Inside the brains of birds: Zebra Finches

Findings from multiple different studies into the neurobiology of zebra finches have been published by recently.
The first comes from University of Illinois. When a zebra finch hears a new song from a member of its own species, the experience changes gene expression in its brain in unexpected ways, these researchers report. The sequential switching on and off of thousands of genes after a bird hears a new tune offers a new picture of memory in the songbird brain. The finding, detailed this month in the Proceedings of the National Academy of Sciences, was a surprise, said principal investigator David Clayton, a professor of cell and developmental biology at the University of Illinois. He and his colleagues had not expected to see so many genes involved, and thought that any changes in gene activity after a bird heard a new song would quickly dissipate. The new experiments uncovered three distinct profiles of gene expression in the brain. One is typical of a bird sitting alone in silence. A second profile appears quickly just after a bird hears a recorded song – but only if the song is new to the bird. A third profile then emerges 24 hours later, after the song has become familiar. In the study, each bird was kept in quiet isolation overnight before it heard a recording of a new song. The recording was then repeated every 10 seconds for up to three hours.The new study took a broad snapshot of gene activity in the brain. Using DNA microarray analysis, the researchers measured changes in levels of messenger RNAs in the auditory forebrain of finches exposed to a new song. These mRNAs are templates that allow the cell to translate individual genes into the proteins that do the work of the cells. Any surge or drop in the number of mRNAs in brain cells after a stimulus offers clues to how the brain is responding. Twenty-four hours after the initial stimulus, the pattern of activated genes was entirely different from that of the initial response, regardless of whether the bird heard the song again on day two or not, Clayton said. Those genes that were originally upregulated or downregulated had returned to baseline, and a new network of genes was engaged. A major focus of this new network appears to be the regulation of energy metabolism. This suggests a lot is still going on in the brain, Clayton said.

The second study was from researchers at MIT. It is said that learning complex skills like playing an instrument requires a sequence of movements that can take years to master. Last year, MIT neuroscientists reported that by studying the chirps of these tiny songbirds, they were able to identify how two distinct brain circuits contribute to this type of trial-and-error learning in different stages of life. Now, the researchers have gained new insights into a specific mechanism behind this learning. In a paper being published in the Proceedings of the National Academy of Sciences during the week of July 6, the scientists report that as zebra finches fine-tune their songs, the brain initially stores improvements in one brain pathway before transferring this learned information to the motor pathway for long-term storage. To train the birds, researchers monitored their singing and delivered white noise whenever a bird sang a particular syllable at a lower pitch than usual. On a particular day, after four hours of training in which the birds learned to raise the pitch, the researchers temporarily inactivated the AFP with a short-acting drug (tetrodotoxin, a neurotoxin that comes from the puffer fish). The pitch immediately slipped back to where it had been at the start of that day’s training session — suggesting that the recently learned changes were stored within the AFP. But the researchers found that over the course of 24 hours, the brain had transferred the newly learned information from the AFP to the motor pathway. The motor pathway was storing all of the accumulated pitch changes from previous training sessions.

Before and after sound clips can be heard at the MIT website, here.

Posted by Dennis on 07/21 at 06:58 PM