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Modularity in the Nervous System

Figure 4.1:  Spuzheim's Map of Brain Areas (1908).

The idea of a modular mind is very old. Researchers in brain theory have often tried to locate certain functions in the brain. An early attempt to develop a map of the mind was made by J.G. Spuzheim in 1908. In Figure 4.1 his idea is shown, taken from [kala92, p134,]. The methods since then have changed dramatically; also the functions of modules which are proposed are different nowadays. In the following paragraphs a summary of the current view of the brain structuregif is given.

The human central nervous system (CNS) can be subdivided into spinal cord, medulla oblongata, pons, midbrain, diencephalon, cerebellum, and the two cerebral hemispheres. All these parts have their own functions. Each region is interconnected with other parts of the brain. In Figure 4.2 a rough anatomic subdivision of the brain is given; the picture is taken from [barr88, p7,].

Figure 4.2:  Anatomical Subdivision of the Human Brain.

The CNS is also connected by cranial nerves and by the spinal nerves with other regions of the human body. In the peripheral nervous system (PNS) sensory endings and effector endings are included. The interaction of the brain with the environment is realized by the PNS. The sensory nerves (afferent fibers) provide the CNS with information from the environment. The efferent fibers (motor neurons) control the muscles.

It is possible to divide the anatomic regions of the CNS further. The topology of the cerebral cortex is shown in Figure 4.3, from [kala92, p123,]. In the cortex different regions have different higher brain functions. The modules should not be regarded as isolated parts; they are highly connected. The following description is according to [kala92] and [barr88].

Figure 4.3:  Functional Subdivision of the Cortex.

The frontal lobe is the control unit for fine movement (the precentral gyrus). This part is also responsible for appropriate behaviour in accordance with the standards of the individual. Functions of memory and movement planning are located in this area, too.

The temporal lope is the primary processing unit for acoustic information. In this region complex recognition tasks, such as face recognition, are located. The comprehension of language is connected to this area (Wernicke's area).

The parietal lope deals with body sensation. Sensory information from all over the body is processed in the postcentral gyrus. The whole body is mapped onto this area.

The occipital lobe is the primary visual cortex. This area is mainly responsible for vision.

The CNS has also smaller functional units, called nuclei. These are clusters of neurons. Nuclei can be found in the most parts of the CNS. Each cranial nerve originates in a nucleus. This module is a unit to integrate the sensory input and to regulate the motor output.

Different areas in the brain have also a different cellular structure. Some parts consist mainly of cell bodies and dentrites (e.g. the surface of the cortex), this is called gray matter. Other parts are containing mostly myelinated axons, these parts are called white matter.

A modern research method to locate functional units of the brain is to use Positron-emission tomography (PET). The test subject receives an injection of glucose with a radioactive label (with a very short half-live ranging). The regions which are more active need more energy; the concentration of glucose and therefore the concentration of the radioactive label will be higher in these parts than in other parts of the brain. Using PET these regions can be localized. It is assumed that the region which is most active, is the part of the CNS which deals with the task. For a more comprehensive description see [posn88].

The described anatomic structures underline the modular characteristics of the human brain on several levels. The connections and the structure of the modules and their interaction result in intelligent behaviour.

next up previous contents
Next: Modularity Derived from Psychology Up: Modularity Previous: Modularity

Albrecht Schmidt
Mit Okt 4 16:45:34 CEST 2000