What Is Brain Asymmetry?

The corresponding functions of the two regions of the human brain are different. This phenomenon began to appear in infancy, and gradually developed and stabilized with the influence of the environment, especially language learning. In the early stages of life, the functions of the two hemispheres are somewhat plastic. When one side of the hemisphere is damaged, its function can be compensated for by the other side. Impossible.

In 1861, French neurologist P. Broca observed a patient who could understand other people's speech, but did not paralyze the oropharyngeal muscles, but could not speak by himself. An autopsy was performed after the patient's death, and the pathological damage was located in the posterior subfrontal gyrus of the left hemisphere, which was just before and after the cortical representative area controlling the movement of the oropharyngeal muscle, and was named the Broca area. In 1874, the German scholar C. Wernicke found another patient who did not lose the ability to speak actively and had normal hearing but could not understand what others and himself said. The cortical lesion was in the posterior superior temporal gyrus of the left hemisphere. This area was later Named Wernicke. Subsequently, due to continuous research supporting the discovery of Broca and Wernicke, in a fairly long period of time, the academic community generally believed that the left hemisphere of the right-handed brain of the right-hander was the dominant dominant hemisphere, which not only dominated Speech functions, and dominate other cognitive functions, while the right hemisphere is completely subordinate to the left hemisphere and is a "dumb" hemisphere. With the deepening of clinical observation and the development of experimental technology, it is found that the right hemisphere and various non-verbal forms of psychological activities, such as perception and memory of images, perception and positioning of time and space, processing of musical melody and tunes, and color discrimination They are closely related, and have a certain feeling and understanding of language. Since the 1950s, a series of studies by the American neurobiologist RW Sperry and others on the split brain further revealed the asymmetry of the function of the brain's two hemispheres and many special functions of the right hemisphere. Sperry won the Nobel Prize in Medicine and Physiology in 1981 for this.

A closer look at the anatomy of the two hemispheres of the brain reveals that in the temporal plane region of the temporal cortex of the cerebral cortex, there is a significant difference between the two cerebral hemispheres. Some people have analyzed 100 adult brains, of which the temporal plane area of the left brain is larger than the right 65%, the sides are approximately equal 24%, and the left is smaller than the right 11%. This area of the left hemisphere is speech capable, as its damage often leads to severe speech disorders.

The most common method for studying the asymmetry of the function of the two hemispheres of the brain is as follows: Quick test method: let the subject face up to the gaze point on the screen in front of him, and use the quick tester to quickly present a transient stimulus in his left or right field or bilateral field No more than 200 milliseconds). Because the subjects have not had time to generate eye movements, the stimulus presented in one side of the field of vision can only reach the contralateral hemisphere, so that the ability to recognize the side hemisphere can be checked. The response time or error ratio of the subjects was used as an indicator to estimate the superiority of one side of the hemisphere. Most of the materials on the asymmetry of the brain's two hemispheres are obtained from the tachymetry method. Binaural listening test: Although hearing is not the same as vision, the information transmitted from one side of the field of vision is completely transmitted to the contralateral hemisphere through the visual cross, but the projection of auditory information from one ear to the ipsilateral hemisphere is much weaker than to the contralateral Hemisphere projection. Put the two earphones on the two ears of the subject separately, so that both ears can receive different auditory stimuli at the same time, and the subjects should say everything they heard. When the stimulus is given as a number, most right-handed people report more accurately on the right ear than on the left ear. When the stimulus is changed to music, the result is the opposite. This reflects the asymmetry of hemisphere function on both sides of the brain. One-sided cerebral palsy method: Inject isoprene barbital in the left or right carotid artery to selectively numb the left or right hemisphere, and observe the nature and duration of speech dysfunction. This method is widely used in the diagnosis of verbal dominant hemispheres before brain surgery. Clinical observations and controlled tests on patients with split brains: Patients with split brains refer to patients who have severed their carcasses due to severe seizures. The corpus callosum is a huge bundle of fibers that connects the two hemispheres of the brain. The two hemispheres lose contact after being severed. It is therefore relatively easy to separately present visual, auditory and tactile stimuli to the left or right hemisphere. Most of the important information about the asymmetry of the cerebral hemisphere function is derived from observations and tests of this kind of patients. According to the research of the different methods mentioned above, it is generally believed that the majority of the right-handed person's left hemisphere has the advantages in speech, order, time, rhythm, and logical analysis of propositions; the right-hemisphere has advantages in nonverbal, overall shapes And the perception of space; in addition, the left and right hemispheres also seem to differ in their emotional responses. The response in the right hemisphere was stronger or less optimistic.

Human facial expressions are also left-right asymmetrical. Some people have experimented: cut photos of actors performing various expressions of joy, anger, sorrow, and fear, cut in half from the center line of the face, and then print the two halves of the opposite side. The photos are stitched into a face photo with the left and right sides of the original left and right sides. Mix the two stitched photos together, and ask the participants to pick out photos they think have more expressiveness. As a result, there were many more photos selected from the left face. This result is also consistent with the knowledge of anatomy. The left face, especially the lower part, receives nerve fibers projected from the right brain. It appears that the right brain plays more of a role in facial expressions. ^[1]