The functional asymmetry of the activity of the hemispheres depends mainly on three factors: the asymmetry of the external environment, the nature of interhemispheric relations and the specific features of the work of each hemisphere. The notion that the asymmetry of the external environment forms the asymmetry of the brain activity and, accordingly, the asymmetry of behavioral reactions, is in full accordance with modern data on the morpho-functional organization of the brain. These views found experimental confirmation in the works , as well as in our research.Interhemispheric relationships are largely determined by the effects that are transmitted via transcallosal connections. It follows from past works and modern studies that the nature of these influences is predominantly inhibitory, although transcollosal connections may be exciting. Braking neurons that transkalozalnuyu transfer, mainly GABA-ergic Hemispheric relations can be seen in the following example. If the activity of one of the hemispheres is somewhat higher, then in this case the activity of the other hemisphere will be inhibited, and the level of inhibitory influences going to the first hemisphere will also decrease. This happens until such time as the processes start to develop in the opposite direction under the influence of any effects leading to a decrease in the activity of the first hemisphere.The behavior of such a system manifests itself in the form of a variable predominance of the activity of the right or left hemisphere, and the state of the same activity of both hemispheres will be unstable. The alternation of the activities of the right and left hemispheres allows more economical use of energy reserves .
A vivid example of such activity is the alternation of the phases of sleep and wakefulness in the right and left hemispheres of dolphins.
Here it is convenient to introduce the concept of dynamic functional asymmetry, by which we mean unstable differences in the activity of symmetrical brain formations, manifested in their unequal activity. Dynamic PMA can be assessed using electrophysiological, biochemical, behavioral, and other indicators. Dynamic functional asymmetry depends on the functional state and often manifests itself in a statistically significant predominance of activity in one of the hemispheres.