Prof. Bibikov Nikolay Grigorievitch
N.N.Andreyev Acoustics Institute, Russia
Temporal Analysis of The Sound in Auditory System of The Frog

It is now clear that the main role of the brain direct auditory pathway in is the detailed analysis of the current temporary signal in certain frequency channels. We have analyzed the mechanisms of temporal analysis of audio signals in the frog’s medulla (dorsal nucleus) and midbrain (semicircular torus)neurons. Tones, modulated in amplitude by repetitive noise segments in the frequency range 0-15 Hz were used as signals. Our objective was to identify the temporal features of the signal, which causes the cell response. Experimental evaluation of the correlation between sequences of the spikes induced by different repetitive portions of the envelope (shifted correlation) reveals the general characteristics of their output activity. The comparison of shifted correlation with the conventional autocorrelation function allowed us to assess the dynamics of the changes in the postspike excitability. The direct comparison of the response to some peculiarities of the envelope provided information about signal characteristics (f.e. rise or fall in amplitude) that evokes the spike reaction. Our results demonstrate that along the course of the auditory pathway the temporal characteristics of the single neuron’s signals become significantly more complex. The medullar neurons are usually characterized by half-wave envelope rectification. In auditory centers of the midbrain most cells react not to the signal amplitude but to its rate of change. Moreover, there is a strong dependence of the response on the presence of previous events. In many neurons previous events cause long postspike decrease of excitability. However, in a few cells the facilitation of the response in certain time interval after spike generation is apparent. Key words: amplitude modulation, shifted correlation, frog, envelope coging


I was born on February 13, 1940 in Moscow. After graduating from school with honors, in 1957, I became a student of the Physics Faculty of the Moscow State University named after M.V. Lomonosov. Just at this time in this Faculty some group of enthusiasts organized a new Department of Biophysics, and it is not surprising that this new direction for the faculty attracted my attention. Since then, my scientific interests were connected with the study of physical and physiological processes in living systems, especially in the auditory system. In 1963 I graduated from the Faculty of Physics at the Department of Biophysics and began working in the bioacoustics laboratory of the Acoustics Institute, headed by acad. N.N. Andreyev and later by prof. N.A. Dubrovsky. In the lab I went through all the stages of scientific career, from laboratory assistant to the head of the laboratory. The scientific interest area of my work is to study the mechanisms of acoustic signal processing in the auditory system of humans and animals. From the very beginning of the work some simple but effective methods were used for analyzing of auditory neurons characteristics in the frog’s brainstem. Using conditional probability methods I have shown that many of the reaction features of the peripheral neurons are determined by the existence of powerful noise component which is independent in different neural elements. This approach has allowed to develop original techniques for the assessment of synaptic intracellular potential, caused by the stimulus, without the traumatic intracellular recording. A similar approach allows to estimate the changes in the excitability of the cells of the auditory system after the generation of nerve impulses. The first application of correlation methods in the auditory system and, in particular, the method of the inverse trigger correlation allowed to identify characteristics of an audio signal that cause nerve cell response. We were the first to describe in frog’s auditory system the auditory neurons with high sensitivity to interaural delays, and other cells which are highly sensitive to differences in interaural intensity. Such neurons should be the basis of the ability of these animals to localize sounds. A modern research activity associated with stimulus-specific adaptation, partly began from my article: “Novelty neurons in the auditory system of the frog”; published in 1977. Of particular importance to my research is the study of dynamic characteristics of single neurons. We were the first to demonstrate a significant increase in the differential sensitivity of auditory units to changes in the amplitude during the process of adaptation. We have also shown that this process has at least two stages: a short-term, occupying less than 1s, and long-term, lasting more than 10 seconds. Also in the adapted state I have demonstrated a vivid manifestation of the stochastic resonance effect , when only the addition of a noise component in the baseband function allows units to reproduce very weak periodic modulation. Several important effects, first described in the frog’s auditory units were then demonstrated in mammals and even in psychophysical experiments on humans. A number of my papers on areas not directly related to the study of single neurons activity in the auditory system should also be mentioned. Among them the pioneering work of registering the activity of snapping shrimps of Far East coast of Russia, and biological sounds in the open ocean associated with daily migrations of fish and cephalopods. I was the first to register auditory brainstem responses by completely atraumatic method from the surface of the head in dolphins. My publication list includes more than 200 titles in various Russian and foreign scientific journals. I went on scientific trips to Germany, USA, Denmark. Special interest for me were my three scientific visits in China. I worked with colleagues from Institute of Biophysics (Beijing) and in Wuhan Normal University. I am interested in Russian wooden architecture and in some events of the Russian history, as reflected in several publications.

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