Bootstrapping the auditory space map via an innate circuit

The ability to accurately localize sound sources is crucial for human and other

animals. An important question is: how could the brain calibrate its space map

in response to changes to acoustic cues during a lifetime (e.g. in development,

aging, sensory loss)? Currently we still lack a comprehensive answer. Existing

models have focused on supervised learning, in which the auditory system is

calibrated by exactly matching feedback signals from the precise visual system.

But such cross-sensory calibration is not always feasible. It is unclear how to

calibrate the auditory map when sounds come from directions outside the visual

field, or how do congenitally blind people develop equivalent or in some cases

superior auditory localization skills. Therefore, the question to ask is: are there

alternative mechanisms beside supervised learning? More specifically, without

precise cross-sensory feedback, can the auditory system efficiently calibrate it-

self? To address these questions, we propose various self-calibration mechanisms

using only simple uni-sensory neural components, such as a circuit composed of

ipsilateral excitation and contralateral inhibition that can only distinguish left

from right(e.g. circuits for the lateral superior olive). At first glance, it seems

unlikely that such a simple circuit can be sufficient to calibrate a precise audi-

tory space map, since the simple circuit itself is noisy and much less precise than

the needed map. But surprisingly, numerical experiments show that a precise

map can actually be bootstrapped from a simple circuit alone, without exact

external feedback. This finding suggests an unexpected role of innate circuits

for self-calibration within the auditory system, prompting further investigation

via psychological and physiological experiments. It also reveals a broader di-

versity of potential learning mechanisms than previously assumed. Numerous

questions remain open for future research: When will a learning mechanism be

activated? Are different mechanisms competitive or complementary? Answers

to such questions may shed light on general learning mechanisms of sensory

systems and help with clinical practices for development and rehabilitation.