Neural Bases Of Behavior

It has not always been assumed that the brain is the principal organ concerned with those aspects of the organism variously termed mental, psychologic, or behavioral. Some early Greek physician philosophers placed the soul in the diaphragm, an idea arising from the notion that the vital principle left a man with his final breath at the time of his death. Hence, we speak of death as expiring and the Greek word, phrenos, denoting diaphragm, has become the root of many words connoting mental activity. Others, such as Empedocles, identified the heart as the locus of the mind, psyche.

However, simple observations such as the frequency with which trauma to the head is associated with changes in consciousness and behavior drew the attention of others to the brain. Some of the earliest known recorded accounts of the effects of brain injury on behavior suggested that particular areas of the brain are associated with particular psychologic functions. Thus, the Edwin Smith Surgical Papyrus described speechlessness following penetrating injuries to some parts of the skull but not others. Scattered observations of a similar nature were made by many of the great pioneers of medicine and physiology. However, the bulk of these observations were ignored until recent years as the tradition of philosophical speculation continued to obscure the clinical correlation of alteration of brain morphology with alterations of behavior.

Great impetus was given to the problem of localization of brain functions by the German physician and physiologist, Franz Josef Gall. He believed that he observed an association between certain mental capacities and the prominence of the bony skull overlying different parts of the brain. He reasoned that a local prominence of the bony skull was due to overdevelopment of the underlying brain tissue, which in turn was concerned with one or another of 37 basic mental "faculties." Thus he conceived of the cerebral cortex as consisting of a mosaic of sub-organs, each concerned with a particular psychologic function. Unfortunately, Gall's early conceptions deteriorated into the pseudoscience of phrenology, by which it was supposed to be possible to predict a person's personality by studying the configuration of the bony skull. However, Gall's conceptions, as naive and poorly founded as they were, did stimulate the search for localization of function in the brain and important discoveries soon followed.

In 1861 Broca reported an association between a lesion of the inferior frontal gyrus in the left hemisphere with expressive aphasia, the inability to emit previously learned verbal language in intelligible form in the absence of any impairment of the muscle groups involved in phonation. In 1874 Wernicke reported an analogous area in the superior temporal gyrus in the left hemisphere. Injury here is often followed by receptive aphasia, the impairment of ability to understand previously learned verbal language in the absence of any impairment of the various sensory organs. As more observations were reported, it appeared for a time that Gall's conception of the brain, as a mosaic of discrete areas each with an identifiable function, was near the truth. However, in more recent years evidence has accrued which indicates the oversimplicity of this view. Many later students of the relationship between the brain and behavior have re-emphasized the interrelatedness and interdependence of various brain structures. Space does not permit tracing the controversy between those who emphasized the specific functions subserved by discrete brain areas and those who emphasized the integrated functioning of the brain. The shift in the consensus of opinion in this controversy has not been like the swing of a pendulum back and forth between old views. Rather, it has been a spiral ascent of knowledge, as more has been learned about the functions of anatomically identifiable brain parts, and the interrelationships of these parts to one another within the framework of an organism interacting with its environment through time. Both of these approaches will be apparent in the discussion which follows of some recent conceptions of brain function.

The subject of the relationship of the brain to behavior will not be dealt with comprehensively. Rather, issues of particular importance to a science of human behavior will be briefly reviewed along. with a discussion of the various technics by which these and related problems are being investigated. Before this, however, some essential anatomic facts and concepts must be considered.