S. D. V. Stephens

notes / Basic Neuroscience and Geometry of Neuroscience / chapter 1: Neurons and Signalling / From my notebook

N1 History of Neuroscience

Before the Romans

  • Prehistory: trepanation to release “evil spirits.”
  • Egypt: the heart is the seat of the soul.
  • Ancient Greece: neuroanatomy begins.
    • Hippocrates—the brain is the organ that regulates sensation (derived from dissection).
    • Aristotle—the brain is a radiator (cooler) for the hot blood of the heart, where the self lay; hence the rationality of man (and hence the lack thereof being an issue of the brain).

The Roman Empire

Galen dissected animals. The brain divides into the cerebrum and the cerebellum.

Pasted figure: a photo of a sheep brain seen from above (a superior, top-down view), with the large, folded cerebrum circled at the front and the smaller cerebellum circled behind it.

Galen concluded that the cerebrum must be for memory and sensation (it is soft and impressionable), while the cerebellum must be for muscle control due to its tough nature. Wrong reasons; right conclusions.

Galen bifurcated brains, learning of the hollow, liquid-filled cavities called ventricles, and postulated that these must be the humors (four vital fluids).

Pasted figure: a sheep brain opened from above to expose the ventricles, the fluid-filled cavities inside the cerebrum.

Sensation and movement, Galen concluded, must be initiated via the movement of the humors within/across the ventricles (similar to blood in veins).

The Renaissance

Andreas Vesalius created detailed drawings of the anatomy of the brain based upon dissections. He maintained the ventricular (humor) theory.

17th-Century France

René Descartes was an advocate of the hydraulic, fluid-mechanical theory of brain function. He furthermore posited that mind–body duality governed the intelligence of man.

The 18th Century

The brain consists of white matter and gray matter. The former contains fibers which transmit data/information to the latter. The gross anatomy of the brain is completed.

The gyri (bumps) and sulci and fissures (grooves) of the brain are identifiable in (virtually) all humans. This led to the parceling of the cerebrum into lobes.

Side view of the left cerebral hemisphere, front to the left, showing the frontal, parietal, occipital and temporal lobes, the central sulcus between the frontal and parietal lobes, the Sylvian fissure above the temporal lobe, and the cerebellum and brain stem below.
  • The central sulcus divides the frontal and parietal lobes.
  • The Sylvian fissure divides the frontal and temporal lobes.

The nervous system becomes divided into the central nervous system (CNS) and the peripheral nervous system (PNS).

Pasted figure: a full-body drawing of the human nervous system. The brain (cerebrum, cerebellum, brain stem) and the spinal cord make up the central nervous system; the nerves branching out from them to the rest of the body make up the peripheral nervous system.

By the end of the 18th century:

  • injury to the brain disrupts the senses, motor function, and thought;
  • injury to the brain is usually fatal;
  • the brain communicates to the body via the nervous system;
  • the brain is made up of smaller sections which have different functions.

Nerves as Wires

  • Ben Franklin: electricity.
  • Luigi Galvani: electricity causes movement in muscles.
  • Emil du Bois-Reymond: the brain generates electricity.

These 3 findings in the 18th century led scientists to conclude that the brain used nerves as “wire.”

At the end of the 18th century there was much debate regarding whether nervous signals were bidirectional:

Hand and brain joined by a single nerve, with one arrow labeled senses running from hand to brain and another labeled movement running from brain to hand, posing the question of whether one nerve carries signals both ways.

In 1810 (early 19th century) Charles Bell and François Magendie put this debate to rest. They discovered that just before each nerve attaches to the spinal cord, its fibers divide into two branches/roots, the dorsal root and the ventral root: the former is responsible for the sensorial information coming in, and the latter is responsible for the muscular-electrical motor control going out. This meant that each nerve is a mixture of fibers, and each fiber is unidirectional!

Pasted figure: a segment of the spinal column with the spinal cord running through the vertebrae; on each side a dorsal and a ventral root join to form a nerve, whose fibers (axons) run out to muscle and skin.

There are 31 pairs of spinal nerves, so 62 in all, and each one is formed where a dorsal root and a ventral root join.

Bell took this even further: he conjectured that motor fibers come out from the cerebellum and that dorsal fibers (sensorial fibers) find their destination in the cerebrum. However, like Galen, he lacked formal scientific evidence.

The physiologist Marie-Jean-Pierre Flourens rectified this. Through experiments on birds (severing strategic brain portions) he determined that this was indeed true.

Phrenology

A med student in Austria named Franz Joseph Gall ended up conjecturing one of the most destructive “scientific” theories in history: phrenology.

Definition N1.1 (Phrenology). Phrenology, not taken seriously at the time by scientists, though widely circulated through the new world among the common man, military leaders, kings, queens, and rulers of all sorts, was the belief that the bumps on the skull correlate to the gyri of the brain, and that from measurements of the skull one could map behavioral traits to specific regions of the brain. Furthermore, these skull measurements could therefore tell you about the nature of any given individual or population.

Thus began “scientific” racism!

Flourens became an ardent campaigner against this idea, especially considering the experimental proof that showed otherwise. E.g., the cerebellum controlled motor function and was NOT for “friendship” and whatnot.

Pasted figure: Gall’s phrenological map, a profile of a head with the skull divided into labeled “faculties” such as language (beside the eye), hope, veneration, cautiousness, secretiveness, friendship, and amativeness (at the back of the neck).

Localization of Function

Paul Broca, a French neurologist, used a case study of a man who could not speak but could understand speech as the basis for the conclusion that a region of the brain in the cerebrum (damaged in the patient) was responsible for speech production.

By 1870 Gustav Fritsch and Eduard Hitzig showed that movement was produced by inducing an electric current into the exposed brain of a living dog. Similarly, Hermann Munk, through experimental ablation, found that the occipital lobe regulates vision.

Darwin

Enter Darwin: the most influential scientist, perhaps of all time.

Theory of evolution specialization in animals’ brains can be studied to conclude things about our brain, due to common ancestors.

Cell Theory

1839: cell theory is first posited by Theodor Schwann.

“All tissues are composed of microscopic units called cells.”

There was still much debate (controversy) at the time as to whether the cells of the brain were unique (the nerve cell) and were the basic unit of function of the brain. Did these cells fuse together to create a net similar to blood vessels? If so, then the cell did not account for the basic unit; rather, the net of cells did (as the loss of the part, much like the severing of veins, would result in the complete or partial destruction of the whole).