Zebra Finches Teach Us About Learning
By Christina Phillis
The zebra finch may be the epitome of the idiom: You can’t teach an old dog new tricks. Some zebra finches don’t retain the ability to learn new songs as they get older, but the reasons are not what you might expect.
Surprisingly, finches lose this ability only if they were tutored in their youth. Finches that weren’t taught specific songs are still able to learn. This peculiarity was the focus of a recent study, which discovered that experience can cause changes to the structure of genomic DNA that consequently affects the ability to learn.
What’s in a Song?
The zebra finch is commonly found in Australia, and only the males can learn and memorize songs. They learn a single song from an adult during the critical period of 30 to 65 days after hatching. That song forms the basis for a new, unique song that they create and use for the remainder of their lives. Once zebra finches pass that early critical period, tutored juvenile finches lose their ability to learn new songs and untutored finches, oddly, retain their learning abilities.
To test their hypothesis, a team led by Sarah London, an assistant professor in the Department of Psychology at the University of Chicago, isolated a set of male juvenile finches during their critical periods. A second set of birds received tutoring during the same period.
Researchers witnessed different epigenetic changes in the brains of tutored versus isolated finches, which resulted in modifications of the structural properties of their genomic DNA. This indicates a link between the epigenetic process that allows experience to trigger gene expression, and the gene expression that is required for tutored song memorization.
The results showed that regulatory factors known to have a role in learning and memory are overrepresented in the genes of the isolated birds.
Behind all of these complex processes is the confirmed presence of a specific neural signal in the brains of juvenile zebra finches: the mechanistic Target of Rapamycin or mTOR cascade. When the birds hear a song, the mTOR cascade is activated.
“We had evidence from other lab studies that mTOR inhibition disrupted learning events, and we had evidence that its activation did also, but not a good comparison. We wanted to directly test both activation and inhibition side by side in the same experiment,” London said.
The team analyzed the song patterns of adult tutors and their juvenile pupils using software designed for vocal comparison. When researchers enhanced or inhibited the mTOR activation, both actions caused a decrease in the bird’s ability to mimic the adult song. When mTOR activation was modified, juvenile birds retained the ability to learn songs but could not reproduce entire song structures.
The results from this study may help us to better understand early-life experiences and their effects on behavior and functions of the brain. mTOR regulates protein synthesis, an important factor in long-term memory formation, and mTOR-related disruptions are associated with autism and other memory-related conditions.
“In the last 5 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, where there’s a developmental event that requires social interactions, and a communication behavior that is hard to study in rodents who don’t typically learn vocalizations,” said London.
Another potential application is using learning inhibition to prevent patients from forming long-term memories of trauma. Researchers also hope that the capabilities of disadvantaged children could be boosted if we had a better understanding of how young children learn.
From advancing children’s abilities to demystifying complex neurological disorders, the results of this study open up a wide range of possibilities and once again prove that we never stop learning.