One of the most mysterious and not fully understood “phenomena” is the human brain. Many questions revolve around this complex organ: why do we dream, how do emotions influence decision making, which nerve cells are responsible for the perception of light and sound, why do some people like sprats, while others love olives? All these questions concern the brain, because it is the central processor of the human body. For years, scientists have paid special attention to the brains of people who somehow stand out from the crowd (from self-taught geniuses to calculating psychopaths). But there is a category of people whose unusual behavior is associated with their age - teenagers. Many teenagers have a heightened sense of contradiction, an adventurous spirit, and an irresistible desire to find adventure on their ass. Scientists from the University of Pennsylvania decided to take a closer look at the mysterious brains of adolescents and the processes that take place in them. What they managed to find out, we will learn from their report. Go.
Research basis
Any device in technology and an organ in the body have their own architecture that allows them to work effectively. The human cerebral cortex is organized along functional hierarchies ranging from unimodal sensory cortex* and ending with transmodal association cortex*.
Sensory cortex * - part of the cerebral cortex responsible for collecting and processing information received from the senses (eyes, tongue, nose, ears, skin and vestibular apparatus).
The association cortex* is the part of the parietal cortex involved in the implementation of planned movements. When we are going to perform any movement, our brain must know where the body and its parts that will move are located at that second, as well as where the objects of the external environment are located with which the interaction is planned. For example, you want to pick up a cup, and your brain already knows where the hand and the cup itself are located.
This functional hierarchy is due to the anatomy of the pathways white matter*, which coordinate synchronized neural activity and cognition*.
White matter* - if the gray matter consists of neurons, then the white consists of axons covered with myelin, along which impulses are transmitted from the cell body to other cells and organs.
Cognition* (cognition) - a set of processes associated with the acquisition of new knowledge regarding the world around.
The evolution of the cerebral cortex in primates and the development of the human brain are characterized by the targeted expansion and remodeling of transmodal association areas, which are the basis of sensory representation of information and abstract rules for achieving goals.
The process of brain development takes a lot of time, during which there are many processes of improving the brain as a system: myelination*, synaptic pruning* etc.
Myelination* - oligodendrocytes (a type of auxiliary cells of the nervous system) envelop one or another part of the axon, as a result of which one oligodendrocyte contacts several neurons at once. The more active the axon, the stronger its myelination, as this increases its efficiency.
Synaptic pruning* — reducing the number of synapses/neurons to increase the efficiency of the neuro-system, i.e. getting rid of unnecessary connections. In other words, this is the implementation of the principle “not quantity, but quality”.
During the formation of the brain, a functional specification is formed in the transmodal associative cortex, which directly affects the development of higher-order executive functions, such as working memory*, cognitive flexibility* и inhibitory control*.
Working memory* — cognitive system of temporary information storage. This type of memory is activated at the moment of current thought processes and is involved in decision making and in the formation of behavioral responses.
Cognitive Flexibility* - the ability to switch from one thought to another and / or think about several things at one moment.
Inhibitory control* (inhibition response) - an executive function that oversees a person's ability to suppress his impulsive (natural, habitual or dominant) behavioral responses to stimuli in order to implement a more appropriate response to a particular situation (external stimulus).
The study of the structural-functional connections of the brain began quite a long time ago. With the advent of network theory, it became possible to visualize structural-functional relationships in neurobiological systems and divide them into categories. At its core, structural-functional connectivity is the extent to which the distribution of anatomical connections in a region of the brain maintains synchronized neural activity.
It was found that there is a strong relationship between indicators of structural and functional connectivity at different spatio-temporal scales. In other words, more modern methods of study have made it possible to categorize certain areas of the brain according to their functional features associated with the age of the area and its size.
However, scientists say there is currently little evidence of how changes in white matter architecture during human brain development maintain coordinated fluctuations in neuronal activity.
Structural-functional connectivity is the basis for functional communication and occurs when the white matter interregional connectivity profile in a cortical region predicts the strength of interregional functional connectivity. That is, the activity of the white matter will be reflected in the activation of the executive functions of the brain, thereby it will be possible to assess the degree of strength of the structural-functional connection.
To describe the structural-functional relationship, scientists put forward three hypotheses that were tested during the study.
