The concept of functional hemispheric asymmetry ( FMA ) arose after \ found that the symmetrical formations of the right and left hemispheres play a different role in the brain. This primarily refers to the higher cortical functions – speech, gnosis, praxis. FMA is also manifested in the organization of sensory and motor functions. Due to the fact that the speech, as well as the representation of the leading hand in right-handed people is most associated with the left hemisphere, this hemisphere is called dominant, and the right hemisphere is subdominant. There are ideas that the true hemisphere is dominant in true left-handers, although in left-handers the lateralization of functions is more variable and, in general, hemispheric asymmetry is less pronounced . A significant contribution to the study of functional inequality of the hemispheres was made by the work that showed that in patients with a section of the corpus callosum, the right and left hemispheres perform various specialized operations.
The fundamental works mentioned above were carried out by neuropsychologists and clinicians on the brain with damage to certain formations. Laterality was manifested in the form of stable conservative features associated with the structural and functional characteristics of the organization of the right and left hemispheres. For a long time it was believed that stationary asymmetry is the only form of FMA, especially since there is a fairly stable predominance of certain motor and sensory characteristics (“leading hand”, “leading eye”, “leading ear”, etc.).
However, there is another asymmetry in the brain activity, the information about which is reported by studies performed using biochemical mapping, as well as
registration of electroencephalogram and induced electrical activity, local cerebral blood flow, etc. This asymmetry is dynamic and depends on the functional state of the brain, which determines the selective increase in activity in the right or left hemisphere. For example, the prevalence of the spectral power of the alpha rhythm in the right hemisphere is statistically significant in the state of quiet wakefulness with eyes closed. But on the EEG recording it is possible to distinguish areas where there is no such predominance. Another example is the alternate shear activity in the right and left hemispheres of dolphins, when a qualitatively different EEG is recorded in both hemispheres of the brain .