# 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 $E\phantom{\rule{0}{0ex}}I$ 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 $10,000$ $E\phantom{\rule{0}{0ex}}I$ 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

More Features »

### Announcements

More Announcements »

## Previous Synopsis

Interdisciplinary Physics

Nanophysics

## Related Articles

Biological Physics

### Focus: How 1000 Bacterial Species Can Coexist

The surprising stability of large and diverse bacterial communities can be explained by a model that emphasizes the microbes’ food requirements. Read More »

Biological Physics

### Synopsis: Connecting Noisy Single-Cell Dynamics to Smooth Population Growth

A new theoretical framework connects the exponential growth of a cell population to the stochastic replication of individual cells within the population. Read More »

Nonlinear Dynamics

### Viewpoint: Brain Motion Under Impact

A numerical study suggests that head impacts primarily induce a few low-frequency, damped modes of vibration in brain tissue, a finding that could inform the design of sports helmets. Read More »