The first hypothesis states that the structural-functional relationship will reflect the functional specialization of the cortical area. That is, the structural-functional connection will be strong in the somatosensory cortex, due to the processes that determine the early development of specialized sensory hierarchies. In contrast, structural-functional connectivity will be low in the transmodal association cortex, where functional communication may be weakened due to genetic and anatomical limitations due to rapid evolutionary expansion.
The second hypothesis is based on long-term activity-dependent myelination during development and states that the development of structural-functional connections will be concentrated in the transmodal association cortex.
The third hypothesis: the structural-functional relationship reflects the functional specialization of the cortical region. Therefore, it can be assumed that a stronger structural-functional connection in the fronto-parietal associative cortex will be involved in specialized calculations necessary for the implementation of executive functions.
Results of the study
To characterize the development of structural-functional interactions in adolescents, the researchers quantified the extent to which structural connections across brain regions support coordinated fluctuations in neural activity.
Using multimodal neuroimaging data from 727 participants aged 8 to 23 years, a probabilistic diffusion tractography was performed and the functional connectivity between each pair of cortical regions was assessed at runtime. tasks n-back*associated with working memory activity.
Task n-back* - a technique for stimulating the activity of certain areas of the brain and testing working memory. The subject is presented with a series of stimuli (visual, auditory, etc.). He must determine and indicate whether this or that stimulus was n positions ago. For example: TLHCHSCCQLCKLHCQTRHKC HR (problem 3-backward, where a certain letter occurred 3 positions earlier).
Functional connectivity at rest reflects spontaneous fluctuations in neural activity. However, during a working memory task, functional connectivity can enhance certain neural connections or populations involved in executive functions.
Image No. 1: measuring the structural-functional connection of the human brain.
The nodes in the structural and functional networks of the brain were identified using a 400-zone cortical parcellization based on functional homogeneity in the MRI data of the study participants. For each study participant, regional connectivity profiles were extracted from each row of the structural or functional connectivity matrix and presented as connectivity strength vectors from one neural network node to all other nodes.
To begin with, the scientists checked whether the spatial distribution of structural-functional relationships coincides with the fundamental properties of cortical organization.
Image #2
It is worth noting that the relationship between regional profiles of structural and functional connectivity varied greatly across the cortex (2A). A stronger connection was observed in the primary sensory and medial prefrontal cortex. But in the lateral, temporal and fronto-parietal areas, the connection was rather weak.
To better understand the relationship between structural-functional connectivity and functional specialization, the "participation" coefficient was calculated, which is a graphical representation of the quantitative definition of connectivity between functionally specialized areas of the brain. Each of the brain regions was assigned to the seven classic functional neural networks. Neuronal knots of the brain with a high coefficient of participation demonstrate different intermodular communication (connection between brain regions) and, therefore, can influence the processes of information transfer between regions, as well as their dynamics. But nodes with low participation rates show more local connections within the brain region itself, rather than across multiple regions. Simply put, if the coefficient is high, different parts of the brain actively interact with each other; if it is low, activity occurs within the area without communication with neighboring ones (2C).
Next, an assessment was made of the relationship between the variability of structural-functional connectivity and the macroscale functional hierarchy. Structural-functional connectivity largely coincides with the main gradient of functional connectivity: unimodal sensory areas show relatively strong structural-functional connectivity, while transmodal regions at the top of the functional hierarchy show weaker connectivity (2D).
It was also found that there is a strong correlation between the structural-functional relationship and the evolutionary expansion of the cortical surface area (2E). Highly conserved sensory areas had relatively strong structural-functional connectivity, while highly extended transmodal areas had weaker connectivity. Such observations fully support the hypothesis that the structural-functional relationship is a reflection of the cortical hierarchy of functional specialization and evolutionary expansion.
Image #3
The scientists once again remind that previous studies have largely focused on the study of structural-functional connectivity in the adult brain. In the same work, the emphasis was placed on the study of the brain, which is still in the process of development, i.e. on the study of the adolescent brain.
It was found that age-related differences in structural-functional connections in the adolescent brain were widely distributed in the lateral temporal, inferior parietal, and prefrontal cortex (3А). Connectivity gains were disproportionately distributed across cortical regions, i.e. were present in a unique subset of functionally separated cortical regions (3V), which was not observed in the adult brain.
The value of age differences in structural and functional relationships strongly correlated with the coefficient of functional participation (3S) and functional gradient (3D).
