Auditory frequency-following response: pilot evaluation of novel stimulation and signal processing strategies in the clinical diagnosis of developmental disorders and cognitive decline

The so-called Frequency Following Response (FFR) is an electrical response generated by the brainstem and evoked by complex sounds such as a syllable. The FFR reflects the synchronized sound-evoke neural activity and can be used to study the integrity of sound processing in the brain. Specifically, the FFR highlights and preserves the temporal and spectral characteristics of the stimulus evoking it. This makes the FFR a potentially interesting tool for studying how the generation of sound is tightly bounded to communication. The FFR can also reflect the principles of sound processing in the brain, its malleability, and its stability. In clinical settings, the FFR analysis could be used for a better understanding of communication disorders, learning disabilities, and cognitive decline. In this dissertation, an analysis of the FFR evoked from different types of stimulation has been performed, the aim being to assess the stimulus that would be the most useful in diagnosing developmental disorders and cognitive decline. Multiple signal processing analyses have been conducted, both in the time and frequency domain, to extract parameters that could be used in the clinical setting. The dataset consists of recordings collected in different hospitals around the Veneto and Piemonte regions in 54 normal-hearing adult individuals using the Socrates device and Helix software produced by Hedera Biomedics Srl. Data of three individuals who had already been clinically diagnosed with various types of disorders were also used for preliminary comparison. The methods chosen to analyze the FFRs were autocorrelation, stimulus-to-response cross-correlation and response-to-response cross-correlation, spectrograms, cross-phaseogram, pitch tracking coefficients, and inter-trial consistencies in time and phase. Overall, the analyses conducted demonstrate that the use of FFR is promising; implementation on data of subjects with disorders, albeit preliminary, gave very interesting insights into their conditions and possible rehabilitation solutions. In future research, a larger dataset comprising both healthy and pathological subjects could facilitate the application of FFR in diagnostic, rehabilitative, and preventive contexts.