Posts tagged songbirds
Articles and news from the latest research reports.
Dying brain cells cue new brain cells to grow in songbird
Brain cells that multiply to help birds sing their best during breeding season are known to die back naturally later in the year. For the first time researchers have described the series of events that cues new neuron growth each spring, and it all appears to start with a signal from the expiring cells the previous fall that primes the brain to start producing stem cells.
If scientists can further tap into the process and understand how those signals work, it might lead to ways to exploit these signals and encourage replacement of cells in human brains that have lost neurons naturally because of aging, severe depression or Alzheimer’s disease, said Tracy Larson, a University of Washington doctoral student in biology. She’s lead author of a paper in the Sept. 23 Journal of Neuroscience on brain cell birth that follows natural brain cell death.
Neuroscientists have long known that new neurons are generated in the adult brains of many animals, but the birth of new neurons – or neurogenesis – appears to be limited in mammals and humans, especially where new neurons are generated after there’s been a blow to the head, stroke or some other physical loss of brain cells, Larson said. That process, referred to as “regenerative” neurogenesis, has been studied in mammals since the 1990s.
This is the first published study to examine the brain’s ability to replace cells that have been lost naturally, Larson said.
“Many neurodegenerative disorders are not injury-induced,” the co-authors write, “so it is critical to determine if and how reactive neurogenesis occurs under non-injury-induced neurodegenerative conditions.”
The researchers worked with Gambel’s white-crowned sparrows, a medium-sized species 7 inches (18 centimeters) long that breeds in Alaska, then winters in California and Mexico. Sometimes in flocks of more than 100 birds, they can be so plentiful in parts of California that they are considered pests. The ones in this work came from Eastern Washington.
Like most songbirds, Gambel’s white-crowned sparrows experience growth in the area of the brain that controls song output during the breeding season when a superior song helps them attract mates and define their territories. At the end of the season, probably because having extra cells exacts a toll in terms of energy and steroids they require, the cells begin dying naturally and the bird’s song degrades.
Gambel’s white-crowned sparrows are particularly good to work with because their breeding cycle is closely tied to the amount of sunlight they receive. Give them 20 hours of light in the lab, along with the right increase of steroids, and they are ready to breed. Cut the light to eight to 12 hours and taper the steroids, the breeding behavior ends.
“As the hormone levels decrease, the cells in the part of the brain controlling song no longer have the signal to ‘stay alive,’” Larson said. “Those cells undergo programmed cell death – or cell suicide as some call it. As those cells die it is likely they are releasing some kind of signal that somehow gets transmitted to the stem cells that reside in the brain. Whatever that signal is then triggers those cells to divide and replace the loss of the cell that sent the signal to begin with.”
The next spring, all that’s needed is for steroids to ramp up and new cells start to proliferate in the song center of the brain.
“This paper doesn’t describe the exact nature of the signals that stimulate proliferation,” Larson said. “We’re just describing the phenomenon that there is this connection between cells dying and this stem cell proliferation. Finding the signal is the next step.”
“Tracy really nailed this down by going in and blocking cell death at the end of the breeding season,” said Eliot Brenowitz, UW professor of psychology and of biology, and co-author on the paper. “There are chemicals you can use to turn off the cell suicide pathway. When this was done, far fewer stem cells divided. You don’t get that big uptick in new neurons being born. That’s important because it shows there’s something about the cells dying that turns on the replacement process.’
“There’s no reason to think what goes on in a bird brain doesn’t also go on in mammal brains, in human brains,” Brenowitz said. “As far as we know, the molecules are the same, the pathways are the same, the hormones are the same. That’s the ultimate purpose of all this, to identify these molecular mechanisms that will be of use in repairing human brains.”
In mammals, the area of the brain that controls the sense of smell and the one that is thought to have a role in memories can produce tiny numbers of new brain cells but it is not understood how or why. The numbers of new cells is so low that trying to identify and quantify whether dying cells are being replaced and if so, the steps that are involved, is much more difficult than when using a songbird like Gambel’s white-crowned sparrow, Larson and Brenowitz said.
What songbirds tell us about how we learn
When you throw a wild pitch or sing a flat note, it could be that your basal ganglia made you do it. This area in the middle of the brain is involved in motor control and learning. And one reason for that errant toss or off-key note may be that your brain prompted you to vary your behavior to help you learn, from trial-and-error, to perform better.
But how does the brain do this, how does it cause you to vary your behavior?
