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Two hemispheres of the brain with different speed and accuracy perform different tasks — this is the laterality. The patterns of our behavior are based on structural laterality: brain regions in different hemispheres vary in size, contain more dendrites, or in principle have different structures. Laterality also manifests itself in the activation of brain areas. If you use a functional MRI to measure blood pressure in the brain while performing a certain task, the pressure in one hemisphere will be higher than in the other.
Types of laterality
There are various forms of laterality, the most common being left — or right - handed. Also naturalnosti — the preference of left or right feet (e.g. which foot to kick the ball), the eye (how the eye to see in the microscope), ear (which ear to lean against the door). Laterality even affects which side we turn to hug or kiss someone, or how we cradle a baby. Emotions, facial recognition, and space perception are also lateral.
There is no scientific evidence that one hemisphere can be generally more developed than the other. Usually the hemispheres of the brain are the same size. Laterality is a division of functions: some tasks are performed by the left hemisphere, others by the right, and this is strictly specific to certain areas of the brain. For example, if you are right-handed, it only means that your left motor cortex is better developed than your right. Not necessarily the left visual cortex and the entire left hemisphere are better developed. Usually for right-handed people, other forms of laterality will also be right-handed, but this is not necessarily true. About 90% of people are right-handed, and this is highly correlated with leg preference: 80% of right — handed people have the leading right leg. Other forms of laterality intersect in 60-80% of cases.
Formation of laterality
Laterality is formed in the early stages of development of the organism. Ultrasound studies of human embryos show that most show a tendency to move the right hand more than the left before birth. If you wait six years and check these same children, it turns out that in 95% of cases, the leading hand is the same as the one they preferred before birth.
Right-or left-handed is determined before we are born. Most likely, this is influenced by a combination of genetic factors and early environmental factors, such as the balance of hormones in utero. Men are more likely to be left-handed than women. 10% of people in the world are left — handed, with 11% of men left — handed and 9% of women left-handed. This suggests that sex hormones may play an important role in the formation of laterality. Recent research suggests that the stress hormone cortisol may also be important: if a mother experiences stress during pregnancy, it affects laterality.
Genes that determine the axial symmetry of our body also affect laterality. The human body is asymmetrical: for example, the heart is on the left, and the liver is on the right. The Nodal genetic signaling cascade determines the position of these organs. Some genes encoding this signaling cascade are responsible for brain asymmetry — for preferred arm or language laterality, such as the PCSK6 gene. There are genes that determine the development of neurons (LLRTM1), and genes that play a role in the development of neurotransmitters, such as glutamate or dopamine. So if we consider the genes underlying laterality, it all comes down to the peculiarities of the formation of symmetry of the body and the development of the brain.
Naturalnosti animals
It used to be thought that only humans could be left-handed or right-handed, but now we know that many animals also have laterality, such as cats, dogs, rats. Laterality is seen not only in mammals. For example, the parrots take the food with their paws, and often one of the legs of the bird will be leading. There are researchers dealing with laterality in toads, fish that have a preference for which side to swim, and even invertebrates. Bees touch the world with antennae, and one antenna the bee can use to determine the type of flowers, the other-for other purposes. Laterality is observed in representatives of the entire animal Kingdom.
People are noticeably lateral because we use our hands to do complex tasks like writing. Most animals do not have such a pronounced preference for a leading limb because they perform more primitive actions: holding food is not writing a novel. We believe that all animals have laterality, but it is not as strong as in humans, and it all depends on what tasks they need to perform in the current habitat.
Emotional naturalnosti
To study emotional laterality in humans, we use MRI: you can put a person in a CT scanner and measure blood pressure in the brain. If the subjects do not perform any tasks, the pressure level is usually symmetrical in both hemispheres, and if you give a specific task, for example, to show a touching video and ask the participants to react in a special way, the activity is noticeably shifted towards one of the hemispheres. For example, if you show a video that causes acute negative emotions, more blood will flow to the areas responsible for emotions in the right hemisphere. In the same way they study language skills, and the perception of faces, and other features of the brain.
The lateralization of emotions in animals is difficult to study because they cannot perform complex tasks, and there are very few scanners designed for animals. But there are studies on behavioral markers of emotional laterality in animals. Italian scientist Giorgio Vallortigara wrote a famous work about how dogs wag their tails. The dog can wag his tail, showing many different emotions: when she sees the owner, the tail wags more to the right side, so more involved in the left hemisphere. Seeing an aggressive opponent, the dog shows negative emotions and wags his tail more to the left-the right hemisphere is activated. This is how behavioral markers of laterality work in animals.
Symmetry and asymmetry of the brain
For complex actions are responsible areas of the higher parts of the brain, and they are usually asymmetric. Simple functions are localized at lower levels, and they are more symmetrical. For example, the centers of the brain responsible for breathing or heartbeat are located clearly symmetrically, the centers of vision too: the occipital cortex, responsible for visual signals, is the same in the right and left hemispheres, because we see the same with both eyes.
The brain consumes about 20% of the body's energy: 20% of your calories go to the brain. So 10% of the energy goes to the left hemisphere and 10% to the right. Laterality is evolutionarily efficient because it conserves energy. Each function of the brain consumes about 1-2% of energy, and for long periods of time it is quite a lot. If you can eat 1-2% fewer calories in a year, you have an evolutionary advantage. Evolution always prefers more efficient systems, and perhaps this is the reason for the lateralization of the brain.
Laterality does not mean that one half of the brain is working while the other is inactive. On the contrary, one hemisphere is working on its task, while the other hemisphere performs its, and the brain is not idle. Of course, the fact that we use only 20% of the potential of our brain is not true. All 100% are involved, otherwise evolution would have got rid of unused parts long ago, because the brain is an organ with an incredibly high energy consumption. Of course, we do not use all areas of the brain at the same time all the time: it would be pointless to excite all the neurons at once, because we never perform all possible types of tasks at once.
What else is unknown about laterality
We know that in many mental illnesses, such as schizophrenia or depression, patients exhibit very unusual, laterality - related patterns of behavior. No one has yet figured out why patients with schizophrenia are more likely to be Ambidextrous than mentally healthy people, and why they have a strange lateralization of speech centers. The study of the causes of this phenomenon can help us to better understand the essence of schizophrenia.
It would be interesting to know how environmental factors affect laterality, because not everything can be explained by genetics. Various environmental factors, such as maternal stress during early embryonic development, seem to play an important role in the formation of laterality, but we do not yet know what signaling cascades are involved. I wonder what a similar naturalnosti animals on naturalnosti person and how it differs, why do some animals it is expressed brighter, and the others less. At the interspecies level, laterality has not yet been explained.
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