History of the brain

The history of the brain details the development of thoughts, speculations, and ideas as to the function of the central nervous system, over the last five-thousand years.

Early views on the function of the brain, regarded it to be a form of “cranial stuffing” of sorts. In Egypt, from the late Middle Kingdom onwards, in preparation for mummification, the brain was regularly removed, for it was the heart that was assumed to be the seat of intelligence. According to Herodotus, during the first step of mummification: ‘The most perfect practice is to extract as much of the brain as possible with an iron hook, and what the hook cannot reach is mixed with drugs.’ Over the next five-thousand years, this view came to be reversed; the brain is now known to be seat of intelligence, although colloquial variations of the former remain as in “memorizing something by heart”.

Earliest views
The Edwin Smith Surgical Papyrus, written in the 17th century BC, contains the earliest recorded reference to the brain. The word brain (adjacent), occurring eight times in this papyrus, describes the symptoms, diagnosis, and prognosis of two patients, wounded in the head, who had compound fractures of the skull.

During the second half of the first millennium BC, the Ancient Greeks developed differing views on the function of the brain. It is said that it was the pythagorean Alcmaeon of Croton (VI and V centuries BC) who first considered the brain to be the place where the mind was located. In the 4th BC Hippocrates, believed the brain to be the seat of intelligence (based, among others before him, on Alcmeon's work). During the 4th century BC Aristotle though that, while the heart was the seat of intelligence, the brain was a cooling mechanism for the blood. He reasoned that humans are more rational than the beasts because, among other reasons, they have a larger brain to cool their hot-bloodedness. During the hellenistic period, Herophilus of Calcedonia (c.335/330-280/250 BC) and Erasistratus of Ceos (c. 300-240 BC) made fundamental contributions not only to brain and nervous systems' anatomy and physiology, but to almost every field of the bio-sciences. Their works are today almost completely lost, we know about their achievements due mostly to secondary sources. Their discoveries had to be re-discovered two millenia after their death.

During the Roman Empire, the greek anatomist Galen dissected the brains of sheep, monkeys, dogs, swine, among other non-human mammals. He concluded that, as the cerebellum was more dense than the brain, it must control the muscles, while as the cerebrum was soft, it must be where the senses were processed. Galen further theorized that the brain functioned by movement of fluids through the ventricles.

1600s
In the Age of Enlightenment, René Descartes espoused a fluid mechanical view of the brain similar to Galen's. However, Descartes thought that although this explanation was adequate for the brain functions of animals, the higher mental functions of humans were accomplished by the "soul". This theoretical separation of the mind and brain became known as the mind-body problem, with Descartes espousing the dualist view of the mind as separate from the brain.

In the mid-1600s great progress in describing the anatomy of the brain (neuroanatomy) was achieved by the English anatomist Thomas Willis and Flemish anatomist Vesalius. They dispelled many of the notions of Galen and Descartes, and resolved many facts about the macro structure of the brain.

1700s
In the 1700s, Luigi Galvani showed that electrically stimulating the sciatic nerve of a dissected frog caused movement of the attached muscle. His experiments moved scientists away from the fluid mechanical theory of the brain and toward an electrical theory. In the 19th century, Galvani's work led to research in bioelectricity and to the discovery of the membrane potential and action potential by researchers such as Emil du Bois-Reymond.

1800s
The scientists of the 1800s debated whether areas of the brain corresponded to specific functions or if the brain functioned as a whole (the "aggregate field theory"). Jean Pierre Flourens championed the aggregate field theory in opposition to the pseudoscience of phrenology, founded by Franz Joseph Gall. However, the work of Paul Broca, Karl Wernicke, and Korbinian Brodmann eventually helped to show that areas of the brain had specific functions. Their work showed that, while some functions were repeated, there is also a lateralization of brain function whereby some functions, such as speech and language, are usually controlled by a particular cerebral hemisphere. The redundancy of functioning has come to be known as parallel distributed processing.

1900s
By the 20th century, the anatomical works of Santiago Ramón y Cajal and Camillo Golgi laid the foundation for the study of individual neurons. Charles Scott Sherrington and Edgar Douglas Adrian furthered the study of neurons with the new techniques using electrodes. Neurotransmitters were discovered and investigated by many scientists, including Otto Loewi, Henry Hallett Dale, and Arvid Carlsson. These neurochemicals are responsible for carrying signals from one neuron to another across the tiny gaps (synapses) between the neuronal connections.

In 1929, German physician Hans Berger recorded the first electrical potentials from a living brain. This technique—known as electroencephalography or EEG—led to the widespread use of neuroimaging on live, active humans and animals to study the processes of the mind.

Modern neuroscience is experiencing rapid growth due to the availability of computers capable of handling the intense processing required for understanding such a complex system. Neuroscientists use many different approaches to study the brain at different levels—from the molecules to systems. Considerable knowledge has accumulated about the electrophysiological properties of different types of neurons and their responses to neurotransmitters. Recordings from the brains of awake, behaving animals pioneered by Edward Evarts help to decode neuronal firing during different behaviors and cognitive processes. Miguel Nicolelis introduced multi-electrode recording techniques which led to creation of rudimentary brain-computer interfaces. Rapidly developing neuroimaging techniques such as functional magnetic resonance imaging (fMRI) allows scientists to study the brain in living humans and animals in ways that their predecessors could not.