In this blog post, we explore whether the connectome—the network of neural connections within the brain—can help unlock the secrets of the human mind, memory, and personality.
Ever since humanity became aware of the existence of the mind, we have ceaselessly sought to understand it. This quest evolved into the academic discipline of philosophy of mind (or philosophy of the mind), which has examined the relationship between mental phenomena and the physical body. A central question in this inquiry is whether the body and mind are one or separate entities. Descartes, for instance, advocated for mind-body dualism, arguing that humans are beings in which the physical body and the mind coexist as distinct entities. Although he lost some persuasiveness by offering a somewhat vague answer—that the two substances interact at a place called the pineal gland—to the question, “How, then, can the dissimilar body and mind interact?” his work is significant in that it marked the beginning of a serious, systematic discussion of the human mind, a topic debated since ancient times.
Subsequently, scientific advancements revealed that the brain serves as the central hub for both human physical and mental activities. Subsequently, the goal of brain researchers became to understand the nervous system as a whole, including the brain, and to identify the factors influencing mental activity within the brain. Early theories were influenced by phrenology, a discipline that sought to infer human personality and psychological traits from the shape of the skull. At the time, phrenology advocated a parallel theory, claiming that analyzing the skull could reveal the structure of the cerebral cortex. Based on this theory, scholars studying the brain at the time argued that brain size influenced human mental activity. They even produced experimental results suggesting a relationship between brain size and intelligence; however, this was merely a “correlation” and did not prove that people with larger brains necessarily possessed greater intelligence. Subsequently, scholars recognized the limitations of phrenology and shifted their focus from the brain’s overall size to its localization, proposing the hypothesis that specific regions of the brain perform distinct functions. Several events influenced the development of this hypothesis. One such incident involved a construction worker who survived after a rebar pierced his skull but whose personality changed so drastically that he became a completely different person. Additionally, research supporting this hypothesis included the discovery of “Broca’s area” by the French surgeon Paul Broca, who studied a patient who could not speak fluently but had normal language comprehension and speech production mechanisms, and the discovery of “Wernicke’s area” by Carl Wernicke, who treated a patient who could form words but could not combine them to create context. However, there are cases where the value of such research is somewhat underestimated. One such example is the recovery of a child who underwent surgery to remove one of the brain’s two hemispheres. Children who suffer from frequent epileptic seizures severe enough to cause extreme physical and mental weakness often undergo such extreme neurosurgical procedures. Although one might expect them to be completely unable to move the side of the body opposite the resected hemisphere, these children are not only able to walk but may even be able to run. Their intellectual abilities are largely unaffected; in fact, with the seizures cured, they sometimes exhibit even higher intellectual capabilities. This demonstrates that functional reorganization can occur within the brain, and a new challenge has emerged: rather than studying the functions of specific brain regions, we must explain how those functions are generated and how functional reorganization can take place.
The theory proposed to solve this new challenge facing brain researchers is “connectomics.” A connectome is a comprehensive map of the connections between neurons—the nerve cells in the brain—and can be viewed as a kind of circuit diagram. Researchers in connectomics explain that all human experiences and traits are recorded in these neural connections and expressed through them; they suggest that by studying the human brain’s connectome, we can uncover how memory, personality, and talents are stored and utilized in the brain. Let’s look at an example to understand connectomics. The ability to ride a bicycle can be viewed as developing when the neurons responsible for the muscles involved in cycling and those involved in balance connect, based on the experiences and memories we gain while learning to ride. In other words, neurons form connections and strengthen them; if we don’t ride a bicycle frequently, these connections weaken and may even be reorganized. In short, connectomics is a field of study that explains human physical and mental activities through the connection, strengthening, and reorganization of neurons. As connectomics advances in the future, understanding the process of neuronal connections could help foster intelligence, and reorganization could be utilized in patients’ rehabilitation processes.
