Innovations of the nineteenth century transformed philosophical psychology into scientific psychology.
From ancient times thinkers had proposed speculative theories of how mental processes were linked to the brain and nervous system. However, not until the nineteenth century did physiology, including neurophysiology, make real progress. By the time scientific psychology began, a general, if limited, picture of neural and brain processes had emerged from two parallel tracks of research. One track was driven by disputes about whether mental functions were localized in different parts of the cerebral hemispheres, beginning with the work of Franz Joseph Gall (1758-1828). Although often reviled as a charlatan. Gall is now widely regarded as the first neuroscientist, possessing a sound orientation, fatally flawed by a mistaken method. Gall proposed that the brain, including the cerebral hemispheres, was a collection of distinct biological organs, each housing a different active mental ability such as language, or behavioral tendency such as lust.
Gall’s system, which he never named, was both fresh and forward looking. Earlier reasoning about brain and mind had imposed philosophical theories on conjectures about the brain. Gall discarded philosophy for the direct examination of the brain. Even his critics conceded that Gall was a brilliant anatomist of both human and animal brains. Gall was the first behavioral psychologist, inspecting brain and behavior instead of introspecting consciousness. His biological orientation led him to look at mental faculties as adaptive brain functions, anticipating post-Darwinian psychology. Unlike philosophers, particularly the idealists who believed the self was identical in everyone, Gall studied individual differences, a major pursuit of modern psychology.
However, Gall’s erroneous method and the pseudo-science of phrenology that his followers built around it tainted his thesis of localization. Lacking modern methods for studying the brains of living organisms, Gall tried to correlate differences in peoples’ mental abilities with the sizes of different areas of the brain. He thought that large brain areas would create hills on peoples’ skulls and small areas would leave valleys. Thus, he studied murderers and musicians, for example, looking for the cranial hills that housed murder and tune. Beginning with J. C. Spurzheim (1776-1832), phrenologists turned Gall’s tentative science of brain and mind into the first popular psychology. They speculatively finished Gall’s map, teaching their devotees how to know themselves and others by reading the bumps on their heads. Phrenology was especially popular in the United States, where its concerns for individual differences and use of psychology in the service of business and social reform foreshadowed the course of German psychology in pragmatic America.
The manifest silliness of phrenology provoked rejection of the idea of localization of function by establishment thinkers. Alexander Bain, for example, systematically examined the claims of phrenologists and argued that associationism could account for the same facts without the hypothesis of separate cerebral organs. The prestigious French scientist Pierre Flourens (1794-1867) attacked the idea of localization of brain function. On the basis of rather crude experiments, he advanced the thesis of equipotentiality, arguing that the cerebral hemispheres act as a mass, having only one function, thought. or intelligence. Phrenology was pushed to the dim margins of scientific respectability, and the idea of localization of cerebral function was temporarily suppressed.
The other track in neuroscience concerned the nervous system. Luigi Galvani (1737-1798) demonstrated that nerves conduct impulses by electricity rather than by “animal spirits” as earlier believed. Franqois Magendie (1783-1855) experimentally demonstrated that nerves transmit impulses only in a single direction: afferent (sensory) nerves carry impulses to the spinal cord and brain, and efferent (motor) nerves carry impulses from the brain and spinal cord to the muscles. British physician Charles Bell (1774-1842) may have independently proposed this hypothesis. Over the course of the century many scientists contributed to understanding the nervous system at the level of the cell, or individual neuron, and to formulating the concept of the synapse, the small gap across which neurons communicate.
Meanwhile, the thesis of localization of function gradually regained respectability. An important discovery was made in 1861 by the clinical neurophysiologist Pierre Paul Broca (1824-1880), who was able to show a connection between damage to a specific area of the left cortex (now called Broca’s area) and loss of a specific mental ability, language. In 1870, Gustav Fritsch (1838-1927) and Eduard Hitzig (1838-1907) experimentally demonstrated localization in a dog’s brain, and a “new phrenology” was born. However, the localized functions revealed by their experiments were not those of Gall. Instead of active brain organs such as theft, Fritsch and Hitzig discovered centers that controlled specific movements of the dog’s limbs.
The two tracks merged into a general picture of the brain and nervous system influentially summarized in Sir David Ferrier’s (1843-1928) The Functions of the Brain (London, 1876). Afferent neurons carry sensory information to the brain, whose specialized sensory areas represent the world. Neurons in the so-called association cortex connect the sensory centers to motor centers, which send out efferent signals controlling responses to stimuli. This conception of brain and nervous system was tailor-made for integration with associationism. As the brain was a reflex device linking stimulus and response, the mind was an associative device linking sensations together and linking sensations with actions. This integration was offered by many European writers, in Britain most notably by Alexander Bain. Psychology seemed to have a sound material basis on which to erect a natural science.
Ultimately, the reflex theory of the brain proved too simple. For example, it knew nothing of the rich neurochemistry by which the brain operates. More importantly for early psychology, it rejected Gall’s notion that the brain was a collection of organs actively causing behavior, accepting, instead, the Cartesian understanding of machines as simple push-pull devices. The reflex theory saw the brain as like an old-fashioned telephone switchboard, passively connecting incoming stimulus with outgoing response. The causes of behavior lay in the environment containing the stimuli to which organisms react, not in the brain or its mind. The reflex theory of the brain added to the specter of materialism by seeming to make free will impossible.
The reflex theory, often allied to empiricism and associationism, constrained psychological theory for a century. An example is James’s famous theory of emotion, first proposed in the 1880s, and adumbrated and defended in Principles. James said that the origins of emotion lie not in the brain, but in behavior: We do not run from a threat because we feel afraid, we are afraid because we find ourselves running from it. Through most of the twentieth century, psychologists proposed stimulus-response theories of behavior to match their conception of the brain. Not until the computer metaphor replaced the switchboard metaphor in the 1970s did the stimulus-response reflex model die.