of the brain represents man's relatively recent evolutionary step in neurological development and is not present to a comparable degree in any other species.// The brain is divided into two roughly symmetrical hemispheres, sometimes called right and left brains. The activity of the two hemispheres is coordinated by a number of interconnecting nerve pathways. The two sides of the brain, while fairly comparable in size and form, appear to specialize in handling various tasks.// Current evidence suggests that the left and right hemispheres differ in some way in their function. For example, specialized linguistic and perceptual skills are each associated with a particular hemisphere of the brain. In most individuals, the left hemisphere has primary responsibility for language, while the right hemisphere controls visual and spatial skills as well as the perception of nonlinguistic sounds and musical melodies.//

　　人的大脑平均有100 亿个神经元，或者叫做神经细胞。每个神经元与其它一千至一万个神经元相连。神经元从事着不可悉数的微电路脉冲活动，并由此产生思维，感觉，交流以及一些其他脑力活动。//大脑的外皮层叫做脑皮层，脑皮层很薄，有褶皱，是一层由数百万计的神经元组成的灰色组织。脑皮层代表着人类在其神经发展的历史长河中近期的进化，任何其他物质的脑皮层都无法和人类的脑皮层相提并论。// 整个大脑分为两个大致对称的半球，有时被称为右半脑和左半脑。一些互为联系的神经束对这两个脑半球活动进行协调。大脑两个半球虽然有着相似的尺寸和形状，却各司其职。//据目前所知，两个脑半球有着不同的功能。例如：语言能力和感知能力隶属于不同的半球。大多数人的左半球负责语言操作，而右半球则掌管与视觉和空间相关的技能，负责对非语言声音以及音乐的感知。//