The brain is organized into different regions, each responsible for different functions, and in humans this organization is very marked. The largest parts of the brain are the cerebral hemispheres, which occupy most of the interior of the skull. They are layered structures, the most complex being the outer layer, known as the cerebral cortex （大脑皮层）, where the nerve cells are extremely densely packed to allow great interconnectivity. Its function is not fully understood, but we can get some indication of its purpose from studies of animals that have had it removed. A dog, for example, can still move in a coordinated manner, will eat and sleep, and even bark if it is disturbed. However, it also becomes blind and loses its sense of smell — more significantly, perhaps, it loses all interest in its environment, not responding to people or to its name, nor to other dogs, even of the opposite sex. It also loses all ability to learn. In effect, it loses the characteristics that we generally refer to as indicating intelligence awareness, interest and interaction with an environment, and an ability to adapt and learn. Thus the cerebral cortex seems to be the seat of the higher order functions of the brain, and the core of intelligence. The cerebral cortex has been the subject of investigation by researchers for many years, and is slowly revealing its secrets. It demonstrates a localization of functions, in that different areas of the cortex fulfill different functions, such as motion control, hearing and vision. The visual part of the cortex is especially interesting. In the visual cortex, electrical stimulation of the cells can produce the sensation of light, and detailed analysis has shown that specific layers of neurons are sensitive to particular orientations of input stimuli, so that one layer responds maximally to horizontal lines, while another responds to vertical ones. Although much of this structure is genetically predetermined, the orientation-specific layout of the cells appears to be learnt at an early stage. Animals bought up in an environment of purely horizontal lines do not develop neuron structures that respond to vertical orientations, showing that these structures are developed due to environmental input and not purely from genetic predetermination. This is called self-organization of the visual cortex since there is external teacher to guide the development of these structures.
1. The organization of brain is characterized by（ ）.
2. According to the passage, a dog can still move in a coordinated manner, will eat and sleep, and even bark when（ ）is (are) removed.
3. The word “seat” in line 12 of the first paragraph means（ ）.
4. The visual part of the cortex is especially interesting because（ ）.
5. Which of the following headings is the best title for this passage?
