The human brain, with its approximately 80 billion neurons, is one of the most complex systems in the known universe. Although its appearance might suggest modesty—weighing less than two kilograms, being composed of about 60% fat, or constantly floating within the skull—this organ holds as many mysteries as undiscovered galaxies. The brain not only keeps us alive but is also responsible for connecting the body to something far more abstract, something that could be physical or spiritual, something that guides the individual from birth to death: the mind.

Since the discovery of neurons at the end of the 19th century, a milestone that earned the Spaniard Santiago Ramón y Cajal a Nobel Prize, neuroscience has emerged as an independent field of research, having previously been a branch of medicine. During this time, especially in recent decades, neuroscience has advanced by leaps and bounds in its quest for answers about the human mind. On the one hand, thanks to neuroimaging techniques like functional magnetic resonance imaging (fMRI), we are now able to map "where" cognitive processes occur in the brain. For example, they answer questions like "where in the body is tobacco addiction located?" On the other hand, tools like electroencephalography (EEG) help unravel "when" these processes occur, as they measure electrical activity in real time and record the activity patterns that occur every millisecond. In some cases, we are even able to understand "what" the mind does through molecular neurobiology, which identifies the physicochemical mechanisms involved in thought.

However, despite these impressive advances, and without diminishing their merit, we are still far from understanding "how" and "why." We have no idea how neural networks and their interactions produce phenomena like memory or consciousness. We also don't understand why certain cognitive processes occur the way they do, nor what underlying principles govern these functions. Similarly, Matteo Carandini, a scientist at University College London, points out that "most researchers agree that, except in very specific cases, the relationship between neural circuits and human behavior is completely unknown."

How to Decode the Mind

However, being cautious about the findings doesn't mean being disappointed with them, and undoubtedly, perseverance is yielding clues to progress. British neuroscientist David Marr, one of the great minds of the 20th century, maintained that, to continue advancing our understanding of brain processes, efforts are required on three complementary levels: first, the functional properties of each process must be defined, such as what exactly vision is, how memory works, or how decisions are made. Second, the algorithm that each cognitive process performs must be identified and broken down into specific steps. In the case of vision, this could refer to how the brain converts the light signals reaching the retina into a coherent image. The third and final level focuses on determining how neurons and their connections execute these algorithms. In other words, how do the physical and chemical properties of neurons carry out the algorithms described in the second level? This is the most detailed and biologically grounded level, investigating the structure and function of the biological hardware.

Fortunately, the 21st century has brought a series of extraordinary discoveries that worthily continue the legacy of Marr and all his predecessors. The study of the hippocampus, for example, is allowing scientists to directly observe how memories are formed and manipulated. This is possible through optogenetics, an innovative technique that combines optics and genetics to control cell activity. Using pulses of light, neurons can be activated or deactivated, and the resulting changes in behavior can be observed. Currently, optogenetics is practiced only in animals, but it has proven very useful for understanding how memory works. For example, specific networks of neurons have been found to be responsible for forming memory associations. Specifically, synapses in the amygdala and basal ganglia may be involved in conditioning, the type of learning that Pavlov demonstrated with his famous dog and the bell.

But what if what we are learning about the rodent brain, the workhorse of modern neuroscience, cannot be applied to humans? This seems unlikely given the similarities between the neuroanatomy of both species. Therefore, although they are not identical organs, what is learned from one can be applied to the study of the other.

Artificial intelligence to decipher the human mind

In any case, the exploration of the human mind goes far beyond animal experiments, as it draws on its interdisciplinary nature and integrates knowledge from many other areas, such as psychology, linguistics, and engineering. In a recent study, researchers at the University of Texas have demonstrated the usefulness of combining artificial intelligence (AI) with neuroscience to decode what happens in the human mind. Thanks to the combination of data collected through fMRI and AI-powered language models, they were able to recreate several stories that a person heard (or made up) while inside the scanner. This system is far from perfect, as it only manages to provide a general idea of ​​what the person is hearing or thinking. However, this represents a huge step toward understanding how the mind processes language. In the future, we can expect to see more advanced applications of this technology, even at a commercial level, which could revolutionize areas such as communication, education, and the treatment of neurological disorders.

Although neuroscience has not yet found many practical applications for these models, it is gradually incorporating this knowledge to continue studying the human brain. Neuroscientist Nikolaus Kriegeskorte, from Columbia University, points out that "contemporary AI models, despite being simpler compared to real neurons, can perform cognitive tasks." For example, "AI allows us to conduct experiments that simulate brain injuries and explore cognitive functions in ways that are not possible with living brains."

Much more than curiosity

On the other hand, the fact that there aren't many practical applications yet doesn't mean they don't exist, and certainly not that the progress achieved in the last 100 years has been a mere whim to satisfy existential curiosity. In reality, the study of the mind through neuroscience and other disciplines greatly contributes to the development of treatments and interventions for psychological and psychiatric disorders. Neuroimaging techniques have improved the diagnosis and monitoring of neurodegenerative diseases, while the study of neuroplasticity is enabling the creation of rehabilitation programs for patients with certain injuries. Likewise, neuroscience fosters ethical debates such as those surrounding brain-computer interfaces, mind-reading technology, and the limits of cognitive enhancement.

The mind has been the subject of study since the earliest civilizations, always approached with the prudence and respect due to something that could be the bridge to realities that transcend the material. Now, and since the generation of Ramón y Cajal, the mind is finding its raison d'être in the brain, an organ that offers physical explanations for human intelligence, thanks to neuroscience. Many other fields also offer their perspective to study it better, clinging to the ideal of unraveling once and for all the true power of 80 billion neurons contained in a kilo and a half of floating mass.

The original article was published in Spanish at Ethic.es