Scientific research in the cerebral hemisphere

The functional asymmetry between the two hemispheres of the brain, or the concentration of different functions of the brain in one hemisphere, is the main feature of human brain structure and cognition, which is physiologically called cerebral hemisphere advantage, or brain advantage for short. In the hands of more than 98% adults, the left hemisphere is responsible for language processing and grammatical expression, such as words, syntax, naming, reading, writing, learning and memory. Spatial skills are related to the right hemisphere, such as perception of three-dimensional shapes, spatial orientation, self-dressing ability, music appreciation and singing. The right hemisphere can also understand some spoken and printed words. It can be considered that the left hemisphere is scientific and the right hemisphere is artistic. The advantage of one side of the cerebral hemisphere exists in adults, children, babies and even some animals. 1863, French surgeon PierreBroca pointed out that the functions of the two hemispheres are different, and the left frontal lobe may be the cortical area that controls speech. In addition to the dominant speech function of the left hemisphere, people think that the two hemispheres are equal in sensory and motor functions. The left hemisphere receives sensory input from the right side of the body and dominates the muscle movement on the right side; The right hemisphere receives sensory input from the left side of the body and dominates the muscle movement of the left side.

In 1950s, sperry, a professor at California Institute of Technology, really established the concept of left and right brain division. After he and his students tried to cut off all the nerve lines connecting the left and right brains of cats and monkeys, these animals still lived normally, and they could train the two hemispheres to accomplish the same task in the opposite way. The results show that the left brain also has the function of the right brain, and the right brain also has the function of the left brain, but the division of labor and emphasis are different. The clinical study of brain dominance began with the experimental observation of schizencephaly. Natural brain injury can lead to brain division. In patients with brain injury, it was observed that left brain injury caused the loss of right brain function, mainly the loss of language function, but it did not affect the right brain function. Similarly, brain injury on the right side leads to the loss of left brain function, and patients can show clothing apraxia, wearing reverse clothes because they can't tell right from left, unable to draw charts, and impaired visual cognition, indicating that the left and right hemispheres are independent or functionally separated. The main source of schizencephaly is epilepsy. In order to prevent the spread between the left and right hemispheres and weaken the intensity of epilepsy, the method of removing the corpus callosum is often used, and the patient becomes schizencephaly after operation. When the picture flashes in the left half of schizencephaly's vision, the patient can't name the object in the picture, because the visual image is projected to the right hemisphere, and the right hemisphere has no speech function, but the patient can show that they perceive the object in some nonverbal forms, such as collecting the same object with their hands. It shows that the patient's right vision is good, and more importantly, the language center is located in the left hemisphere. In normal people, because of the role of the corpus callosum, the functions of the two hemispheres are linked, so no matter which side the object appears in the field of vision, the name of the object can be said in words.

Taking normal people as the experimental object, this paper mainly studies the normal behaviors related to the cognitive neurophysiology of the left and right brains, such as the perceptual experiment of presenting stimuli to the side, to clarify the existence of brain superiority. The experimental results suggest that the more one side of the brain participates in a cognitive activity, the greater the activity it notices in the opposite receptive field, which leads to the increase of sensory asymmetry. Recently, brain imaging techniques, such as regional blood flow map and positron emission tomography, have been used to observe special sensory activities. These techniques can indicate the areas of enhanced neural activity in cognitive process, but it is still unclear what the enhanced neural activity marks. It is feasible to study normal individuals, and the research objects are easy to obtain, and the differences between individuals such as gender, age, cognitive level, family history, handedness, etc. And it is possible to study the degree of hemispheric asymmetry through the quantitative score of left and right brain differences. Structurally, the right hemisphere of the human brain is slightly heavier than the left hemisphere, but the left hemisphere has more gray matter than the right hemisphere; There is obvious asymmetry in the left and right temporal lobes; The asymmetry of temporal lobe is related to the asymmetry of thalamus. The distribution of various neurotransmitters in the left and right hemispheres is also unbalanced.

Functionally speaking, under normal circumstances, the two hemispheres of the brain cooperate with each other, and the information entering either side of the brain will quickly pass through the corpus callosum to the other side, making a unified response. Schizocephalic research shows that the two hemispheres of the brain may have different functions. Language functions are mainly located in the left hemisphere, responsible for language, reading, writing, mathematical operation and logical reasoning. The spatial relationship, emotion, music appreciation and art of the perceptual object are all located in the right hemisphere.

