The Corticofugal System for Hearing: Recent Progress

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 97; no. 22; pp. 11807 - 11814
• Main Authors: Suga, Nobuo, Gao, Enquan, Zhang, Yunfeng, Ma, Xiaofeng, Olsen, John F.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 24.10.2000; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Series: Colloquium Paper
• Subjects: Animals; Audio frequencies; Auditory Cortex - anatomy & histology; Auditory Cortex - physiology; Auditory signals; Auditory system; Bats; Behavioral neuroscience; Brain; Chiroptera - physiology; corticofugal system; Ears & hearing; Electric stimulation; Hair Cells, Auditory - physiology; Hearing - physiology; Modulated signal processing; Neurology; Neurons; Papers from the National Academy of Sciences Colloquium on Auditory Neuroscience: Development, Transduction, and Integration; Positive feedback
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.97.22.11807

Peripheral auditory neurons are tuned to single frequencies of sound. In the central auditory system, excitatory (or facilitatory) and inhibitory neural interactions take place at multiple levels and produce neurons with sharp level-tolerant frequency-tuning curves, neurons tuned to parameters other than frequency, cochleotopic (frequency) maps, which are different from the peripheral cochleotopic map, and computational maps. The mechanisms to create the response properties of these neurons have been considered to be solely caused by divergent and convergent projections of neurons in the ascending auditory system. The recent research on the corticofugal (descending) auditory system, however, indicates that the corticofugal system adjusts and improves auditory signal processing by modulating neural responses and maps. The corticofugal function consists of at least the following subfunctions. (i) Egocentric selection for short-term modulation of auditory signal processing according to auditory experience. Egocentric selection, based on focused positive feedback associated with widespread lateral inhibition, is mediated by the cortical neural net working together with the corticofugal system. (ii) Reorganization for long-term modulation of the processing of behaviorally relevant auditory signals. Reorganization is based on egocentric selection working together with nonauditory systems. (iii) Gain control based on overall excitatory, facilitatory, or inhibitory corticofugal modulation. Egocentric selection can be viewed as selective gain control. (iv) Shaping (or even creation) of response properties of neurons. Filter properties of neurons in the frequency, amplitude, time, and spatial domains can be sharpened by the corticofugal system. Sharpening of tuning is one of the functions of egocentric selection.