Researchers at the University of Chicago (UChicago) have found for the first time that a key protein complex in the brain is linked to the ability of young animals to learn behavioral patterns from adults.
A specific neural signal, the mechanistic Target of Rapamycin (mTOR) cascade, regulates the ability of juvenile zebra finches to form accurate memories of songs taught to them by adult birds, the research finds.
This suggests mTOR's function in regulating protein synthesis may be involved, since protein synthesis is known to be a key feature of long-term memory formation.
The results have potentially provided new insight into children affect by neurodevelopmental disorders, as disruptions related to mTOR have been associated with autism spectrum disorders in humans.
"In the last five to 10 years, there seems to be a convergence on the mTOR cascade as a common disrupted process in autism spectrum disorders. We are not investigating autism per se, but what got our attention was that the zebra finches model a similar kind of situation," said Sarah London, assistant professor in the Department of Psychology of UChicago.
For the study, the researchers first confirmed the mTOR cascade was present in the brain of a juvenile zebra finch, and then established the cascade was activated in the auditory forebrain when a bird heard a song. They found that temporarily pharmacologically inhibiting or enhancing mTOR activation in the auditory forebrain directly diminished the ability of the bird to copy song from an adult tutor.
When molecular signaling in the auditory forebrain was disrupted during daily encounters with adult tutors, young zebra finches produced shorter and less complex songs that no longer reflected the tutor's song. Using software specifically designed for vocal comparison, the researchers analyzed the song patterns of the adults and the juvenile males with whom they interacted. The juvenile birds whose mTOR activation was modified by drug infusions retained the ability to sing and to mimic acoustic elements of the tutor's songs, but were unable to duplicate entire song structures.
"We had evidence from other lab studies that mTOR inhibition disrupted learning events, and we had evidence that its activation did also, " London said.
In addition to measuring the effects on song copying, the researchers also determined how mTOR activation influenced social engagement. During birds' song interaction with tutors, they recorded the position of the young birds in and out of a "hot zone" near the tutor's perch. Birds who had pharmacologically elevated levels of mTOR activation demonstrated less engagement with the adults. This is similar to what has been observed in children diagnosed with autism spectrum disorders, who often have mutations predicted to increase levels of mTOR signaling.
The finding presents a new opportunity to understand mechanisms by which social interactions enhance vocal learning ability of zebra finches and children, London believes.
The research finding by UChicago has been published in the Proceedings of the National Academy of Sciences on July 24.