Along with researchers from the University of California, San Francisco, Indian Institute of Science Education and Research and Duke University, Professor Sarah Woolley, Department of Biology, investigated this question in songbirds, which learn their songs during development in a manner similar to how humans learn to speak. In particular, songbirds memorize the song of their father or tutor, then practice that song until they can produce a similar song.
“As adults, they continue to produce this learned song, but what’s interesting is that they keep it just a little bit variable” says Woolley. “The variability isn’t a default, it isn’t that they can’t produce a better version, they can — in particular when they sing to a female. So when they sing alone and their song is variable it’s because they are actively making it that way.”
The team used this change in the variability of the song to look at how the activity of single cells in different parts of the brain altered their activity depending on the social environment.
“We found that the social modulation of variability emerged within the basal ganglia, a brain area known to be important for learning and producing movements not only in birds but also in mammals, including humans” says Woolley. “This indicates that one way that the basal ganglia may be important in motor learning across species is through its involvement in generating variability.”
The researchers studied song birds because they have a cortical-basal ganglia circuit that is specific for singing. In contrast, for most behaviors in other species, the cortical-basal ganglia cells and circuits that are important for particular behaviors, like learning to walk, may be situated right next to, or even intermingled with cells and circuits important for other behaviors. “The evolution in songbirds of an identifiable circuit for a single complex behavior gives us a tremendous advantage as we try to parse out exactly what these parts of the brain do and how they do it,” says Woolley.
Useful for Parkinson’s disease
The basal ganglia is dramatically affected in illnesses such as Parkinson’s and Huntington disease. The team’s findings may eventually be relevant to understanding changes to learning and flexibility in movement that occur in those diseases.
“These are the kind of questions that we are now starting to pursue in the lab: how variability is affected when you radically manipulate the system akin to what happens during disease”, says Woolley.
(Source: mcgill.ca)
Genetic Defect Keeps Verbal Cues From Hitting the Mark
A genetic defect that profoundly affects speech in humans also disrupts the ability of songbirds to sing effective courtship tunes. This defect in a gene called FoxP2 renders the brain circuitry insensitive to feel-good chemicals that serve as a reward for speaking the correct syllable or hitting the right note, a recent study shows.
The research, which was conducted in adult zebrafinches, gives insight into how this genetic mutation impairs a network of nerve cells to cause the stuttering and stammering typical of people with FoxP2 mutations. It appears Nov. 21 in an early online edition of the journal Neuron.
"Our results integrate a lot of different observations that have accrued on the FoxP2 mutation and cast a different perspective on what this mutation is doing," said Richard Mooney, Ph.D., the George Barth Geller professor of neurobiology at Duke University School of Medicine and a member of the Duke Institute for Brain Sciences. "FoxP2 mutations do not simply result in a cognitive or learning deficit, but also produce an ongoing motor deficit. Individuals with these mutations can still learn and can still improve; it is just harder for them to reliably hit the right mark."
About 15 years ago, researchers discovered a British family with many members suffering from severe speech and language deficits. Geneticists eventually pinned down the culprit — a gene called forkhead box transcription factor or FoxP2 — that was mutated in all the affected individuals. The discovery led many to believe FoxP2 was a “language gene” that granted humans the ability to speak. But further studies showed that the gene wasn’t unique to humans, and in fact was conserved among all vertebrates, including songbirds.
Though the gene is present in every cell, it is “active,” or turned on, mostly in brain cells, particularly ones residing in a region deep within the brain known as the basal ganglia. This region is dysfunctional in Tourette syndrome, known for its vocal tics and outbursts, and is also shrunk in individuals with FoxP2 mutations.
To explore the complex circuitry involved in these deficits, Mooney and his former graduate student Malavika Murugan, Ph.D., decided to replicate the human mutation in this region of the brain in songbirds. Zebrafinches start learning how to sing 30 days after they hatch, listening to a male tutor and then practicing thousands of times a day until, 60 days later, they are able to make a very good copy of the tutor’s song. As good as that copy is at day 90, the male finch’s song gets even more precise when he “directs” it to a female as part of courtship.
To investigate the role of FoxP2 in the generation of this directed song, Murugan introduced specifically targeted sequences of RNA to suppress FoxP2 activity in the basal ganglia of male zebrafinches. The birds were placed in a glass cage that revealed a female sitting on the other side. Murugan then recorded sonograms of their song to capture the subtle vocal variations indistinguishable to the human ear when they produced directed songs at the female.
