Features of evoked brain activity neurodynamics under conditions of differentiating visual stimuli in people with hearing deprivation
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Abstract
Introduction. There are no investigations of brain processes in adults with the lack of hearing using EP methods and in complex with neurodynamic study. We suppose that integrative neurophysiological and neurodynamic approach will help to deepen our understanding of activating and regulating systems of brain under the conditions of processing visual information in the investigated persons with hearing deprivation.
Purpose. In this regard, the goal of the research is to find out the features of the evoked activity of the brain and neurodynamics under the conditions of differentiating visual irritators in persons with hearing deprivation.
Methods. The evoked activity of the brain is investigated according to the indicators of long latent (cortical) visual evoked potentials (LVEP); and neurodynamic characteristics – under the conditions of differentiating visual information. 30 healthy individuals aged 21-25 (control group) without hearing problems and 30 individuals of the same age with hearing deprivation are investigated. The registration of LVEP is performed with the help of computer complex “Nerocom” ХАІ Medica, in the screened sound- and light-isolated chamber in a sitting position with photo-stimulation of the right and left eye with eyes closed. Non-artifact is analyzed. While analyzing the obtained LVEP curves, the latent periods of Р1, P2, Р3 wave peaks are considered. The investigation of neurodynamics properties are performed on computer system according to the developed method and program “Diagnost-1”. The statistical analysis of the obtained results was carried out by the methods of mathematical statistics using Excel software package.
Results. The number of processed irritators during the reaction of differentiation was reliably higher in the investigated individuals with normal hearing compared with the individuals with auditory deprivation function (p<0.05). The time of reaching minimum signal exposition and the minimum time of reaction was reliable longer in the investigated individuals with auditory deprivation (p<0.05-0.01); it indicated lower speed characteristics of neurodynamics. To understand the features of cortical activity during the differentiation of visual information, the results of the evoked activity of the deaf persons’ brain was compared to the data of the investigated individuals with normal hearing. It was found that the latency of early components of visual EP in the persons with auditory system deprivation was less than in the investigated individuals with normal hearing. The obtained data show quicker perception of a signal and higher reactivity of cortical cells in the deaf persons at the first stages of information processing that occurs via the rapid sensory fibers of lemniscus projection systems, thalamus-cortical structures and the acquired cross-modal reorganization of the cortex due to the compensatory response of the brain to cell destruction. Besides, the given results confirm the existence of powerful reorganizational compensatory changes of the occipital cortex area of the brain in the deaf persons of the investigated age. The correlation analysis shows the relationship between the indicators of the number of the processed irritators, the time of minimum signal exposition and the duration of the latent period of Р2 component of EP (р<0.05). Concerning the latent period of Р3 component, it was found that cortical activity in response to light flashes was reliably lower in the investigated persons with auditory deprivation (р<0.01).
Originality. According to EP, the weak part of the brain mechanisms of processing visual information in the deaf individuals is the information stage which the final formation of corresponding reaction depends on.
Conclusion.
The correlation has been found between the neurodynamic indicators of the processed stimuli number, the time of signal minimum exposition and the duration of Р2 latent component of EP.
The initial stages of the evoked brain activity are characterized with the high level of neocortex cell reactivity in the subjects with the deprivation of auditory function.
Significantly lower reactivity of the brain mechanisms, which provide the final response stage of differentiation, has been found in the deaf individuals compared to the persons with normal hearing.
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