The function of the brain has unilateral advantages, but it is not absolutely separated. In recent years, many studies have found that the right hemisphere also plays an important role in language understanding. When processing sentences with different complexity, the part of the right hemisphere corresponding to the classical language area of the left hemisphere is also activated, but the activation intensity is lower than that of the left hemisphere.

This passage is summed up from Peng Yong's 200 1 year-old Theory of Brain Functional Asymmetry in General Psychology (Revised Edition): the advantage of one side of the brain has a certain relationship with heredity, but it is mainly formed in the acquired life practice. The results of brain injury at the age of 2 ~ 3 are similar, because one side advantage has not been established at that time; 10 ~ 12 years old, if the left hemisphere is injured, a language center can be established in the right hemisphere; Adults, the left language advantage has been established, and the damage of the left hemisphere leads to irreparable language barrier. In addition, the functional recovery of early brain injury is faster than that of late brain injury, because in the early life, the plasticity of the nervous system is great, and at this time the cerebral hemisphere has not been specialized or the specialization is not obvious.

Anatomically, the two hemispheres of the brain are not mirror-symmetrical, which is the basis of functional asymmetry. The posterior surface of the first temporal gyrus, that is, the temporal surface, has the most reliable morphological asymmetry and is the core part of language synthesis. The left temporal surface is larger than the right temporal surface by about 40%. Other asymmetric parts, such as the left fissure of the brain, have low elevation, large posterior frontal parietal lobe and wide posterior occipital lobe. What is the essence of functional asymmetry between the left and right hemispheres? At first, people used verbal-nonverbal or verbal-visual to distinguish the functional separation between the left and right hemispheres. This classification cannot explain some newer data. For example, in some stimuli with spatial characteristics, the recognition of English handwriting is related to the function of the right hemisphere, while the recognition of printed and oriental ideographic characters is related to the left hemisphere. For another example, I feel that those non-verbal stimuli with sequence and time sequence are more dependent on the left hemisphere than on the right hemisphere, while some auditory stimuli, such as the feeling of music melody, are more dependent on the right hemisphere. Therefore, the essential difference between the asymmetry of the two hemispheres is more accurately described as decomposition-synthesis or functional separation of the time diagram. That is to say, the information processed by the decomposition stimuli arranged in chronological order in the left hemisphere is specialized, such as language and grammar skills; The right hemisphere specializes in synthesizing and stimulating information, and continuously forms a unified image, such as the perception of melody and three-dimensional objects. Of course, there are individual differences in functional asymmetry between the left and right hemispheres. For example, in individuals who lack musical literacy, melody perception often depends on the role of the right hemisphere, but in musicians, it includes the role of the left hemisphere, reflecting that musicians can make greater use of the analytical process of the brain. Is the difference between the two hemispheres absolute or relative? In other words, it is not clear whether each hemisphere has the ability to process information specially processed by the other hemisphere. Although both hemispheres have the ability to deal with language stimuli, it does not mean that the processing methods are exactly the same. The left hemisphere can be processed in the analysis mode, while the right hemisphere can be processed in the whole mode. We can only dialectically think that the difference between the two hemispheres is relative rather than absolute, but we lack enough experimental evidence. In addition, we don't know at which level of the nervous system the brain functional asymmetry exists.

Is there functional asymmetry in animal brain? According to traditional ideas, language is considered as the basis of brain functional asymmetry. Animals have no obvious language, so there is no brain functional asymmetry. However, recent studies show that there is functional asymmetry in animal brains, and there is anatomical and functional asymmetry between the left and right hemispheres of primates. For example, the left lateral fissure of chimpanzees is longer than the right lateral fissure, but the difference between them is smaller than that of humans. In the vocal animal canary, the influence of left hemisphere injury on singing is far greater than that of right hemisphere injury. In addition to primates and birds, other animals such as cats, rabbits, rats and mice all have asymmetric brain function effects. Claw preference also exists in monkeys and mice. Different from human hand preference, the number of individuals with left and right interests is basically the same, while among humans, right-handed people are obviously in the majority. These observations challenge the traditional theory that language is the basis of brain functional asymmetry. It can be seen that the elucidation of the neurobiological basis of brain functional asymmetry is only the beginning.