It is well known that sensory stimulation increases the intensity of energy metabolism in the nerve centers involved in the transmission and processing of information rmatsii . During photostimulation, there is a two-wave increase in blood flow in the visual region of the cortex, with the first wave occurring within 5 to 7 seconds from the start of stimulation due to an increase in extracellular potassium concentration, the second wave develops after 10 to 15 seconds under the influence of a decrease in the pH of nerve tissue . Acidification during the second wave occurs as a result of increased energy metabolism and the accumulation of carbon dioxide, as well as lactate. An increase in the concentration of hydrogen ions contributes to a prolonged increase in blood flow. At the first stage, despite an increase in energy metabolism, the pH can shift to the alkaline side, which is associated with the active leaching of carbon dioxide as a result of increased blood flow . Therefore, the dynamics of pH in the brain during sensory stimulation is determined by two components: changes in energy metabolism and factors regulating the constancy of the CRR.
Sensory stimulation is accompanied by small shifts in SCP. In humans, during a 5-minute photostimulation during registration from the surface of the head, in some cases, a positive shift in the soft-starter AMP is detected. Sound stimulation for 20 min with an intensity of 90 dB caused multidirectional changes in the SCP with a magnitude of several millivolts. Dynamics of OSS could be different polarity, and the statistical analysis revealed significant shifts SCP not been . The multidirectional nature of changes in SCP seems to reflect the result of two processes: increased energy metabolism, acidifying the brain, and cerebral blood flow, leaching acidic metabolic products. Depending on the predominance of a particular process, either a positive or a negative shift in SCP occurs.
The direction of the SCP changes has a certain regularity, namely: the shift of the SCP is determined to a large extent by its initial level. According to our data, changes in SCP during sound stimulation recorded from the surface of the head in healthy subjects are associated with a negative correlation with the initial values of the potential. Consider the proposed mechanism of this dependence. A high level of cerebral energy exchange and a decrease in pH occur with high activity of nerve cells, leading to the accumulation of extracellular potassium. At initially high values of SCP, i.e. with high acidification of the brain tissue and, apparently, with an increased concentration of extracellular potassium, a slight increase in energy transfer during exercise, accompanied by the additional formation of protons and potassium ions in the extracellular medium, causes an increase in cerebral blood flow, which leaches carbon dioxide. This leads to a decrease in SCP and normalization of the CRR. And vice versa, at low initial values of SCP, i.e. relatively low concentrations of protons and extracellular potassium, an increase in cerebral blood flow during exercise is insufficient to wash out excess CO 2 . Therefore, hydrogen ions accumulate in the tissues, leading to acidification of the brain tissue and a decrease in pH. Since such regulation of the cerebral pH level manifests itself under various influences, it is possible that it is universal in nature, so that, in principle, the regulation of the CRR does not depend on the type of exposure, but is determined only by the enhancement (weakening) of energy metabolism and the initial level of CRR.
The nature of changes in SCP during sensory stimulation in conditions of abduction directly from the brain differs from the dynamics of SCP in abduction from the surface of the head. As a rule, these shifts do not exceed 1–2 mV, and the membrane potentials of nerve and glial cells are the most probable source of their occurrence. The maximum changes in both SCP and biochemical parameters develop in the projection zone of the corresponding analyzer.
During visual and acoustic stimulation in rabbits, a negative shift in SCP to I mV was observed in the parietal cortex, associated with the depolarization of neurons. In parallel to this shift, the concentration of extracellular potassium increases, which plays a trigger role in enhancing cerebral blood flow. A correlation was also found between changes in SCP with an increase in the degree of oxidation of respiratory mitochondrial enzymes — NADH and cytochromes . The potential shift during acoustic stimulation is limited by the auditory cortex and is generated by neurons of the upper third of the cortex. Electrodermal stimulation caused a long positive wave in the brain of rats with an amplitude of 3-4 mV. A positive bias was preceded by a relatively small negative deviation of SCP. The most pronounced changes were noted in the frontal and parietal cortex .
Electrical stimulation of the thalamus led to a negative shift in SCP . The dependence of the dynamics of SCP on the strength of the stimulus is shown: weak irritation of the external cranked body was accompanied by a negative, and strong – a positive shift of the SCP . With electrical stimulation of nonspecific thalamic nuclei, the greatest shifts in SCP were observed in the anterior regions of the cortex, and with stimulation of specific nuclei in the corresponding projection zones . During rhythmic electrical stimulation of the cortex of the cerebral hemispheres of dogs, a gradually growing negative shift in the potential of the cortex and a series of slow waves and aftereffect discharges were recorded. The amplitude of the negative shear reached 1.5–2 mV .
Shifts in SCP during afferent stimulation are associated with a negative correlation with the initial level of potential. This pattern is of a similar nature when the SCP was withdrawn both from the surface of the head and from the brain , it was found that with electrical stimulation of specific and nonspecific thalamic nuclei, a slow negative wave arises in the cortex, which changes its sign with surface negative polarization and amplifies with surface positive. Inversion of the SCP shift is also observed if, instead of polarization, strychnization of the cortex is applied, which causes a negative displacement of the cortical constant potential.
So, with sensory stimulation, activation of the projection zones of the cortex is accompanied by a depolarization shift of the membrane potentials of neurons and a slight negative shift in the constant potentials removed from the surface of the cortex. At the same time, a slight increase in energy metabolism and local blood flow is observed in the brain. Changes in the CRR and, accordingly, AMR removed from the surface of the head are generally small and are determined by the resulting two processes: accumulation of CO 2 and lactate during intensification of energy metabolism and leaching of CO 2 as a result of increased blood flow. In cases where an excess of CO 2 and lactate accumulates in the brain, a pH shift towards acidification occurs; when these metabolic products are washed away by 98 enhanced cerebral blood flow, the pH shifts to the alkaline side.
Shifts in SCP during sensory stimulation are causally related to its initial level. There is an aspiration of the system that regulates the SCP of the cortex to reach a certain value at which the action of disturbing factors would be minimal. This suggests that a small disturbing effect can activate the system of regulation of cerebral CRR by negative feedback mechanisms, which leads to its normalization