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February 16, 2005

CCNY BIOLOGISTS LINK SLEEP, DEVELOPMENTAL LEA

Study of Bird Song Suggests Sleep Provides Base for New Learning

NEW YORK, February 16, 2005 – In a study that offers insight into developmental learning, biologists at The City College of New York and Cold Spring Harbor Laboratories have demonstrated that sleep strengthens the ability to learn and remember motor skills over the course of development.  Developmental learning (e.g. speech acquisition) takes place during early life and has effect that last an entire lifetime. 

The study was the first examination of the role of sleep in developmental learning and the first direct evidence that sleep affects learning in the juvenile, with consequences in adult life.  The findings, which were published in a cover story in Nature, February 17, were based on an examination of how sleep affects song learning in a juvenile bird.

Led by Dr. Sebastien Deregnaucourt, a CCNY postdoctoral student, and Dr. Ofer Tchernichovski, Associate Professor of Biology, researchers were able to show how night sleep affects song development in the song bird by recording and analyzing the birds’ entire song development (about one million syllables per bird).  “Birds are a good model for what occurs in humans because a bird learns his song similar to how humans learn to speak,” Dr. Tchernichovski said. 

Using sound analysis software developed at CCNY, the team summarized the structure of each song syllable produced by an array of acoustic features.  They then assessed song development by examining changes in feature values and by measuring how similarity emerges between the bird’s song and a “song model” played to the bird. 

They found that some vocal changes occur during the day, when the bird sings, but even stronger vocal changes occur at night, when the bird is asleep.  That is, when the bird wakes up in the morning, his song has changed from the previous day.

Changes in song structure that take place during sleep are qualitatively different from those that occur online, during singing.  In previous studies in adults, an immediate improvement in learned motor skills was observed after sleep.  However, in the juvenile bird, the team observed an opposite effect: a marked deterioration in the quality of the song structure immediately after night sleep.

Within three hours of intense morning singing, however, the birds recovered the structure of their song and were able to attain a new record in performance level.  Interestingly, while little additional improvement occurred before the next sleep episode, birds that showed stronger ‘deterioration’ after sleep achieved better learning as adults.

“Sleep turns a song plastic but enables it to improve over the day,” Dr. Tchernichovski said. “Good sleep doesn’t improve performance immediately, but it gives the bird an opportunity for new learning.”  The same pattern occurred whether the bird went to sleep naturally or when sleep was induced during the day using the hormone melatonin. 

The cover story on bird sleep is the second article by CCNY faculty to appear in Nature over the last four weeks.  In “Self Similarity of Complex Networks,” a “Letter to Nature” article published January 27, Dr. Hernan Makse, Assistant Professor of Physics, and co-workers show that complex networks, whether they occur in nature, society or technology, are self-similar.  This means a subsection of a network looks much the same as the entire thing, just as a branch on a tree resembles the whole tree.  The property of self similarity could explain how complex networks grow and self organize into their scale-free structure.

The study was the first examination of the role of sleep in developmental learning and the first direct evidence that sleep affects learning in the juvenile, with consequences in adult life.  The findings, which were published in a cover story in Nature, February 17, were based on an examination of how sleep affects song learning in a juvenile bird.

Led by Dr. Sebastien Deregnaucourt, a CCNY postdoctoral student, and Dr. Ofer Tchernichovski, Associate Professor of Biology, researchers were able to show how night sleep affects song development in the song bird by recording and analyzing the birds’ entire song development (about one million syllables per bird).  “Birds are a good model for what occurs in humans because a bird learns his song similar to how humans learn to speak,” Dr. Tchernichovski said. 

Using sound analysis software developed at CCNY, the team summarized the structure of each song syllable produced by an array of acoustic features.  They then assessed song development by examining changes in feature values and by measuring how similarity emerges between the bird’s song and a “song model” played to the bird. 

They found that some vocal changes occur during the day, when the bird sings, but even stronger vocal changes occur at night, when the bird is asleep.  That is, when the bird wakes up in the morning, his song has changed from the previous day.

Changes in song structure that take place during sleep are qualitatively different from those that occur online, during singing.  In previous studies in adults, an immediate improvement in learned motor skills was observed after sleep.  However, in the juvenile bird, the team observed an opposite effect: a marked deterioration in the quality of the song structure immediately after night sleep.

Within three hours of intense morning singing, however, the birds recovered the structure of their song and were able to attain a new record in performance level.  Interestingly, while little additional improvement occurred before the next sleep episode, birds that showed stronger ‘deterioration’ after sleep achieved better learning as adults.

“Sleep turns a song plastic but enables it to improve over the day,” Dr. Tchernichovski said. “Good sleep doesn’t improve performance immediately, but it gives the bird an opportunity for new learning.”  The same pattern occurred whether the bird went to sleep naturally or when sleep was induced during the day using the hormone melatonin. 

The cover story on bird sleep is the second article by CCNY faculty to appear in Nature over the last four weeks.  In “Self Similarity of Complex Networks,” a “Letter to Nature” article published January 27, Dr. Hernan Makse, Assistant Professor of Physics, and co-workers show that complex networks, whether they occur in nature, society or technology, are self-similar.  This means a subsection of a network looks much the same as the entire thing, just as a branch on a tree resembles the whole tree.  The property of self similarity could explain how complex networks grow and self organize into their scale-free structure.

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