Every year, in mid-December, a banquet is held in Stockholm for the members of the committee that awards the Nobel prizes and its laureates. The one in 2000 was somewhat special, given that the first prizes of the 21st century were being celebrated. All eyes were on what trends the Nobel prizes would set at the end of the millennium. The Nobel Prize in Medicine and Physiology was awarded to Arvid Carlsson, Paul Greengard and Eric Kandel for their work on the brain, specifically for having discovered how neurons communicate using neurotransmitters. This was the debut of what is said to be the "century of neuroscience".
In these last decades the emergence of neuroscience applied to the study of the human brain has taken place, not only in terms of its structure, genetics, epigenetics, biochemistry and functioning, but also in relation to how a limited physical structure is capable of generating complex behaviours adaptable to countless situations and apparently unlimited ethereal thoughts. This has been reflected in several very ambitious projects, such as the Human Connectome Project, the Human Brain Project and the Big Neuron Project, among others. However, in spite of all these projects and advances, or rather, because of the data we are being given, the brain still hides many enigmas waiting to be solved. It is possibly the most complex object in the known universe. Here are ten of the most prominent mysteries that the brain still hides.
What is conscience?
Consciousness is the state of mind that allows us to realize the things that happen around and within us. All animals with brains have a certain degree of consciousness. It is known that it arises from the dynamic interaction of many neural networks, such as those involved in the senses, memory or emotions, and that there are three areas of the brain that are essential to it: the brain stem, which is responsible for keeping the brain active; the thalamus, which is the center of attention and marks the threshold between conscious and preconscious experiences; and two areas of the cerebral cortex involved in anticipation and planning. However, it is not yet known how the dynamic interaction of these areas allows us to be aware of our environment in order to relate to it in a self-directed way.
How do we decide which experiences we make conscious, and which remain preconscious?
We are constantly receiving data from outside, through the sense organs, and also information from inside our body. However, most of it goes unnoticed, we are not aware of what is going on. The brain has managed the data and on many occasions has generated responses, such as when we walk and avoid an obstacle that we are not aware of having seen. How do we determine which experiences become conscious and which remain in the preconscious? It is known that the thalamus establishes the threshold of consciousness and that emotional aspects play a prominent role, but it is not yet known what the precise formula is that makes the thalamus "decide" to make us participate in a situation.
How can we have a unified perception of reality?
All perceptions that reach us through the sense organs, of very diverse nature and content, are combined with our thoughts. Moreover, sense organs are made up of thousands of receptor cells, each sending its own message to the brain. At any given moment, however, we do not have a cluster of experiences that overlap chaotically, but rather all sensory inputs and thoughts are unified into a single phenomenological experience, which in cognitive neuroscience is called a qualia. And that's the mystery. How do all electrical impulses quickly combine to translate into subjective impressions such as taste, color, or pain? And how does the brain integrate everything harmoniously and dynamically into a unified but subjective perception of reality?
Why can we be aware of our conscience?
Self-awareness is the cognitive process that allows us to be aware of our awareness, which enables us to interpret the world in a reflective way. Interestingly, it is the one mental characteristic that we never lose. Many cases have been studied of people who, due to trauma, a vascular accident, a surgical operation or a neurodegenerative disease, have suffered the loss of some cognitive characteristics, depending on the area of the brain affected. However, no case has ever been found in which a person has lost the ability to perceive himself as an individual subject differentiated from the rest. There are several brain areas involved, all necessary but none sufficient in themselves, so this faculty lies in the dynamic, transient and fluctuating connections that are established. And this is exactly where the mystery lies. If activity is dynamic, fluctuating and transient, and therefore apparently labile, why do we never stop being aware of our own existence?
What does the brain do when we are resting or when we are distracted?
When the brain is at rest, that is, when we are resting or when we are distracted, it tends to decrease activity and takes advantage of the time to regenerate itself: it eliminates waste substances or remakes neural connections, among other things. However, the regions involved in self-awareness keep the activity intact or even seem to increase it, which makes that, proportionally, when we are at rest these areas are much more active than the rest. This is called the "default operating network". In other words, to know who we are it is better to sit quietly for a while than to look in the mirror. Why do these states of relaxation and rest, such as those that provide distraction or meditation, reaffirm the perception of "I"?
Why can't we know reality as it is?
There are many experiments that show that we always perceive reality in a subjective way. One of the most classic is the so-called rubber hand experiment. By means of a mirror game, a person is made to believe that a rubber hand located after the reflection of his arm is really his hand. If the rubber hand is then pricked, the subject feels a puncture that he has never received. In other words, the way we experience reality is not only based on what the senses transmit but also on the expectations we have, and is greatly influenced by previous experiences and even by beliefs. That's why everyone perceives the same situation in a slightly different way. Why doesn't the brain allow us to know reality as it is?
To what extent do genetics condition our behavior?
Of the 20,300 genes that make up the human genome, there are about 8,000 that at one time or another operate within the brain. All of them can have several variants, which influence the way this organ is built and functions. This means that, on the rebound, they influence all aspects of our temperament and the behaviours we manifest. The influence of genes is quantified in percentage and is called heritability. For example, resilience has a 52% heritability. The rest - up to 100% - depends on the experiences lived, the education received and each particular environmental situation. Now, in any aspect of temperament or behavior that we analyze, many genes are involved, which also interact with the environment. The precise way in which all these gene variants interact among themselves and with the environment is extraordinarily complex and, for the most part, still unknown.
How do epigenetic changes affect our children's brains?
Genes adjust their functioning according to the environment where each person grows and lives in. One of the ways they do this is through epigenetic modifications, which consist of adding certain molecules to the genetic material that, without changing the message it contains, alter its functioning. However, it has been seen that some experiences that parents have, such as having suffered a very traumatic experience or having consumed drugs during adolescence and youth, can condition the epigenetic modifications that their descendants will have, through the eggs and sperm that will form them. And this can end up affecting their behaviour, normally increasing the probability of them suffering from mental disorders. How do you decide which experiences will end up altering the functioning of the brain of the unborn descendants? And why do these changes often seem to harm the cognitive functions of children?
How does the brain compute all the data it manages?
Alan Turing, considered the father of modern computing, proposed that the way computers work to compute real-world data should be equivalent to the way the human brain does. However, all attempts to find equivalents have failed. The main difference is that today's computers have a fixed and stable set of circuits, while the human brain is extraordinarily flexible. On the one hand, because it weaves new neural connections from every experience we have. On the other hand, because each thought can follow several parallel paths within the brain, in a way similar to what is proposed by quantum physics in terms of the position and state of subatomic particles. How do these different neural paths end up harmonizing into a single final thought? Or does it happen, perhaps, that only one of the many possible paths ends up becoming conscious and the rest fade away?
Is there such a thing as free will?
The brain activity associated with consciousness occurs about 300 thousandths of a second before we become consciously aware of the situation. That's a considerable amount of time, given the speed with which information is processed. In other words, the brain "knows" what we will do before we know it ourselves. Is this data in contradiction with the existence of free will? Who decides how we act in each situation? Does the brain do it "on its own", based on accumulated experience and the sensory information and thoughts of each moment, and then informs us and makes us aware of it, as this data seems to suggest? There is a diversity of opinions among neuroscientists on this subject. Emotional impulse responses seem to occur in this way. However, reflective responses can take many more paths. At what point do the neural networks involved in rational and reflective information processing and decision making act? To what extent do we have free will constrained by the intrinsic functioning of the brain?