Near infrared light
Absorption of light by blood
Cerebral Cortex
The brain is composed of the cerebrum, the diencephalon, the cerebellum, the pons and so on. All of these are covered with a membrana cerebri, a thin and tough skin, floating in cerebrospinal fluid; and these are all packed in the cranium. The cerebral cortex is located about 20 mm beneath the scalp on the cerebrum. Its surface is covered with a mass of nerve cells and capillary vessels. Cerebral cortex is divided into several lobi, separated by sulci. Human beings have the most developed cerebrum compared with the other animals. The differentiation and stratification of the cortical neurocytes is proportional to the degree of evolution.
The cerebral cortex performs sophisticated brain functions. It is sensitive to sound and light, controls motor activities, and processes thought. These areas are unevenly distributed on the cortex. But in particular, high level brain activities, such as "volition", "understanding", "memories", "speech" and so on, are performed in co-operation with several areas mentioned above, and thought to perform in other areas called "association areas".