The brain has contributed in a very specific way to the construction of operative intelligence. This organ and its structure are a product of the biological, ethological and technological evolution of the genus Homo. The elements contributing to our cerebral tissues' increase in complexity are, apart of the biological evolution, the generic sociability that we posses due to being part of the Hominidae family, and also our extra-somatic adaptation capacity through tools that we conceive and produce with our upper extremities.
The neuromechanical feedback that occurred along the last three million years between our brain and our upper extremities is in our opinion responsible for the morphology and structure of our brain. Thus, the co-evolution of brain and tools, and the posterior conversion of technical capacity to technology, have configured a being with capabilities that no other mammal animal has.
Together with the productions of tools, language is another adaptive capacity that does not appear consistently in other groups of primates. Thus, we need to understand how the human brain has been selected based on the perspective of the association of properties. In opposition to other, the specific contribution of neuromechanics, ability, and language are key elements to understand the social brain of our linage.
The evolution of the genus Homo across the different species that build its phylogenetic tree, in which only our branch remains represented through our species Homo sapiens, offers evolutionary questions about the size and social use of the brain, and the future of our species. The brain of the hominids within our genus has increased from the average 500 cubic centimeters in the Pliocene, around 3 million years ago in the African savanna, to the brain of the Homo neanderthalensis (1600 cc.) and the Homo sapiens (approximately 1500 cc.). With the exception of the Homo floresiensis, which presented an average capacity of 350 cubic centimeters -an epiphenomenom-, the cerebral increase in volume has been fundamental for our social development.
We hope that the socialization of science will allow us to take advantage of having a larger and well structured brain, and that this will facilitate solutions for problems that in the past were only solvable through natural selection, which now cutural selection has qualified into technological culture provoking social circumstances that had never occurred in the past.
For the first time in the historical evolution of our genus, logic and knowledge can substitute the random adaptive processes of the human primates. Hominization and humanization are interrelated processes, although the later has taken the lead within well structured societies. We will see how our brain adapts to the new situations provided by the scientific-technological revolution. Only the transformation of knowledge into thinking can be efficient for our survival in this planet. The brain, thus, continues to be the fundamental organ for the conscience progress of our linage.
One of the main goals of neuroscience is understanding the biological mechanisms responsible of the activity in the human mind. Without doubt, the brain is the most interesting and enigmatic organ of the human body, not only because it governs our organism, but also because it controls our behaviour and allows us to communicate with other living beings. Particularly, the study of the cerebral cortex is the largest challenge of the coming centuries, as it represents the fundaments of our humanity; this is, the activity of the cerebral cortex is related with the capacities that differ humans from the rest of mammals. Thanks to the notable development and evolution of the brain, we are capable of doing extraordinary and extremely complex tasks such as writing a book, composing a symphony or inventing a computer. Without doubt, science has advanced dramatically in the last decades allowing us to study the human brain from all kind of angles -molecular, morphology, physiology and genetic-, although we have only come to scratch the surface of mysteries it holds. Even if it may sound surprising, we still lack answers to many of the basic questions in neuroscience, such as: What is the neuronal substrate that makes us humans? How is the brain altered, and how diseases like schizophrenia, Alzheimer, or depression are produced? How does the brain integrate simultaneously the information that is processed in the different cortical areas in order to provide us with a unified, continuos and coherent perception? All these fundamental questions, and many others, still lack answer even though we are witnessing many scientific advances in the present.
Among the favorite topics of Cajal was the study of the human neocortex and the butterflies of the soul, as he beautifully described in a metaphoric sense the pyramidal cells. Currently, we are aware that pyramidal cells are the main source of cortical exciting synapses and virtually the only projecting cell of the cerebral cortex. Thus, the information processed in a certain region of the cortex is transported from there through the axons of the pyramidal cells in order to reach other regions of the cortex or subcortical centres. On top of that, they are also the key elements for the columnar organization of the cerebral cortex, and of the linkage mechanisms in the global process of sensory perception. These are some of the reasons why the study of pyramidal cells is of maximum interest. Furthermore, the dendritic spines of the pyramidal cells are a crucial component for the structure and roles of these cells, which explains why this is one of the main lines of research in the present.
Comparative studies between the different cortical regions and between species, mainly between humans and non-human primates, have been done by applying sophisticated methodologies to analyze pyramidal cells. For example, it has been observed that the pyramidal cells from from the human temporal cortex have approximately twice the dendritic spines of a macaque or a titi monkey, and around 5 times more than the somatosensory cortex of a mouse. Similarly, the pyramidal cells of the human prefrontal cortex show around 72% more dendritic spines than the cells of the macaque prefrontal cortex, and approximately 5 times more than titi monkey prefrontal cortex or the mouse motor cortex. These data indicate that the pyramidal cells of the human cerebral cortex can integrate many more afferences than those from any other species studied, and that there are significant differences between the cortical areas, and between species.
