Researchers at the University of Chicago have identified key differences in epigenetic landscapes among zebra finch songbirds who differ in their ability to learn, which could influence how we can help trauma patients and young learners.
Sarah London, Assistant Professor in the Department of Psychology at the University of Chicago, has long appreciated zebra finches for their unique learning characteristics. Only male zebra finches learn to sing, and they learn through social interactions another male tutor. Tutor song learning occurs during development and is high-stakes; each male sings one song their entire adult lives, based on their tutor experience. Intriguingly, the ability to memorize tutor song is restricted to a “Critical Period” (CP), thus learning itself is the process that prevents the juvenile from continuing to learn new songs later. This learning property offers a unique opportunity to study how the brain learns, and how brain processes affect whether or not a mentor’s song is learned, London says.
The tiny song birds have proven invaluable to her research into how animals learn. “Developmental song learning in zebra finches is one of the most striking examples of a CP for complex learned behavior,” she says. “The learning experience has a profound and long-lasting effect on their neurological cognitive processes.”
London’s team recently completed a study demonstrating measurable and repeatable differences between epigenetic profiles of zebra finches who receive tutoring, and those that do not. These differences directly relate to levels and patterns of gene expression in the brains of finches that can still learn from a tutor compared to those that can no longer learn song. London co-authored a paper on this research entitled, Epigenetic regulation of transcriptional plasticity associated with developmental song learning, with Somayeh Ahmadiantehrani, a postdoctoral fellow at UChicago, which was published Wednesday, May 4 by the Proceedings of the Royal Society B.
Never too old to learn
The primary goal of London’s lab is to identify the neural properties that promote and limit the ability to learn, and she emphasizes research on zebra finch neural development and learning behaviors to identify these traits. In the current study, the team took advantage of the natural CP for mentored song learning to test the hypothesis that tutor experience within the CP alters mechanisms in the brain that control genome function. They hypothesized that this would explain how the tutor experience ends the CP for learning, while isolation from song during the CP extends the age at which juveniles can memorize tutor song.
In the study, coauthored with Theresa K. Kelly and Adam Blattler from Active Motif, she and her team isolated one set of male juvenile finches from male tutors during the CP of song learning, which occurs between 30 and 65 days post-hatch. A second group of juveniles did experience a tutor during the CP. “After day 65, whether or not a juvenile male can memorize a tutor’s song depends on his experiences in the month prior,” London explains. “If he experienced a tutor, he can no longer learn, but if he has been isolated from hearing a tutor he is still able to learn a song, suggesting a change in brain chemistry as a result of learning.”
After day 65, London’s team assayed the brains of both groups of finches to compare epigenetic landscapes, patterns of gene expression and cellular properties of the brain between males who experienced a tutor and those who had not. The results show that learning a tutor song induces specific epigenetic changes that do not occur in the brains of the isolated males, and vice versa. Among the findings was the fact that transcriptional regulatory factors well-studied for their role in learning and memory in juvenile zebra finches and other animals, such as the extracellular-signal-regulated kinase (ERK) pathway, are overrepresented in the set of genes predicted to be more highly expressed in the isolated birds. Because gene expression triggered by experience is necessary for learning and memory, these findings raise the possibility that the gene expression required for tutor song memorization is mechanistically linked to epigenetic processes that control the ability for subsequent tutor experience to trigger gene expression, thus preventing future tutor song memorization after day 65.
Lessons for trauma patients
London believes the results of this study could have future implications for helping trauma patients to prevent encoding those events into their long term memory; as well as advancing our understanding of how young children learn, and what can be done to enhance learning capabilities among disadvantaged youth in order to level the playing field of learning among children entering school. “These results help us understand complex genomes in the context of the everyday learning experience,” London says. “It decouples the actual experience from the genomic process happening in the brain, and this knowledge could be a guide to therapeutics.”
Going forward she plans to conduct future experiments testing causal relationships between epigenetic processes, learning and memory, and the extended ability to learn, with the continued goal to advance understanding of how learning is regulated in developing and mature animals.