Frequency following response (FFR): examining variability of this complex response

Abstract

One aspect of the frequency-following response (FFR) which reflects neural representation of pitch at the level of the brainstem that has proven difficult to explain is the significant amount of variability seen in the response, even within a group of normal hearing listeners (Ruggles, Bharadwaj, & Shinn-Cunningham, 2011). Such response variability has been attributed to a number of factors including but not limited to experience or training induced plasticity, gender and age of the subject, “hidden hearing loss”, stimulus parameters, analysis parameters, etc. The specific aims of this study were twofold: 1) to examine the effect of stimulus frequency on the FFR to low frequency pure tone stimuli (250, 500 and 1000 Hz) in a group of normal-hearing individuals, and 2) to examine subject-related variability in the brainstem neural encoding strength, specifically, if and how gender and varying degrees of musical experience are reflected in the neural encoding of a 500 Hz pure tone stimuli. The FFR was recorded to 250, 500, and 1000 Hz pure tone stimuli, in 30 normal hearing 19 29 year-old young adults (males = 12). A total of 4000 sweeps were collected at each frequency per participant, and data were analyzed by gender, and self-reported number of years of formal musical training. Results revealed a significant effect of stimulus frequency on FFR spectral amplitude. Additionally, there was a significant effect of gender, with females displaying greater spectral amplitudes than males at 500 Hz. The relationship between years of musical training and FFR amplitude was non-significant. These findings suggest that neural representation of pitch is greater for low frequency pure tone stimuli, when compared to frequencies, such as 1000 Hz, that are closer to the upper limits of phase locking in the human auditory brainstem. Additionally, the differences between males and females observed in the FFR amplitudes at 500 Hz, suggest that gender differences may be present in sub-cortical neural representations of simple auditory stimuli.