Study Reveals How Birds Detect the Source of a Specific Sound

Scientists at Nagoya University have made significant progress in their understanding of the brain circuitry in birds, allowing them to determine the source of a particular sound.

(Photo : YURI KADOBNOV/AFP via Getty Images)

Interaural Time Difference Detection 

Scientists have made significant progress in their understanding of the brain circuitry in birds, allowing them to determine the source of a particular sound.

This study will help scientists gain more knowledge that involving the basics of how mammals' brains compute the time difference between one sound that each individual hears. 

Interaural time difference detection by animals is accurate for a wide range of frequencies, Rei Yamada, a graduate student at Nagoya University's Graduate School of Medicine and an expert in cell physiology, explains. 

Dendrites, the multiple branches extending from a single nerve cell, each receive a unique sound frequency from one or the other ear, making this process extremely specialized, according to Phys.org.

However, it's not yet clear how all of this comes together to enable the detection of an interaural time difference. 

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Laser Experiments Conducted on Chicken Brain Slices

In order to better understand this process, Yamada and Hiroshi Kuba teamed up. On chicken brain slices, they used lasers to stimulate excitatory receptors in a region of the brain involved in sound localisation. After that, they ran simulations to help them better understand their first findings. 

According to Science Daily, researchers found a concentration of synapses, or connections between nerve cells, near the ends of lengthy dendrites that were specifically designed to carry impulses from low-frequency sounds. Even though it may seem counterintuitive, this grouping actually shaved off a significant amount of strength in signal transmission from dendritic to nerve cell. 

In order to maintain its ability to process time difference and position information, the nerve cell had to be able to handle intensive inputs from dendrites dedicated to each ear.

Many animals and even humans use the difference in time between the sounds heard by each ear to help them locate their source, according to Yamada.

Researchers would like to see if the link they discovered between brain anatomy and function holds true across species. To grasp the core principles of interaural time difference detection that birds and animals share with humans, scientists need to expand their research to mammalian brains.

(Photo : JIM WATSON/AFP via Getty Images)

How Bird's Head Contribute to Directional Hearing

According to Dr Hans Schnyder of Technische Universität München (TUM) in Germany, a bird's directional hearing is influenced by its head shape. Sound waves can be absorbed, reflected, or diffracted depending on where they contact the skull.

According to the experts, a bird's head totally blocks sound from certain directions while other sound waves penetrate past the head and stimulate a response in the opposite ear. 

The varied sound levels in each ear help the avian brain understand if a sound is originating from above or below it. Schnyder claims that birds use this method to pinpoint the source of a lateral sound. 

Having eyes on the sides of their heads gives birds a nearly 360-degree range of view. Having developed the ability to process lateral sounds from different elevations, they can combine information from their senses of hearing and vision to evade predators. 

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