In addition, the number of symmetric (inhibiting) and asymmetric (exciting) synapses per neuron have been observed using electronic microscopy, and this number in humans is much higher than in mice and rats, which means a much higher complexity in the exciting and inhibiting circuits. Also, significant differences between species have been noted when it comes to proportion and types of GABAergic interneurons (inhibiting). One of the most important examples is the existence of a special type of GABAergic interneuron named double bouquet cells. These cells were discovered by Cajal in the human cerebral cortex, and are characterized by long axon collaterals - which produce vertical beams densely grouped (like a horse tail)- and due to being very numerous and producing a microcolumnar structure with a very regular distribution. Considering that each horse tail establishes hundreds of inhibiting synapses with dendritic spines and arbors within the narrow field of vertical distribution of the axonal branches, it is believed that double bouquet cells represent a key element for the microcolumnar organization of the neocortex. Nevertheless, this microcolumnar organization has only been observed in man and other primates, but never in rodents (rats and mice), lagomorphs (rabbits), artiodactyles (goats) and carnivores (cat, lion, dog), which suggests there are fundamental differences in the organization of the cerebral cortex between species.
To conclude, it is probable that as new, detailed human cortex microanatomical studies are published, further differences between humans and other species will be discovered. Of course, we do not know what is the exact meaning of these structural variations when it comes to correlating them with human and other animal species characters, but we believe that these observations take us one step further into tackling the passionate topic of studying the neural substrate that makes us humans.
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.
2. The success of the brain
2.1 Genes and brain
All living beings are thermodynamically improbable entities that can only overcome the universal flux towards disorder and entropy through the exploitation of the information fluxes of our universe, thus, by accumulating and using information. Craniate animals have two powerful processors within us: the genome and the brain. The genome is housed within the nucleus of our cells, in chromosomes. The brain is housed in our skull, like a treasure protected in a safe box. We have millions of genome samples, but a single brain. The genome saves information in DNA sequences. The brain saves information in neuron connection patterns. The genome is a safe processor, although an extremely slow one. The brain processes much faster, being able to answer in real time to the challenges posed by a changing environment. The fundamental processor is the genome, as it is the genome who invented the brain, and not the other way around.
The brain is a system more complex than the genome by several degrees of freedom, which is the reason why it is much more difficult to understand. Until now we have been more successful in the exploration of the genome than in the exploration of the brain; we have managed to understand better the fundamental mechanisms of the genome than the brain. Nevertheless, the discovery and functional understanding of each of the genes involved in the development of the brains, and the biochemical circumstances of their activation and deactivation, will offer us new paths for the study of cerebral mechanisms and systems. In any case, the success in the discovery of the genome is the success in the discovery of the brain, a key milestone in the tortuous path toward self-understanding.
2.2 The place of culture
Human nature, our natura, is written inside our genome like culture is written inside our brain. Nature remains static throughout our life, our genes do not change. We die with the same genes with which we were born, and the same with which we were conceived a the time of fecundation (by the fusion of half genome from our mother and half genome from our father to give shape to an entirely complete and novel individual genome). Culture is dynamic, changing continuously. Each day we learn and forget things. Our natura is passed genetically, while culture is transmitted by social learning. Our natura, our genome, comes from our predecessors, while our culture can come from different individuals other than our predecessors. The fundamental study of cultural dynamics is awaiting a better understanding of the brain's functional plasticity: how is cultural information codified, how is it added, how it is erased, and how is it changed.
The cultural phenomenon exists in many species of animals. We have been witnessing a formidable explosion of human culture in the last five thousand years, withstood by the introduction of artificial support mediums and extra-cerebral cultural information. The invention of writing allowed us to register data, memories, and fantasies outside of our head, over a brick of clay or over a sheet of pressed papyrus. This way, we began to have cultural contents outside of our brain. The invention of the printing press only accelerated this phenomenon. The entire Espasa Encyclopedia has never been inside a brain, it has only existed in the 90 thick volumes of paper it is made of. New support mediums like vinyl gramophone records, photographic plates, and magnetic tapes have further broaden this process. In the last decades, the combination of computers and the Internet with its multiple servers, together with the rest of current IT paraphernalia, have created a huge space where not only cultural contents are saved, but they are also processed and modified. This is what we cal web-2, which has certain structural similarities with a "superbrain", whose neurons would be each of us. This is only a metaphor, but still shows us the success of the incredible potential of a real brain, the one we have inside our skulls.