Murugan found that though the genetically manipulated males had already learned how to sing, their ability to hit the right note repeatedly in the presence of a female — a behavior critical to attracting a mate — was subpar. This indicates that in songbirds, FoxP2 has an ongoing role in vocal control separate from a role in learning, a distinction that has not been possible to make in humans with FOXP2 mutations.
Having deduced the behavior associated with this genetic mutation, the researchers then identified underlying neural deficits by recording brain activity in birds with normal and altered FoxP2 genes. In one set of experiments, Murugan sent an electrical signal into the input side of the basal ganglia pathway and then used an electrode on the output side to measure how quickly the signal traveled from one side to the other. Surprisingly, the signal moved more quickly through the basal ganglia of FoxP2 mutant songbirds than it did in songbirds with the functional gene.
Murugan also found that dopamine, an important brain chemical involved in brain signaling and the reinforcement of learned behaviors like singing or playing sports, could influence how fast basal ganglia signals propagated in birds with normal but not mutant forms of FoxP2.
"This switch between undirected and directed song is actually dependent on the influx of this neurotransmitter called dopamine," said Murugan, first author of the study. "So what we think is happening is knocking down FoxP2 makes the male incapable of reducing song variability in the presence of a female. An adult male sees the female, there is an influx of dopamine, but because the system is insensitive, the dopamine has no effect and the adult male continues to sing a variable tune." In juveniles, the inability to constrain variability and to respond to dopamine could also account for poor learning.
Though the researchers are cautious not to draw too many parallels between their findings in birds and the deficits in humans, they think their study does highlight the value of songbirds in studying human behaviors and disease.
"Birds are one of the few non-human animals that learn to vocalize," said Mooney. "They produce songs for courtship that they culturally transmit from one generation to the next. Their brains might be a thousandth the size of ours, but in this one dimension, vocal learning, they are our equal."
(Source: today.duke.edu)
Most songbirds learn their songs from an adult model, mostly from the father. However, there are relatively large differences in the accuracy how these songs are copied. Researchers from the Max Planck Institute for Ornithology in Seewiesen now found in juvenile zebra finches a possible mechanism that is responsible for the differences in the intensity of song learning. They provided the nerve growth factor “BDNF” to the song control system in the brain. With this treatment the learning ability in juvenile males could be enhanced in such a way that they were able to copy the songs of the father as good as it had been observed in the best learners in a zebra finch nest.
The improvement of cognitive abilities plays an important role in the therapy of neurological and psychiatric diseases. In this context research focusses more and more on the protein BDNF (Brain Derived Neurotrophic Factor). BDNF is mainly responsible for the preservation, growth and differentiation of nerve cells. Moreover, from experiments in mice it is known that BDNF enhances the ability to solve complex cognitive tasks.
In a learning experiment with zebra finches, researchers from the Max Planck Institute for Ornithology in Seewiesen in collaboration with scientists from the Free University of Amsterdam could now show for the first time in songbirds that BDNF acts as cognitive enhancer. They investigated zebra finch brother pairs that grew up with their genetic parents. In this setup juvenile birds will readily learn the songs from their fathers. However there are differences in the intensity of song learning among siblings of the same age. The worst learners have only a similarity of 20% with their fathers’ songs, whereas the best learners copy almost the entire songs of their fathers.
By now knowing the normal distribution of the learned songs within a zebra finch nest, as a next step the researchers were able to investigate the impact of BDNF on song learning. In one of the two brothers they enhanced the expression of BDNF in the song control system in the brain while the other brother did not get such a treatment. By analysing the songs the researchers found that those sons that received more BDNF had a higher similarity with the song of their fathers compared to normally reared juveniles. Remarkably, the learning efficiency in the BDNF-treated birds was as high as it has been previously observed in the best learners within the nest. This was due to an earlier onset of syllable copying in BDNF-treated birds and these birds also copied more and sang fewer improvised syllables. Therefore it is likely that the presence of BDNF in the song control system could correct possible inaccuracies in the song learning process, state the scientists around Manfred Gahr, who is the senior author of the study.
Discovery helps to unlock brain’s speech-learning mechanism
USC scientists have discovered a population of neurons in the brains of juvenile songbirds that are necessary for allowing the birds to recognize the vocal sounds they are learning to imitate.
