Neuropsychopharmacology in Historical Perspective
Education in the Field in the Post-Neuropsychopharmacology Era
Reflexes of the brain
In the third edition of Stedman’s Medical Dictionary, published in 1990, the term “reflex” was defined “an involuntary reaction in response to a stimulus applied to the periphery and transmitted to the nervous centers in the brain or spinal cord” (Stedman 1990). In the current (2017) Merrion-Webster on-line dictionary it is defined an “automatic and often inborn response to a stimulus that typically involves a nerve impulse passing inward from a receptor to the spinal cord and then passing outward from the spinal cord to an effector (such as a muscle or gland) without reaching the level of consciousness and often without passing to the brain.” The concept of a “reflex” implies a “reflex arc,” i.e., a “pathway followed by nerves which carry sensory information from the receptor to the spinal cord, and then carry the response generated by the spinal cord to effector organ(s) during a “reflex.”
The first description of a “reflex,” the one of making a person bat his eyes by aiming a mock blow of them, was given by René Descartes (1596-1650) in his treatise, Des passions de l’ame (Descartes 1649). In his time the action displayed in a “reflex action” was attributed to “vital spirits in the nervous fluid.” It was Johann Bohn (1640-1719) who first, in 1668, recognized on the basis of his findings on decapitated frogs that the action encountered in a “reflex” was entirely “material and mechanical” (Garrison 1929).
Research to detect the structural underpinning of “reflex action,” the “reflex arc,” began in the laboratory of British anatomist Sir Charles Bell (1774–1842) in the early years of the 19th century. He reported his findings in 1811 in his pamphlet “New Idea of the Anatomy of the Brain and Nervous System.” It reads: “On laying bare the roots of the spinal nerves I found that I could cut across the posterior fasciculus of nerves which took its origin from the posterior portion of the spinal marrow without convulsing the muscles of the back, but that, on touching the anterior fasciculus with the point of the knife, the muscles of the back were immediately convulsed.” Bell’s discovery that the anterior spinal roots are involved with “motor function” was in conflict with the belief of his time that “all nerves were sensory: sensible or insensible” (Bell 1811).
Bell’s structural underpinning of the entire reflex arc was independently confirmed and further elaborated by French physiologist Francois Magendie (1783–1855). In 1822, Magendie demonstrated that stimulation of fibers from the dorsal root of the spinal cord caused pain and stimulation of fibers from the anterior root caused motor activity, whereas transection of fibers from the dorsal root abolished pain and transection of fibers from the anterior root abolished motor activity. His findings provided experimental proof for what was to become known as the “Bell-Magendie Law” which stipulates that the posterior (dorsal) spinal nerve roots contain only sensory fibers and the anterior roots only motor fibers. Magendie had also shown that the interaction between the roots is one directional, i.e., from the “posterior roots” to the “anterior roots” (Magendie 1822).
Magendi’s findings in dog puppies were further substantiated in 1831 in rats by Johannes Peter Müller (1801-1858), a German physiologist. By severing the posterior roots of the spinal nerve leading to the frog’s leg, the leg became insensible, but not paralyzed, and by cutting the anterior roots of the spinal nerve leading to the leg, the limb became paralyzed without losing sensation (Müller 1831). Two years later, in 1833, Marshall Hall (1790–1857), an English physician and physiologist, while studying reflex function of the medulla oblongata and medulla spinalis, determined the difference between “volitional actions” and “unconscious reflexes” (Hall 1833).
Stimulated by the ongoing research in physiology in England, France and Germany on the “reflex,” and especially of Magendi’s (1822) recognition of the importance of the “reflex arc” that links sensory input with motor output in the functioning of the nervous system (spinal cord), Wilhelm Griesinger (1817-1878), a German physician, was first to perceive mental activity as “reflex” activity. He was also the first, in 1843, to describe “psychic reflex actions” (psychische Reflexactionen) (Griesinger 1843).
The first indirect-behavioral support for “psychic reflex” was given, in 1852, by Bidder and Schmidt who noted that teasing a dog with food led to gastric secretion. About the same time a similar observation was made by Claude Bernard (1817-1878). He noticed, while collecting gastric secretion from a horse, that after several repetitions the mere fact of his entering the stable provided sufficient stimulus to induce gastric secretion (Ban 1964, 1966).
By adopting the “reflex” as the elementary unit of “mental activity” in 1843, Griesinger set the stage for the development of psychiatry as a medical discipline. Twenty years later, in 1863, Ivan Mihailovich Sechenov (1829-1905), a Russian physiologist who studied “nervous inhibition” in the central nervous system of the frog in Claude Bernard’s laboratory in Paris, elaborated on Griesinger’s descriptions. In his monograph, “Reflexes of the Brain,” he concluded that all activity, including the “psychological” in the brain, is reflex and as such follows fixed laws determinable by investigation (Sechenov 1863, 1935; Wells 1956).
The structural underpinning of the “psychic reflex” was established in the late 19th century by Italian histologist Camillo Golgi (1843-1926), who, in 1874, described multi-polar (Golgi) cells in the “olfactory bulb” with the employment of silver staining; in 1894 Santiago Ramon y Cajal (1852-1934), a Spanish histologist, established that the “neuron” is the morphological and functional unit of the nervous system; and Sir Charles Sherrington (1857-1952), an English physiologist who demonstrated that the “synapse,” a term he coined in 1897, “is the functional site of transmission from one neuron to another (Cajal 1894; Golgi 1874; Pearce 2004; Sherrington 1906).
With Sherrington’s demonstration that the synapse is the functional site of transmission from one neuron to another, the possibility that the “reflex arc” provides the structural basis for the functional activity of the brain has become reality and Griesinger’s perception of mental activity as “reflex activity,” has become a realistic possibility.
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March 22, 2018