Auditory feedback amplification occurs at hair cells, not in the brain

Evidence

Process the data neurally and feedback in real time, not in the auditory cortex or deep in the brain, but right at the hair cells, setting up neural, not mechanical, amplification and frequency detection loops. Outer hair cells feed back by actively contracting, affecting membranes and ultimately the inner cells, which send the data through the spiral ganglia. That such feedback exists is now established, but exactly how it works is not. — Eric J. Heller, Why You Hear What You Hear- An…, 1927

Categorization

• QUESTION: How do outer hair cell contractions achieve amplification and frequency tuning? The mechanism remains unresolved.
• XREF: Active feedback loops connect to similar active amplification ideas in physics and engineering systems.
• DEEPTHINKING: The counterintuitive idea that signal processing happens locally at the transducer rather than centrally is a paradigm-level point about how sensory systems work.