These neurons encode a memory of learned vocal sounds and form a crucial (and hitherto only theorized) part of the neural system that allows songbirds to hear, imitate and learn its species’ songs — just as human infants acquire speech sounds.
The discovery will allow scientists to uncover the exact neural mechanisms that allow songbirds to hear their own self-produced songs, compare them to the memory of the song that they are trying to imitate and then adjust their vocalizations accordingly.
Because this brain-behavior system is thought to be a model for how human infants learn to speak, understanding it could prove crucial to future understanding and treatment of language disorders in children. In both songbirds and humans, feedback of self-produced vocalizations is compared to memorized vocal sounds and progressively refined to achieve a correct imitation.
“Every neurodevelopmental disorder you can think of — including Tourette syndrome, autism and Rett syndrome — entails in some way a breakdown in auditory processing and vocal communication,” said Sarah Bottjer, senior author of an article on the research that appears in the Journal of Neuroscience on Sept. 4. “Understanding mechanisms of vocal learning at a cellular level is a huge step toward being able to someday address the biological issues behind the behavioral issues.”
Bottjer professor of neurobiology at the USC Dornsife College of Letters, Arts and Sciences, collaborated with lead author Jennifer Achiro, a graduate student at USC, to examine the activity of neurons in songbirds’ brains using electrodes to record the activity of individual neurons.
In the basal ganglia — a complex system of neurons in the brain responsible for, among other things, procedural learning — Bottjer and Achiro were able to isolate two different types of neurons in young songbirds: ones that were activated only when the birds heard themselves singing and others that were activated only when the birds heard the songs of adult birds that they were trying to imitate.
The two sets of neurons allow the songbirds to recognize both their current behavior and a goal behavior that they would like to achieve.
“The process of learning speech requires the brain to compare feedback of current vocal behavior to a memory of target vocal sounds,” Achiro said. “The discovery of these two distinct populations of neurons means that this brain region contains separate neural representation of current and goal behaviors. Now, for the first time, we can test how these two neural representations are compared so that correct matches between the two are somehow rewarded.”
The next step for scientists will be to learn how the brain rewards correct matches between feedback of current vocal behavior and the goal memory that depicts memorized vocal sounds as songbirds make progress in bringing their current behavior closer to their goal behavior, Bottjer said.
(Source: news.usc.edu)
Songbirds’ brains coordinate singing with intricate timing
As a bird sings, some neurons in its brain prepare to make the next sounds while others are synchronized with the current notes—a coordination of physical actions and brain activity that is needed to produce complex movements, new research at the University of Chicago shows.
In an article in the current issue of Nature, neuroscientist Daniel Margoliash and colleagues show, for the first time, how the brain is organized to govern skilled performance—a finding that may lead to new ways of understanding human speech production.
The new study shows that birds’ physical movements actually are made up of a multitude of smaller actions. “It is amazing that such small units of movements are encoded, and so precisely, at the level of the forebrain,” said Margoliash, a professor of organismal biology and anatomy and psychology at UChicago.
“This work provides new insight into how the physics of controlling vocal signals are represented in the brain to control vocalizations,” said Howard Nusbaum, a professor of psychology at UChicago and an expert on speech.
By decoding the neural representation of communication, Nusbaum explained, the research may shed light on speech problems such as stuttering or aphasia (a disorder following a stroke). And it offers an unusual window into how the brain and body carry out other kinds of complex movement, from throwing a ball to doing a backflip.
“A big question in muscle control is how the motor system organizes the dynamics of movement,” said Margoliash. Movements like reaching or grasping are difficult to study because they entail many variables, such as the angles of the shoulder, elbow, wrist and fingers; the forces of many muscles; and how these change over time,” he said.
"With all this complexity, it has been difficult to determine which of the many variables that describe movements are represented in the brain, and which of those are used to control movements," he said.
"It’s difficult to find a natural framework with which to analyze the activity of single neurons. The bird study provided us a perfect opportunity,” Margoliash said. Margoliash is a pioneer in the study of brain function in birds, with studies that include how learning occurs when a bird sleeps and recalls singing a song.
Roots of language in human and bird biology
The genes activated for human speech are similar to the ones used by singing songbirds, new experiments suggest.
These results, which are not yet published, show that gene products produced for speech in the cortical and basal ganglia regions of the human brain correspond to similar molecules in the vocal communication areas of the brains of zebra finches and budgerigars. But these molecules aren’t found in the brains of doves and quails — vocal birds that do not learn their sounds.
