Some Revolutions in Neuroscience Charles Gross Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/25/1/4/1778565/jocn_a_00308.pdf by MIT Libraries user on 17 May 2021 Abstract ■ In the long history of the study of the nervous system, tics and strategies for studying it. These may be termed there have been a number of major developments that Revolutions in Neuroscience. This essay considers eight of involved radical and permanent changes in fundamental these, ranging from the 6th century BCE to the end of the beliefs and assumptions about the nervous system and in tac- 20th century. ■ THE PRE-SOCRATIC PHILOSOPHERS AND THE IDEA OF SCIENCE and Democritus. Many of them were interested in sensory processes as sources of knowledge. The pre-Socratic philosophers were responsible for the The first writer to advocate the brain as the site of very idea of formal science: the idea that the physical sensation and cognition was the pre-Socratic Alcmaeon of and biological universe was governed by consistent and Croton, a Greek colony in what is now southern Italy. He universal laws that were amenable to understanding by is said to have written: human reason. This was a revolutionary change from the previous prevailing view of the universe as a plaything The seat of sensations is in the brain. This contains of gods and ghosts acting in an arbitrary and capricious the governing faculty. All the senses are connected fashion. in some way with the brain; consequently, they The pre-Socratics lived in the 6th–4th century BCE in are incapable of action if the brain is disturbed or various Greek city-states. They called themselves “physio- shifts its position, for this stops up the passages logia,” which is best translated as “natural philosophers.” through which senses act. This power of the brain They conceived their inquiries as demanding rational to synthesize sensations makes it also the seat criticism and public debate and involving observation and of thought: the storing up of perceptions gives measurement (systematic experimentation especially in memory and belief, and when these are stabilized biology would be almost unknown for several centuries). you get knowledge (Theophrastus, 1917). The earliest pre-Socratics were Thales, Anaximander, and Anaximenes. All three came from the city of Miletus, Alcmaeon is reported to have been the first to use a Greek city-state in Ionia on the West shore of modern dissection as a tool for intellectual inquiry. He dissected Turkey, and thus are often known as Milesians or Ionian the eye and described the optic nerves and chiasm and philosophers. There are several likely reason why Miletus suggested that they brought light to the brain. He ob- was the “cradle of science.” It was a wealthy port city, served phosphenes after a blow to the head and inferred which brought together products and ideas from Greek, that the eye contained light and that this light was neces- Phoenician, and Egyptian sea traders and caravan mer- sary for vision, a view only disproved in the middle of the chants from as far as India and China. Power was moving 18th century. from the landed aristocracy to the merchant classes inter- Democritus is among the other pre-Socratic philoso- ʼ ested in new techniques and concepts. In this new city- phers who extended Alcmaeon s views on the functions state, there was open debate about the nature of society of the brain. He taught that everything in the universe is and the world. composed of atoms. The psyche (soul, mind) is made up These early natural philosophers sought fundamental of the lightest, most spherical, and fastest-moving atoms. principles underlying the universe. For example, Thales Psychic atoms are found mostly in the brain. Slightly cruder thought that water was fundamental, whereas Anaximenes atoms are found in the heart, making it the center of emo- argued for air as the basic element and discussed the tion, and still cruder ones are in the liver, making it the ʼ various forms it might take. Among the other major pre- seat of lust. This trichotomy developed into Plato s hier- Socratics were Heraclitus, Pythagoras, Empedocles, Zeno, archy of the parts of the soul, and through his treatise, “Timaeus” was very influential into the 18th century. The various pre-Socratic natural philosophers had a Princeton University variety of views on the nature of the universe, the body, © 2012 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 25:1, pp. 4–13 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn_a_00308 by guest on 28 September 2021 and the brain. What they held in common was the view the brain, a clear statement of Mullerʼs doctrine of spe- that these could be understood by the use of observation cific nerve energies. Galenʼsdescriptionsofthegross and reason. This assumption was a revolutionary one, anatomy of the brain were very accurate, particularly with marks the beginning of formal science in the West, and respect