Bird Brains Revealed

Tuesday, July 24th, 2007--

Hear what the finches heard and see their brain response for yourself.

Henning Voss, assistant professor of physics in radiology at Citigroup Biomedical Imaging Center of Weill Cornell Medical College, explains how the team prepared the birds and what the brain images show. [Photos courtesy of Methodist Neurological Institute, Houston, Texas.]

Scientists are looking in the brains of songbirds for clues to human speech impediments like stuttering. For the first time, they've managed to image the brain activity of zebra finches while the birds listen to different songs. Using functional magnetic resonance imaging (fMRI), researchers found that different sounds triggered different responses in the birds' brains, according to a study published in the Proceedings of the National Academy of Sciences.

"The very fact that we are able to do fMRI imaging in such a small animal is a new thing," said Santosh Helekar, associate professor of neuroscience at the Methodist Neurological Institute in Houston, Texas and the lead author of the paper. "It's an innovation in itself."

Helekar hopes that fMRI will help him better understand where stuttering comes from. Young zebra finches learn their songs the same way children learn to speak—they listen to their fathers or other "tutors" and try to emulate the sounds they hear. "We think that it's a good model of human speech, because [singing] is a learned behavior just as speech is a learned behavior," said Helekar.

A small percentage of songbirds, however, develop repeated utterances in their songs—what seems like a bird stutter to Helekar. Helekar eventually wants to look for neurological differences between stuttering and normal birds as they develop.

Since its development in the 1990s, neuroscientists have used fMRI to study human brain activity. In animals, the technique is usually limited to anesthetized rats and mice, because any head movement can ruin the results. "We needed to have a system whereby the bird is still awake and able to consciously perceive the sound," said Helekar.

Helekar and his team found that they could mildly sedate the birds and immobilize them by gently inserting them into a soft plastic tube. Once inside, the bird was fitted with a miniaturized head coil and packed into a soundproof box equipped with headphones. Researchers then slid the whole enclosure into a clinical MRI scanner as they would with a human subject.

Active areas of the brain require more oxygen than inactive areas, and oxygenated blood has different magnetic properties than non-oxygenated blood. For fMRIs, the MRI machine creates a large magnetic field, and a head coil monitors the activation changes over time.

Zebra finch brains are only ten millimeters in diameter, so Helekar's team had to figure out how to create a miniature head coil with higher resolution than human scanners. "The challenge was to get as close to the head of the bird as possible, and to immobilize the head," said Henning Voss, first author on the paper and an assistant professor at Weill Cornell Medical College in New York, who helped develop the device.

Once the bird was inside the machine, it repeatedly heard two-second sound recordings followed by two seconds of silence. The researchers used recordings of the bird's own song, the song it learned from (its tutor's song), and the song of another bird it had never met, in addition to a simple tone.

"We are able to see subtle differences in the amount of activation and area of activation in response to different stimuli," said Helekar. The greatest activation came from the bird's own song, while the recording of the bird's tutor activated a larger area of the brain. They found that the birds had greater activation in the right hemisphere of the brain, consistent with similar fMRI studies of human language processing.

Voss and Helekar now plan to use their fMRI technique to study development—watching how brain activation changes as young birds learn their songs. "The next step is definitely to do developmental studies where we follow up the development of birds over time. We want to understand how the birds learn their song," said Voss.

-Joshua J Romero

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--Joshua Romero