"The results suggest that similar behavior and neural connectivity for a convergent complex trait like speech and song are associated with many similar genetic changes," said Duke neurobiologist Erich Jarvis, a Howard Hughes Medical Institute investigator.
Jarvis studies the molecular pathways that songbirds use while learning to sing. In past experiments, he and his collaborators found that songbirds have a connection between the front part of their brain and nerves in the brainstem that control movement in muscles that make songs in birds. They’ve seen this circuit in a more primitive form related to ultrasonic mating calls in mice. Humans also have this motor learning pathway for speech.
From this and other work, Jarvis developed the motor theory for the origin of vocal learning, which describes how ancient brain systems used to control movement and motor learning evolved into brain systems for learning and producing song and spoken language.
Gustavo Arriaga, Eric P. Zhou, Erich D. Jarvis. Of Mice, Birds, and Men: The Mouse Ultrasonic Song System Has Some Features Similar to Humans and Song-Learning Birds. PLoS ONE
Gustavo Arriaga, Erich D. Jarvis. Mouse vocal communication system: Are ultrasounds learned or innate? Brain and Language
(Image: iStock)
The question ‘How do songbirds sing?’ is addressed in a study published in BioMed Central’s open access journal BMC Biology. High-field magnetic resonance imaging and micro-computed tomography have been used to construct stunning high resolution, 3D, images, as well as a data set “morphome” of the zebra finch (Taeniopygia guttata) vocal organ, the syrinx.
Like humans, songbirds learn their vocalizations by imitation. Since their songs are used for finding a mate and retaining territories, birdsong is very important for reproductive success.
The syrinx, located at the point where the trachea splits in two to send air to the lungs, is unique to birds and performs the same function as vocal cords in humans. Birds can have such a complete control over the syrinx, with sub-millisecond precision, that in some cases they are even able to mimic human speech.
Despite great inroads in uncovering the neural control of birdsong, the anatomy of the complex physical structures that generate sound have been less well understood.
The multinational team has generated interactive 3D PDF models of the syringeal skeleton, soft tissues, cartilaginous pads, and muscles affecting sound production. These models show in detail the delicate balance between strength, and lightness of bones and cartilage required to support and alter the vibrating membranes of the syrinx at superfast speeds.
Dr Coen Elemans, from the University of Southern Denmark, who led this study, explained, “This study provides the basis to analyze the micromechanics, and exact neural and muscular control of the syrinx. For example, we describe a cartilaginous structure which may allow the zebra finch to precisely control its songs by uncoupling sound frequency and volume.” In addition, the researchers found a previously unrecognized Y-shaped structure on the sternum which corresponds to the shape of the syrinx and could help stabilize sound production.
Doing the math for how songbirds learn to sing
Scientists studying how songbirds stay on key have developed a statistical explanation for why some things are harder for the brain to learn than others.
“We’ve built the first mathematical model that uses a bird’s previous sensorimotor experience to predict its ability to learn,” says Emory biologist Samuel Sober. “We hope it will help us understand the math of learning in other species, including humans.”
Sober conducted the research with physiologist Michael Brainard of the University of California, San Francisco.
Their results, showing that adult birds correct small errors in their songs more rapidly and robustly than large errors, were published in the Proceedings of the National Academy of Sciences (PNAS).
Sober’s lab uses Bengalese finches as a model for researching the mechanisms of how the brain learns to correct vocal mistakes.
The researchers wanted to quantify the relationship between the size of a vocal error, and the probability of the brain making a sensorimotor correction. The experiments were conducted on adult Bengalese finches outfitted with light-weight, miniature headphones.
As a bird sang into a microphone, the researchers used sound-processing equipment to trick the bird into thinking it was making vocal mistakes, by changing the bird’s pitch and altering the way the bird heard itself, in real-time.
“When we made small pitch shifts, the birds learned really well and corrected their errors rapidly,” Sober says. “As we made the pitch shifts bigger, the birds learned less well, until at a certain pitch, they stopped learning.”
The researchers used the data to develop a statistical model for the size of a vocal error and whether a bird learns, including the cut-off point for learning from sensorimotor mistakes. They are now developing additional experiments to test and refine the model.
“We hope that our mathematical framework for how songbirds learn to sing could help in the development of human behavioral therapies for vocal rehabilitation, as well as increase our general understanding of how the brain learns,” Sober says.