The brain function is to enable the organism to adapt to a changing environment and to survive. The central nervous system receives stimuli from outside and inside the body through the sensory organs; it then filters the stimuli and processes them into information. In accordance with this information, it sends impulses to the periphery of the body so that the organism can react in a meaningful way to the constantly changing conditions. This highly simplified and schematic description is supposed to provide an approximate illustration of the extremely complex interactions among billions of nerve cells. For centuries there has been the simple mechanistic idea that sensations reach the brain and the brain then triggers motor reactions. According to Descartes, optic stimuli are transmitted from the eyes to the pineal gland (epiphysis), which then sends impulses that travel to the muscles. He viewed the pineal gland as the seat of the soul. Franz Gall was the first to postulate the importance of the cerebral convolutions and the cerebral cortex for brain function.
On the basis of brain injuries, Kleist arrived at localizations of higher cerebral functions. He assumed that positive capacities, or “functions,” would correspond to deficits in recognition and thinking, motivation and action, among others, which were expressed as negative pathological findings. However, this is not so. While it is possible to localize symptoms of deficit, this cannot be done for capacities (von Monakow). Critics of this theory of localization and centers spoke of “brain mythology.” Ultimately, specific capacities cannot be attributed to specific brain regions because immense numbers of other neuronal groups are always participating in the stimulation, inhibition, or modulation of a capacity. The socalled “centers” can be regarded, at best, as important relay stations for a particular capacity. Nor is the central nervous system a rigid apparatus; rather it exhibits a considerable degree of plasticity. Especially in the infant brain, other centers can take over and perform functions in place of injured parts of the brain. Plasticity of our principal organ is also a prerequisite for the capacity
to learn (language, writing, physical skills).
Information processing in the telencephalon (cerebrum or brain) is known as integration. It refers to the combination and interconnection of sensations, including stored experience, to form a higher and complex functional unit. In this way, the functions of the organism are guided by means of the meticulous mutual coordination between groups of neurons. During human evolution, the integrative processes of regulating and coordinating elementary biological tasks have developed into conscious recognition, thought, and action. Cybernetics and computer technology have provided us with models for the function of the brain (cognitive science). According to these models, various “functions” are based on the continuously changing stimuli within interconnected neuronal circuits.