(I) Localization Theory
The theory of brain localization suggests that human psychological functions are related to specific parts of the brain.
1. Localization theory originated from the phrenology of Gall and Spurzheim in 18th-century Germany, which stated that a person's brain structure reflects certain characteristics and is reflected in the skull. Although phrenology lacks scientific basis, it inspired the idea that brain functions are localized.
2. The true theory of localization was proposed in the 1960s through the study of aphasia. The discoveries made by Broca and Wernicke led people to believe that language has specific brain areas.
3. Canadian doctor Penfield used electrical stimulation of the temporal lobe and found that it could evoke memories of childhood experiences, supporting the theory of localization.
(II) Holism Theory
1. The holism theory was first proposed by Flourens, who believed that the human brain functions as a whole and acts through the whole.
Flourens used the method of partial destruction to remove a part of the brain in animals (chickens and pigeons) for experiments to observe its effects on animal behavior. The results showed that the loss of brain function in animals was not related to the location of cortical removal, but to the size of the cortical removal.
2. In the early 20th century, Lashley further damaged the brains of small white mice to observe their effects on the mice, and concluded:
(1) Principle of equipotentiality: Different parts of the cerebral cortex have almost equal influence on learning.
(2) Principle of mass action: The efficiency of learning is inversely proportional to the size of brain damage, regardless of the location of the damage.
(III) Functional System Theory
Soviet neuropsychologist Luria, while treating soldiers with brain injuries during World War II and conducting rehabilitation training, found that damage to a specific brain area does not lead to the loss of isolated psychological functions, but rather causes a syndrome, which is a series of process disorders. During the rehabilitation training, it was found that physiological functions associated with a specific brain injury site are difficult to restore, but functional transformation is possible. Therefore, the theory of functional systems was proposed.
The brain is a dynamic structure and a complex dynamic functional system. It includes:
1. First functional system: Motor system (activation system).
Consists of the reticular formation and the limbic system.
Its basic function is to maintain the general arousal state of the cerebral cortex, increase its excitability and sensitivity, and achieve self-regulation of behavior. The first functional system does not process specific information, but provides a background for various activities. When this system is damaged, the activation level or excitability level of the brain will generally decrease, affecting the processing of external information and the regulation of behavior.
2. Second functional system: Information reception, processing, and storage system.
Located in the posterior part of the cerebral cortex, including the occipital lobe, temporal lobe, parietal lobe, and corresponding subcortical tissues.
The basic function of the second functional system is to receive various stimuli from the body and the external environment (including auditory, visual, and general somatosensory stimuli), integrate them in terms of space and time, and store them.
It can be divided into:
(1) Primary areas, which are the direct projection areas of stimuli and have highly specialized functions. Damage to this area will result in the loss of different sensory abilities.
(2) Secondary areas, which integrate information processed by the primary areas and are located near the primary areas. Damage to this area will still allow the organism to retain primary sensory abilities, but varying degrees of agnosia will occur.
(3) Tertiary areas, located at the junction of the occipital lobe, temporal lobe, and parietal lobe, are responsible for the spatial and temporal integration of information and reflect the relationships between things. Damage to this area will result in the loss of the ability to integrate simultaneous spatial information.
3. Third functional system: Behavioral regulation system.
The third functional system includes a large area of the frontal lobe and is the system responsible for organizing, regulating, and controlling behavior.
It can be divided into:
(1) Primary areas, located in the primary motor area in the precentral gyrus, are the direct projection areas for movement. Instructions from the brain directly regulate the movement of different parts of the body through this area.
(2) Secondary areas, located in front of the motor area, are mainly responsible for organizing movements and formulating movement programs.
(3) Tertiary areas, located in front of the frontal lobe, are mainly responsible for generating intentions for activities, forming behavioral programs, and regulating and controlling complex forms of behavior. When this brain area is damaged, patients will experience different forms of behavioral disorders.
Luria believes that the three functional systems of the brain interact and coordinate their activities, ensuring the completion of various psychological and behavioral activities through division of labor and cooperation.
(IV) Modular Theory
In the 1980s, the theory of brain modules emerged in the research of cognitive science and cognitive neuroscience. This theory suggests that the human brain is composed of highly specialized and relatively independent modules in terms of structure and function, and the combination of these modules forms the basis for cognitive functions. This theory is supported by the research results of cognitive neuroscience.
(V) Neural Network Theory
This theory suggests that various psychological activities, especially complex cognitive activities, are realized through the coordinated activity of different brain areas, and these brain areas can participate in different cognitive activities through different neural networks and play different roles.
The dynamic neural networks formed by these brain areas constitute the neural basis of various complex cognitive activities. Geschwind was a neuroscientist who used the neural network perspective to describe language production at an early stage of using neural networks.