Synopsis: Telling Left From Right

Large numbers of neurons can, according to a computational model, distinguish the timing of aural cues more finely than individual cells.

One way that animals, including humans, locate a sound source is by detecting slight differences in the arrival times of sound waves to the left and right ears. Animal auditory systems are capable of detecting interaural time differences of less than 100 microseconds, even though individual neurons respond on the relatively sluggish time scale of milliseconds.

Neurons are often modeled as electrical circuits, so understanding the timing sensitivity of the auditory system is analogous to designing a detector that operates faster than any of its components. Now, writing in Physical Review Letters, Viacheslav Vasilkov at Southern Federal University in Russia and Ruben Tikidji-Hamburyan at Louisiana State University, New Orleans, present a computational model to test the hypothesis that interaural sensitivity could be related to so-called EI neurons, found in the mid-brain section of the auditory system.

A long-standing model for interaural detection assumes neurons act as coincidence detectors, responding most strongly when signals from both ears arrive at the same time. In this picture, nerve fibers act as delay lines for certain cells, meaning these cells will respond only when a signal from one ear is sent earlier than the other.

Vasilkov and Tikidji-Hamburyan instead model the interaural detection system as a population of more than 10,000 EI cells, each of which receives excitation signals from one ear and inhibition signals from the other. In the authors’ model, the maximum membrane potential of any one cell depends on the time difference between the excitation and inhibition signal;
 thus different neurons reach threshold and start firing for different stimuli.
 A heterogeneous mixture of these cells, which combines the thousands of thresholds of individual cells, can, according to the authors, detect interaural timing differences with microsecond accuracy. – Jessica Thomas


Features

More Features »

Subject Areas

Nonlinear DynamicsBiological Physics

Previous Synopsis

Interdisciplinary Physics

The Unbearable Hardness of Physics

Read More »

Next Synopsis

Nanophysics

Half In, Half Out

Read More »

Related Articles

Synopsis: Jiggles that Help Bat Biosonar
Biological Physics

Synopsis: Jiggles that Help Bat Biosonar

The directional sensitivity of bat biosonar is improved by the wiggling of structures on the bat’s nose and ears. Read More »

Viewpoint: Searching for Order in Turbulent Flow
Fluid Dynamics

Viewpoint: Searching for Order in Turbulent Flow

The observation of ordered flow patterns in a weakly turbulent liquid may lead to new ways of predicting the evolution of turbulent flow. Read More »

Synopsis: Racing Bacteria
Biological Physics

Synopsis: Racing Bacteria

Bacteria track fast-moving chemical signals by hopping from one chemically favorable region to another. Read More »

More Articles