Contribution Of The Subcortical Auditory Pathway To The Perception And Processing Of Sounds PDF Download

"The auditory scene that we face during our day life is highly complex. The human auditory system is able to allow us to maintain a conversation with another person whilst ignoring the surrounding sounds but, at the same time, keeping track of what is happening to detect unexpected sounds that can be critical for survival. This suggests that whilst listening, there is an ongoing storage of information about the sounds we have already heard and how they relate to each other, thus allowing the auditory system to form expectations at different levels of complexity about what is going to come. Indeed, repetitive stimulation has been shown to reduce auditory neural activity in the human cerebral cortex and this neural activity that represents immediate or remembered features of a sensory stimulus can be used as evidence when making simple perceptual decisions. Yet, before reaching the auditory cortex, incoming auditory information is deeply processed by nuclei in the subcortical ascending auditory pathway. In a series of three studies carried out in the University of Barcelona and the University of Jyväskylä, we recorded the auditory frequency – following response (FFR) to study the contribution of the subcortical auditory pathway to sound encoding and processing. The FFR to periodic complex sounds provides a non-invasive measure of the neural transcription of sounds, as well as how auditory experiences transform these representations. Although it has been considered as a correlate of subcortical sound encoding, recent studies challenged this assumption, demonstrating that FFR receives major contribution from the auditory cortex. The objective of the present PhD thesis is to investigate how stimulus statistics and temporal predictability modulate regularity encoding in the subcortical auditory pathway and how the encoding strength of sounds in this pathway influences the latter making of simple auditory perceptual decisions. Additionally, we aimed to further characterize the FFR by means of electroencephalography and magnetoencephalography to understand the role of the frequency of the eliciting stimuli and disentangle the anatomical contribution of the FFRs elicited to sounds of different frequencies. Together our findings support the view that regularity encoding spans across the auditory hierarchy. Going a step further, temporal predictability and the frequency of the incoming stimulation also affect the subcortical sound encoding, which is reflected in the making of latter simple auditory perceptual decisions. Indeed, the frequency is a crucial parameter, as the cortical contribution to the FFR is not observable when the frequency of the sounds is around 300 Hz. Overall, we conclude that the subcortical auditory pathway has an active role in the perception and processing of the incoming sounds, consistent with the hypothesis of a distributed network for perceptual organization. Additionally, although the FFR has a multi-generator nature, it can still be used as a window into human subcortical sound encoding when using the appropriate stimulus parameters." -- TDX.