The changes in the electrical activity of the brain of boys with different tempo-rhythmic characteristics of speech during functional stress have been studied, namely, a series of flashes of light of a certain frequency – rhythmic photostimulation have been used. The bioelectrical activity of the brain has been studied using a computer electroencephalography system. Also, according to the methodology of zonal distribution of normalized spectral power (SP) of the rhythm of the main frequency of the EEGranges, the particles (in percent) of the normalized SP of electrogenesis in each of the four main ranges (δ, θ, α, β) have been determined. As a result of comparison of the light flashing frequency assimilation among boys in the studied groups, it has been found, that in the group of children with logoneurosis slow rhythms (5 Hz,) lying within the theta-range of the EEG, were better assimilated. The rhythm is assimilated in the low frequency range among the children with logoneurosis. The relative spectral power of theta-rhythm significantly decreased on the EEG of children with tempo and rhythm speech disorder at low-frequency photostimulation in comparison with the corresponding indicators of the background electroencephalogram; the corresponding indicators in the beta-range, anterior and posterior leads in the alpha-rangeincreased. Based on the obtained data, it has been found, that children with logoneurosis have insufficient response to photostimulation. Such data are associated with insufficient inhibitory effect of the cortex on the subcortical structures. The reduced reactivity and functional insufficiency of the activating system of the brain stem have been noted. Neurophysiological mechanisms of logoneurosis are due to the state of insufficient formation of brain structures, which is confirmed by the results of electroencephalography during rhythmic photostimulation. Changes in the tempo and rhythm of speech during logoneurosis of preschool children provoke stress of the brain mechanisms of regulation, which become apparent by special characteristics of the electrical activity of the brain, both at rest and during load.