to the ventricles and the cerebral circulation, is still the basis of modern science. which are both important in his physiological system. This account is based on Gross (1998); the translations Galen usually presented his dissections as if they were of of Freeman (1954); the accounts of Longrigg (1993), Lloyd the human, but in fact, except for the osteological ones, (1970), Sigerist (1961), Sarton (1959), and Farrington they were invariably of animals, which are usually the ox (1944); and the appreciations of Popper (1969) and in the case of brain anatomy, the Barbary “ape” (the Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/25/1/4/1778565/jocn_a_00308.pdf by MIT Libraries user on 17 May 2021 Schrodinger (1954). macaque M. sylvana) for cranial nerve anatomy, and pigs Systematic rational inquiry into the nature of the universe for vivisection. (He did not like to vivisect monkeys arose in China at about the time as the pre-Socratics, but because, he said, of the expressions of their faces when the two traditions are rather different (Lloyd & Sivin, 2002; he did so.) It was only very recently when Galenʼsde- Lloyd, 1996) and had little interaction for many centuries. scriptions were evaluated in terms of the actual species dissected that their great accuracy was recognized (Rocca, GALEN AND THE EXPERIMENTAL 2003). ʼ INVESTIGATION OF THE NERVOUS SYSTEM However, Galen s truly revolutionary work was in car- rying out the first systematic experiments on the func- Galen of Pergamon (129–213 CE) was, by far, the most tions of the nervous system. Galen realized that the important physician, anatomist, and physiologist of clas- spinal cord was an extension of the brain. In his brilliant sical antiquity. His ideas were so pervasive that Western and systematic experiments on sectioning the cord, he medicine well into the 18th century largely saw the struc- compared the effects of hemi-transection and total tran- ture and function of the body through his eyes. Today, section at different levels and noted that injuries inter- his voluminous writings provide a vivid account of the fered with sensory and motor function below the level controversies and achievements of the 600 years of clas- of the section, that hemisection affected only one side, sical biology and medicine. and that sagittal section did not produce paralysis. He Galen was the first to carry out systematic experiments accurately described the different roles of the spinal on the nervous system, thereby initiating a major revolu- nerves in respiration. He even came very close to the tion in the study of the nervous system. Before Galen, Law of Spinal Roots: “The physicians do not even know there were only a few isolated examples of systematic that there is a special root at the origin of the nerves experiments such as in acoustics, those of Strato and Hero which are distributed to the entire hand and from which on vacuums and Ptolemy on optics. In biology and medi- sensation arises; [nor do they know] that there is another cine, observation and dissection were the only methods of root for the nerves moving the muscles” (Galen, 1962). investigation, unless one wants to consider trying out pos- Galen used piglets in his experiments on brain lesions. sible poisons on prisoners as a type of experimentation. He found that anterior brain damage had less deleterious Galen was born in Pergamon, which is now the Turkish effects than posterior. He viewed sensation as a central city of Bergama, and studied medicine there. His first process because he knew from his clinical observations three medical treaties were published while he was a medi- and animal experiments that sensation could be impaired cal student. (Although most of his writing was lost, the by brain injury even when the sense organs were intact. extant ones comprise 22 large volumes, more are discov- Because animals could survive lesions that penetrated to ered every few years and many are still untranslated into the ventricles, Galen thought that the soul was not located English). He then continued his medical studies in several there but rather in the cerebral substance. He taught that other medical centers including Alexandria, which was a all mental diseases were brain diseases. leading center of medical research. He then returned to Galenʼs most famous experiment was the public dem- Pergamon as the physician to the gladiatorial school there onstration of the effects of cutting the recurrent laryngeal where he acquired considerable clinical experience. When nerve on squealing in a pig. Although the encephalocentric the “games” were closed, Galen moved to Rome where he view that the brain controlled sensation, movement, and rapidly rose in medical and social circles, eventually serving cognition remained strong in the Greco–Roman medical as physician to four Roman emperors starting with Marcus community, the opposing cardiocentric view that the heart Aurelius.