Signal Processing in the Brainstem Auditory Nuclei
Neurons in ascending auditory nuclei are specialized to extract and process the sound signals that are encoded as firing patterns of auditory nerve fibers (ANFs). Sound representing temporal or level features are extracted and transmitted in separate auditory pathways. The interaural difference signal of each sound feature, such as the interaural time difference (TD) or interaural level difference (ILD), is also processed and encoded as new signals in separate auditory nuclei in the brainstem. Accordingly, the temporal and the level signal of sounds are considered independent and to have different roles in the auditory system. However, they are interactive with each other, and enhance precision of the sound source localization cooperatively. The processing of temporal information ITD is affected by sound level signal through the inhibitory circuits, and the sound-phase signal affected the processing of ILD and direction sensitivity of the ILD-sensitive neurons. We investigated the auditory signal processing in the chicken brainstem nuclei. This selection of experimental animal was somewhat accidental as I have stated it already (in preface). However, the avian species was turned out to be one of the ideal species for auditory research because of the simplicity in structure of neural networks. Despite of the simplicity, the sound features are processed based on the same principle as that in the mammalian auditory system.
KeywordsCoincidence detection Feature extraction Binaural processing Interaural time difference Interaural level difference Inhibitory circuits
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