Peculiarities of Frequency-Following Response in Healthy Individuals when Listening to Complex Sounds

INTRODUCTION: Studies of recent years showed that functional disorders in the brainstem may be one of factors causing inability to perceive speech by normal-hearing individuals. Frequency-following response (FFR) is an auditory evoked potential emerging in different regions of the brain in response to a sound or a change in the sound frequency. The initiation of this potential is associated with the correct processing of auditory information in the subcortical structures of the brain. However, until the moment, there is no regulatory framework that could permit use of this potential in routine examinations. AIM: To identify and analyze the peculiarities of FFR in healthy adult individuals when listening to a complex sound. MATERIALS AND METHODS: The study included 29 healthy subjects aged from 18 to 48 years (mean age 28 ± 10 years). Electrical activity of the brain was recorded from 32 electrodes. Sampling frequency 2000 Hz, transmission frequency 0.1 Hz–500 Hz. The stimulus was a 30-s sound that included simple sounds of five different frequencies (600 Hz, 800 Hz, 1000 Hz, 2000 Hz, 4000 Hz) changing in a random order every 100 ms. FFR was isolated in each frequency change in the complex sound. The resulting FFR included two peaks, for each amplitude, latency, and dipole sources were calculated. RESULTS: FFR was obtained in all the subjects and included two peaks. In some subjects, FFR peaks had a statistically higher amplitude and lower latency. In subjects with a higher amplitude FFR peaks, three dipoles were identified for the first peak: in the brainstem and in the cortex of the right hemisphere (Brodmann areas 6 and 39). For the second peak, one dipole was identified in the cortex (Brodmann area 19). In subjects with low amplitude FFR peaks, for the first peak one source in the brainstem was identified. For the second peak, two dipoles were identified: in the posterior cingulate cortex (Brodmann area 23) and in the medial thalamus. CONCLUSION: The data obtained suggest that the method of recording and analyzing FFR can be used to assess the functional integrity and correct participation of the midbrain in the perception of auditory stimuli. The peculiarities of amplitude-time parameters of its peaks probably reflect the individual ability to finely differentiate stimuli.