It may seem ridiculous today that a great philosopher like Aristotle believed that the heart was the seat of thought and intelligence, and that the brain was simply a radiator to cool the blood. The truth is that not all of his contemporaries were so misguided, and by then others understood the crucial role of the brain in much of what distinguishes us as humans. Today, in what some scientists have dubbed the century of the brain, we are edging closer to the most precise knowledge we have ever had of our governing organ, so much so that we can even visualise it on the Internet with the level of detail of a digital map.
The brain has been the subject of study since classical antiquity, but our understanding of it was crude; it was not until the 16th century that the Belgian anatomist Vesalius correctly understood that its functions resided in the brain mass and not in the ventricles or fluid-filled cavities, as had hitherto been believed. In the 19th century, the work of Paul Broca and Carl Wernicke began to assign certain regions of the brain to certain functions, and in the early 20th century, neuroanatomists such as Santiago Ramón y Cajal began to reveal the fine weave of neurons and their different types. In 1909, the German neurologist Korbinian Brodmann published the first complete map of the regions of the cerebral cortex, based on the organisation of its cellular architecture.
A look inside our most valuable organ
Throughout the 20th century, the introduction of new neuroimaging techniques and advances in computing have led to a spectacular leap in brain mapping. An example of this is the atlas published in 2013 by the BigBrain project, an initiative of the Montreal Neurological Institute and the German research centre Forschungszentrum Jülich. The researchers used the healthy brain of a woman who died at the age of 65 as the source. The organ was first scanned by magnetic resonance imaging and then sectioned into 7,404 slices, each 20-microns thick, using a microtome. Once all the sections were stained and digitised in high resolution using an optical scanner, the computer system was responsible for the digital reconstruction.
After five years of work, the result is a 3D map with a resolution of 20 microns. By way of comparison, this definition is 50 times higher than that achieved by other brain mapping projects such as the Allen Brain Atlas, a project promoted by Microsoft co-founder Paul Allen, which has a resolution of 1 millimetre. The BigBrain atlas is available on the Internet, freely accessible to any user, and the level of zoom it offers makes it possible to see individual neurons.
BigBrain and the Allen Brain Atlas are just two of several initiatives that are tackling brain mapping using different techniques and at different levels of complexity and detail. The Human Connectome Project, funded by the US National Institutes of Health (NIH), gathered neuroimaging data from the brains of 1,200 people to create a connectome, a large map of connections, the highways along which brain processes run. The Human Brain Project, funded by the European Union, comprises diverse initiatives such as BigBrain itself, within an infrastructure aimed at advancing knowledge of the structure and function of the brain and its computational simulation; the US is investing in the BRAIN Initiative of the NIH, while Japan has launched the Brain/MINDS project.
Science has already succeeded in unravelling the brains of simple organisms such as worms in minute detail, but also in fully mapping the brains of notably more complex species such as the mouse. In the large and complicated human brain there is still much terra incognita, but it is a path of exploration that we are pursuing and that is set to transform our knowledge and our ability to fight neurodegenerative diseases, one of the great medical and scientific challenges of the 21st century.