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1. The discovery of the brain

1.1 The long path to Cajal

The brain has always been, and still is, the less known organ of the body. In this conference we will start by reviewing the history of our ignorance, which was really gross until the 19th century. Aristotle was the most important philosopher and biologist of Antiquity, but still, his ideas on the functioning of the brain ha nothing to do with reality. He saw the brain as a refrigerator with the mission of cooling down the blood that was heated in excess by the heart. Galen was the most prominent medic of Antiquity, and his name would eventually design the medical profession. In opposition to Aristotle, Galen did get to dissect brains, never of humans as it was a taboo in Rome, but of goats and other ruminant, so he assigned human brains the same properties as those of caprids, like the thick net of blood vessels under the brain, the rete mirabilis, where the vital spirit (arterial blood) would transform into an animal spirit (this is, the anima), a liquid that would be distributed from the brain to the rest of the body through the nerves, which where pictured as tubes. Later on the 17th century, Descartes continued thinking in terms of animal spirits and the nerves as tubes, although he also dissected animal heads. He gave a hydrodynamic explanation to movement and the ingenious feeling, but it was also wrong. Furthermore, his concept of the soul and crucial role of the pineal gland in the brain was entirely erroneous.

In the first half of the 19th century, Mathias Shleiden and Theodor Shwamm formulated their theory about the cell, and the hypotheses that all leaving creatures were made of cells. Jan Pukinje described the first neurons and dendrites. Wilhelm von Waldeyer guessed that the nervous cells were extensions of the neurons, a rope of axons that where part of them. Thus, the nervous system, and particularly the brain, would not be a mass or continuous network but a discrete system of neurons, in agreement with the general cellular theory. This theory faced fierce opposition until Santiago Ramón y Cajal proved Waldeyer right using Emilio Golgi's methods and tints, to study with unique detail and precision the structure of the neuron and brain, giving birth to modern neurology.

1.2 Opening the black box

Introspective, experimental and behavioral psychology had attempted studying human behavior like a black box system in which stimuli were associated with responses, neglecting the possibility that the brain could have a role in the process. It was necessary to move from a black box theory to a translucent box theory based on underlying mechanisms. A similar thing had happened in physics with the change from phenomenological thermodynamics to statistical mechanics. The idea was associating psychological roles with parts of the brain. This way, in the 19th century, after dissecting corpses of people with aphasia or other language disorders, Paul Broca and Karl Wernicke discovered the areas of the brain that currently hold their names, and which are involved respectively in the production and listening of articulated talk. In the mid 20th century, Roger Sperry, Michael Gazzaniga an others, explored the functional asymmetry of the cerebral hemispheres, which allowed to understand for example the dominant role of the left hemisphere in in right-handed people's language. Later on, already within the last decade, the discovery of mirror neurons by Giacomo Rizzolati has opened new paths for the understanding of phenomena like empathy and compassion.

Nowadays it is no longer necessary to wait for the death of a patient in order to make dissection and learn something about the topography of the brain. From the primitive encephalogram to the most sophisticated techniques, like magnetoencephalography (MEG),computerized axial tomography scan (CAT scan), magnetic resonance imaging (MRI), positron emission tomography (PET) or the images with radioactive xenon (RCBF), we have now a diverse range of instruments that detect where the blood flows while doing a certain task, or how the local electrical activity changes, so that we can assign anatomical locations to psychologic tasks. Nevertheless, knowing where something happens is not equivalent to understanding it. Functional topography hardly leaves the black box ajar. Between the location of decision making, and the discovery and comprehension of how the decisions are made, we still have a long way to cover.

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