Neuroscience History and Philosophy

Prehistoric Views

  • Understanding of prehistoric societies' views on the brain comes from fossil records and instances of trepanation.
  • Fossil records indicate deliberate cranial damage during war, suggesting awareness of the brain's vital role.
  • Trepanation involved cutting into the skull to treat diseases, including mental illnesses, with the belief that it allowed evil demons to leave the body. This practice shows that ancient societies acknowledged the brain's importance in behavior, attributing abnormal behavior to demonic possession.

Ancient Views

  • Egyptians believed the heart was the seat of the soul and discarded the brain during mummification, indicating a lack of appreciation for the brain's importance.
  • Greeks believed the brain was important for sensation and perception. Hippocrates believed the brain was the seed of intelligence, a view not widely held.
  • Aristotle believed the brain's function was to cool the blood, enabling rational thought.
  • Galen, a Greek physician, through treating gladiators and animal dissections, distinguished between the cerebrum (sensation) and cerebellum (movement). He discovered ventricles in the brain containing cerebral spinal fluid and linked them to the four humors theory. Fluid mechanical theory was the popular theory at the time.

Early Modern Views

  • Rene Descartes proposed dualism, suggesting that animal behavior was controlled by the physical brain, while uniquely human mental capabilities were controlled by a metaphysical mind.
  • Descartes believed the pineal gland was where the soul/mind communicated with the brain/body because of its singular, central location.
  • Dissections provided information about gray and white matter, the central vs. peripheral nervous system, lobes of the cerebrum, gyri, sulci, and localization of function.
  • Descartes, in his "Treatise of Man", used fluid mechanical theory to explain animalistic functions, comparing nerves to pipes conducting water in royal gardens and, believing animal spirits pumped into nerves controlled them.

Electrophysiology

  • Luigi Galvani observed that muscles twitch when stimulated with electricity, indicating the importance of electricity in operating muscles through nerves.
  • Emile Dubois-Raymond discovered that the brain generates electricity itself.
  • Charles Bell discovered that nerves conduct bidirectional signals: from the central nervous system to muscles (motor) and from the body to the central nervous system (sensory). Information passes in sensory fashion from the body into the central nervous system to carry sensory information. He found the dorsal side of the spinal cord controlled sensory information, and the ventral side contained motor information.
  • Francois Magendie, similarly, found that the dorsal side of the spinal cord carried sensory information and the ventral side carried motor information via electrophysiology.

Cellular Neuroscience

  • Cell theory was advanced by Theodor Schwann in the early nineteenth century.
  • Camillo Golgi developed a stain to visualize entire neurons (cell bodies, axons, and dendrites) but proposed the reticular hypothesis (brain as a giant web-like structure).
  • Santiago Ramon y Cajal, considered the father of modern neuroscience, used Golgi's stain to disprove the reticular hypothesis, proposing the neuron doctrine (neurons are discrete entities separated by synapses).
  • Cajal created drawings of neurons and synapses, emphasizing the separations between nerves.
  • Otto Loewi discovered the first neurotransmitter, acetylcholine (initially called "vagus stuff"), demonstrating chemical neurotransmission across synapses. Stimulating the vagus nerve slowed the heart, and fluid extracted from that stimulation containing acetylcholine also slowed another heart.
  • Korbinian Brodmann classified the cortex into 52 regions based on cytoarchitecture (numbers and shapes of neurons). His classification is still used today (e.g., Broadman area number one).
  • Donald Hebb proposed that neurons communicate through synapses, which are altered during learning and memory. Hebb's postulate: "neurons that fire together, wire together".
  • Hebbian plasticity underlies learning, where simultaneous activity strengthens connections between neurons.
  • Axon
    earrow Cell A
    earrow Cell B
  • A \rightarrow B
  • Hebb's Postulate (1949): when an axon of cell A is near enough to excite cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency as one of the cells firing B is increased.

Functional Localization

  • Functional localization is the concept that different brain areas perform specific functions.
  • Franz Gall led the movement of phrenology, arguing personality traits could be detected through enlargements/indentations on the head. His work captured the popular imagination for many decades and was sold in thousands of textbooks. This idea led to mistreatment of certain races and practices like slavery, based on false beliefs that skull shapes indicated personality.
  • Jean Pierre Flourens used experimental ablation to contradict phrenology.
  • Paul Broca discovered Broca's area, responsible for language production. A patient who could articulate sounds but could not speak meaningful language had a lesion in the inferior part of the frontal lobe (Broca's area.)
  • Later, it was discovered a separate area was responsible for language reception.
  • Wilder Penfield stimulated the primary motor cortex (M1) and primary somatosensory cortex (S1) during open brain surgery, mapping motor and sensory functions. Stimulating different parts of M1 caused unintentional movement of different body parts, revealing a somatotopic map for motor control. Similarly, stimulating S1 elicited touch sensations in different body parts, revealing a corresponding somatotopic map for sensory information.

Conclusion

  • Neuroscience is a young field, most discoveries have been made in recent decades.