Visual evoked potentials (VEP) reflect the processing of visual information in the brain. With BA, the SGP reveals certain disorders in the visual system. In patients, as a rule, visual acuity does not change, however, complex visual functions are disturbed – visual memory, spatial and facial gnosis. Patients not they recognize friends and relatives; in the later stages of the disease they do not recognize themselves in the mirror, they no longer orientate themselves in space. Such a nature of the disorders is due to the fact that the atrophic process in asthma affects the associative visual areas and the polysynaptic systems of the limbico-reticular complex with the relative preservation of specific visual pathways and primary visual fields. In accordance with this, with BA, the early components of the P1, N1 VIZ (latent period less than 100 ms) are changed slightly. The late components of the VEP (P2, N2, P3, N3), which are related in their origin to the response of the cortex to the impulses received through the polysynaptic systems of the limbic-reticular complex, suffer the most. The latent periods of the late components of the VIZ in BA are increased (G. Harding et al., 1985; VF Fokin et al., 1989). Besides,in some patients, a reduction in the P3 and N3 components is observed, which leads to a simplification of the evoked response. Patients with the absence of these components are more pronounced violations of the spatial and facial gnosis (N.V. Ponomareva et al., 1991), which confirms the idea of the relevance of polyphase and the complexity of the form of VEP with the quality of information processing in the visual system (L.R. Zenkov, PV Melnichuk, 1985).
The analysis of the relationship between the parameters of SCP and SGP was carried out by us in 47 BA patients (mean age 61.9 + 1.0 years). Registration SGP – bipolar. Univariate analysis of variance showed that in patients with a simplified evoked response (absence of component N3 of the SGP), the SCP in the occipital region was significantly higher (Oz = 21.6 + 4.9 mV) than in patients with the intact component of the SGP (Oz = 11 , 9 + 1.7 mV). Such changes in the VEP are observed at the stage of severe dementia (2b) significantly more often than at the initial stages of asthma. (N.V. Ponomareva et al., 1991).
The obtained data on the simplification of the component composition of the SGP while enhancing brain acidification allow us to conclude that the development of neurodegeneration is accompanied by an increase in acidosis. A decrease in pH suppresses neuronal activity, and in the damaged brain this factor may be sufficient to disrupt the generation of late components of the VEP (U. Bonnet et al., 2000).
So, with BA, cerebral energy metabolism significantly changes: glucose consumption is reduced and its aerobic metabolism is disturbed. An important factor contributing to these disorders is a decrease in the activity of the enzymes of the mitochondrial respiratory chain, which causes the electrons to “slip away” from the respiratory chain and form highly active free oxygen radicals. Free-radical processes damage cellular structures and increase the formation of cross-links in beta-amyloid, which contribute to the accumulation of its insoluble deposits. Impaired aerobic oxidation of glucose leads to a relative predominance of anaerobic oxidation and the development of acidosis, which suppresses neuronal activity, and in addition, aggravates metabolic disorders, increasing mitochondrial dysfunction.
The increase in SCD observed in asthma clearly reflects a decrease in cerebral pH. Violations of SCP depend on the form and stage of the disease and are generally more pronounced in the presenile type of BA in the later stages of the disease. In asthma with a late onset, changes in SCP indicate less significant acidification of the brain than in asthma with an early onset. An increase in AMR in patients with asthma is one of the manifestations of stress- like metabolic changes and is accompanied by an increase in the level of the stress hormone cortisol. Cerebral acidosis intensifies free-radical processes that play a significant role in the pathogenesis of AD. Violations of information processes, according to the analysis of evoked potentials, are more significant with a more pronounced increase in SCP and, accordingly, a decrease in brain pH.