Abstract
In the ontogenesis process, the cerebral cortex undergoes age-related changes. So far as, unlike practically all other systems of mammalian organs, the brain continues to develop and receive new functionality in the postnatal period. Thus with age, there are changes in the bioelectric characteristics of the neocortex. The purpose of the research is to determine the age and sex changes in the bioelectric activity of the cerebral visual cortex of male and female rats of different ages. In the article, we examined changes in absolute (μV2) and normalized (%) indicators of electrical activity of the visual area of rats of different sexes in four age groups: juvenile, young, mature, and presenile age. The research was carried out by the method of registration of bioelectric activity of electrocorticograms (ECoG). Results of multifactorial dispersion analysis of absolute and normalized ECoG indicators of the visual area of the cerebral cortex of rats of all ages showed that there were reliable changes in the frequency-amplitude characteristics of bioelectric activity related to age. At a young age, males have probably lower absolute and normalized power of the delta-rhythm and the normalized beta-like rhythm rate. There was a tendency of decrease in the theta-rhythm. As a result of this redistribution of rhythms a desynchronization of the electrical activity of young males was observed. Mature males have lower absolute power indicators than younger age groups. According to normalized indicators, a synchronization of rhythms of males in the mature age group was observed, which together with values of absolute power can indicate a decrease of the functional activity level of the neocortex and an increase of the influence of endogenous mechanisms on neuronal activity of the visual area of the cerebral cortex. In the presenile age, there was a desynchronization of rhythms. The indicators of an absolute and normalized power of females in the young age group pointed to the synchronization of the bioecoactivity of the neocortex. Among the low-frequency waves, theta-rhythm rhythm dominated in the females of young age. In the mature and presenile age females, there was a probable increase in the percentage of normalized parameters of high-frequency beta waves. The predominance of this rhythm may indicate an increase of cortical tone. The correlation of values of absolute and normalized indicators of bioelectric activity affirmed the desynchronization of the ECoG rhythms of females of mature and presenile age. Sex differences are expressed by a decrease in the absolute power of all ECoG rhythms of the visual area of the cerebral cortex of females relative to males. The age-related changes occurred in a different way in rats of different sex. At a young age, males had desynchronization of rhythms, and females had synchronization, in the mature age it was vice versa. The age changes of the electric activity of the cerebral visual cortex of rats in our opinion may be largely associated with involutional changes of various neurotransmitter and hormonal systems.
Highlights
The bioelectric activity of the cerebral cortex is one of the indicators of the functional state of the organism insofar as any external or internal factors that influence the body lead to a change in the bioelectric activity of the cerebrum, which in its turn reflects the interaction of excitatory and inhibitory processes of cells of the central nervous system
Biopotentials arise in response to afferent irritation and reflect the continuous activity of the brain, which makes it possible to analyze the presence of age and sex changes of the electrical activity of the visual area of the neocortex
We analyzed the dynamics of the rhythms of background electrical activity of males in different age groups of the visual area of the cerebral cortex in absolute and normalized indicators
Summary
The bioelectric activity of the cerebral cortex is one of the indicators of the functional state of the organism insofar as any external or internal factors that influence the body lead to a change in the bioelectric activity of the cerebrum, which in its turn reflects the interaction of excitatory and inhibitory processes of cells of the central nervous system. The presence of various rhythms in the electroencephalogram (EEG) causes the ability of the slow variations of the electrical activity to repeat rhythmically (Vorob'eva & Koljadko, 2007). The feature of space-time organization of rhythmic components of the electrocorticogram (ECoG), the analysis of background activity of the brain, allow determining the pattern of maturation of cortical structures of the cortex of a particular cortex zone in different age periods. It is well known that activating reticular cortical and limbic cortical systems cause an increase of the level of cerebrum functional activity (Andrzejewski, 2011; Man’kovskiy, 2013). As the final effect of the action of these two systems is realized on the same cerebrum cortical systems, the level of functional activity is determined by the specific weight of the activity of each system in this situation (Meyer, 2014)
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