EEG integrally reflects the level of activation of brain structures. EEG rhythms result from the summation of the EPSP and TPPS neurons. Normally, in a state of calm wakefulness with eyes closed, the alpha rhythm with a frequency of 8-13 / s dominates in most people in the EEG, most pronounced in the occipital parts of the brain and associated with the activity of the visual centers. In the anterior regions of the brain, predominantly in the area of the anterior central gyri, a 14–40 / c beta rhythm is recorded, which is associated with sensory and motor cortical mechanisms. In healthy people, a small amount (less than 15% of the total recording time) and with an amplitude not exceeding the amplitude of the alpha rhythm, shows the slow-wave activity of theta and delta ranges, with a frequency of 4-6 / s and 0.5-3 / with.
At present, Fourier analysis is most often used for quantitative EEG analysis, which allows one to estimate the spectral power, i.e. the contribution of electrical activity of different frequency ranges to the total EEG.
A detailed analysis of EEG changes in various functional states is beyond the scope of this manual. However, in the most general form, the relationship between the functional activity of the brain and the EEG can be characterized as follows: when the brain is activated, the EEG amplitude decreases and its frequency increases, i.e. the relative spectral power of alpha and beta rhythms increases, and the relative power of slow-wave delta activity – and theta ranges are reduced. In contrast, a decrease in the level of activation in norm is accompanied by an increase in the relative spectral power of theta and delta waves during the reduction of the alpha rhythm (LR Zenkov, MA Ronkin, 1991).
It is known that there is a relationship between the functional activity and the energy supply of the brain. Activation of cerebral structures is accompanied by an increase in glucose consumption and an increase in local cerebral blood flow. The extracellular accumulation of hydrogen and potassium ions plays an important role in enhancing blood flow. There is a correlation between the parameters of the spectral power of the EEG and blood flow, as well as between the EEG and the level of glucose consumption. It is shown that during the transition from sleep to wakefulness, an increase in the frequency of dominant activity in the EEG is accompanied by an increase in the intensity of glucose consumption (D. Ingvar, 1997). However, the relationship between the bloodstream and EEG is quite complex, since the EEG dynamics depend, among other things, on which part of the brain the blood flow has changed. For example,activation of inhibitory structures is accompanied by an increase in blood flow in this region of the brain, but in the EEG, slow-wave activity may increase. Changes in cerebral energy metabolism, for their part, affect the EEG rhythms. Thus, the decrease in energy metabolism associated with cerebral circulatory insufficiency at the first stage causes hyperactivation of the brain structures due to impaired reuptake of the excitatory mediator glutamate and depolarization of neurons, and at later stages – inhibition of the functional activity of the brain.associated with insufficiency of cerebral circulation, causes at the first stage hyperactivation of brain structures in connection with impaired reuptake of the excitatory glutamate mediator and depolarization of neurons, and at later stages – inhibition of the functional activity of the brain.associated with insufficiency of cerebral circulation, causes at the first stage hyperactivation of brain structures in connection with impaired reuptake of the excitatory glutamate mediator and depolarization of neurons, and at later stages – inhibition of the functional activity of the brain.
It can be assumed that there is a certain interrelation between the parameters of the EEG and the UPP of the brain, reflecting changes in the AOP and characterizing the intensity of cerebral energy metabolism. With regard to man, such dependence remains little studied. Most of the studies on the relationship between changes in EEG and SCP are performed on animals with SCP registration directly from the brain surface. In this case, membrane potentials of neurons and glia make the main contribution to the generation of SCP. Shifts SCP in such experimental conditions characterize the change in the excitability of neurons. Increased SCP during abduction from the brain is associated with hyperpolarization of the membranes, and a negative shift in SCP with depolarization. In the majority of studies, suppression of EEG activity was observed with an increase in the UPP (hyperpolarization of neuronal membranes)except for slow waves that could escalate. Reduction SCP at the first stage was accompanied by an increase in the frequency and amplitude of the EEG. With a further decrease in SCP in the EEG, the appearance of epileptiform discharges associated with a depolarization shift of the membrane potential of nerve cells is possible. With a significant decrease in SCP, complete EEG suppression occurred, due to significant depolarization of neuronal membranes (H. Caspers, E. Speckmann, 1974; E. Ohno, 1979).