AsianScientist (Dec. 22, 2016) – In a collaborative study, neuroscientists and a physicist at the Okinawa Institute of Science and Technology Graduate University (OIST) have discovered that the silent gaps between birdsong syllables can be used to differentiate bird species. Their findings have been published in Science.
Baby birds preferentially learn the song of their own species, even in noisy environments with a variety of different birdsongs. But how they can recognize their own species’ song has, until now, remained a mystery.
The researchers performed a cross-fostering experiment in which juvenile zebra finches were raised by Bengalese finch foster parents to examine how their birdsong develops under the tutoring of a different species.
“The fostered zebra finches sang the Bengalese finch song with a zebra finch accent,” said study co-author Professor Yoko Yazaki-Sugiyama.
Birdsong is comprised of stereotypical repeats of a few syllables, called ‘song motifs,’ in which syllables are separated by silent gaps. To determine the neural basis of this innate species detection mechanism, the researchers recorded the activity of neurons in the auditory cortex of adult zebra finch brains during exposure to birdsong. They discovered a first set of neurons which registered temporal gaps of zebra finch songs, as well as a separate second set of neurons that are responsive to syllable morphology.
Using trains of song syllables or white noise separated by silent intervals of varying lengths, they discovered that the first set of neurons are most sensitive to silent gaps with the same duration as the silent gaps found in natural zebra finch song. The neurons did not respond to syllable trains if the duration between syllables was too short or too long. This phenomenon persisted in juvenile zebra finches raised in isolation or cross-fostered by Bengalese finch parents.
This first set of neurons responded strongly to natural zebra finch song. They neither responded to artificial zebra finch song in which the duration of the silent gaps between syllables had been increased, nor to the songs of other species. Together these findings support the existence of neuronal mechanisms that use silent gaps between syllables of birdsong to detect songs of the same species during learning.
“This first set of neurons operate as a kind of neural barcode reader,” Yazaki-Sugiyama explained.
Each male zebra finch has to develop a unique song that is different from other zebra finches, while maintaining species specific identity. Parallel processing of syllable morphology and temporal silent gaps between syllables discovered by OIST researchers could help explain how these two competing criteria are satisfied.
Decades ago, researchers at Bell Laboratories seeking to boost telecommunication channel capacity developed tools in voice activity detection as well as information theory. This interdisciplinary study used information theoretic tools and discovered similar strategies are hardwired in bird brains to recognize and learn songs of their own species, showing us that there is information in silence.
The article can be found at: Araki et al. (2016) Mind the Gap: Neural Coding of Species Identity in Birdsong Prosody.
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Source: Okinawa Institute of Science and Technology Graduate University.
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