The spatial distribution of age differences in structural and functional relationships also corresponded to the evolutionary expansion of the cortex. An age-related increase in connectivity was observed in the expanded association cortex, while an age-related decrease in connectivity was observed in the highly conserved sensorimotor cortex (3E).
In the next phase of the study, 294 participants underwent a second brain examination 1.7 years after the first. Thus, it was possible to determine the relationship between age-related changes in structural-functional connectivity and intra-individual changes in development. To do this, an assessment was made of longitudinal changes in the structural-functional connectivity.
Image #4
A significant correspondence was found between the transverse and longitudinal age-related changes in the structural-functional relationship (4А).
To test the relationship of longitudinal changes in the structural-functional connectivity (4B) and longitudinal changes in the coefficient of functional participation (4S) linear regression was used. Longitudinal changes in connectivity were found to correspond to longitudinal changes in the coefficient of functional participation in high-order distributed association areas, including those in the dorsal and medial prefrontal cortex, inferior parietal cortex, and lateral temporal cortex (4D).
Image #5
The scientists then tried to understand the consequences of individual differences in structural-functional relationships for behavior. In particular, whether structural-functional connectivity during task execution with working memory can explain executive performance. Improvement in executive performance has been found to be associated with stronger structural-functional connectivity in the rostrolateral prefrontal cortex, posterior cingulate cortex, and medial occipital cortex (5A).
The totality of the above observations leads to several main conclusions. First, regional changes in structural-functional connectivity are inversely proportional to the complexity of the function for which one or another area of the brain is responsible. A stronger structural-functional relationship has been found in parts of the brain that specialize in processing simple sensory information (such as visual cues). And in the areas of the brain involved in more complex processes (executive function and inhibitory control) there was a lower structural-functional connectivity.
Structural-functional connectivity has also been found to be consistent with the evolutionary brain expansion seen in primates. Comparative studies of the brains of humans, primates, and monkeys have previously shown that sensory areas (such as the visual system) are very conserved among primate species and have not expanded much in recent evolution. But the associative areas of the brain (for example, the prefrontal cortex) have undergone a significant expansion. Perhaps this expansion directly affected the emergence of complex cognitive abilities in humans. It was found that areas of the brain that expanded rapidly during evolution had weaker structural-functional connectivity, while simple sensory areas had stronger ones.
In children and adolescents, the structural-functional connection increases quite actively in the frontal areas of the brain, which are responsible for the function of inhibition (i.e., self-control). Thus, long-term development of structural-functional connectivity in these areas may improve executive function and self-control, a process that continues into adulthood.
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Finale
The human brain has always been and will continue to be one of the greatest mysteries of mankind. This is an incredibly complex mechanism that must perform many functions, control many processes and store huge amounts of information. For many parents, nothing is more mysterious than the brains of their teenage children. Their behavior is sometimes difficult to call logical or constructive, but this is due to the process of their biological development and social formation.
Of course, changes in the structural and functional connections of certain parts of the brain and the influence of hormonal changes can be a scientific justification for the peculiar behavior of young people, but this does not mean that they do not need to be directed. Man is not by nature an asocial being. If someone shuns other people, it is certainly not due to our biological predisposition. Therefore, the active participation of parents in the lives of their children is an extremely important aspect of their development.
It should also be understood that even at the age of three, a child is already a person with his own character, his desires and his own view of the world around him. A parent should not become invisible to his child, letting him float freely, but he should not turn into a reinforced concrete wall that protects him from knowing the world. Somewhere you need to push, somewhere to hold, somewhere to give complete freedom, and somewhere, having shown parental authority, to say a firm “no”, even if the child is not happy with this.
Being a parent is hard, and even harder being a good parent. But being a teenager is not easy either. The body is changing outwardly, the brain is changing, the environment is changing (there was a school, and now the university), the rhythm of life is changing. In our time, life often resembles a formula-1, on which there is no place for slowness. But high speed comes with a lot of risk, so an inexperienced rider can get hurt. The task of a parent is to become a coach of his child, in order to calmly let him go into the world in the future, without fear for his future.
Some parents consider themselves smarter than others, some are ready to implement any advice they hear on the Internet or from a neighbor, and some are simply “violet” for all the subtleties of education. People are different, but just as communication between its departments is important in the human brain, communication between parents and their children plays one of the most important roles in education.
Thanks for watching, stay curious and have a great weekend everyone! 🙂
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Source: habr.com