Benichov JI, Vallentin D. (2020). Inhibition within a premotor circuit controls the timing of vocal turn-taking in zebra finches. Nat Commun. 11(1):221.
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Zebra finches can take turns when exchanging short calls with one another, much like humans do during conversations. Researchers from the Max Planck Institute for Ornithology have now shed light on the underlying neural dynamics in a songbird brain area called HVC, or the so called “song control centre”. The researchers identified neurons involved in initiating a call as well as another class of neurons that inhibits neighboring cells shortly before a bird calls. The importance of these cells for vocal turn-taking was further supported by the observation that specific disruptions to the signaling of either type of neuron resulted in distinct changes in call timing.

Imagine if every time you started a conversation, the other person would speak as soon as you began talking. Not only would this be considered rude, it would be difficult to hear each other and the interaction would not get very far. In our everyday conversations we rely on our ability to take turns and to avoid speaking at the same time. We do this so effortlessly that we often take it for granted. This feat involves withholding or delaying our responses when we hear another person speaking and initiating our speech once they’ve stopped. In other words, what you hear does not only influence what you say but also when you say it.

Other animals perform similar back-and-forth vocal exchanges. However, the underlying neural mechanisms of this vocal turn taking were so far unknown. Therefore, Jonathan Benichov and Daniela Vallentin from the Max Planck Institute for Ornithology started a study with zebra finches, small Australian songbirds, to find out how they coordinate their simple short calls during interactions. It has been shown that a forebrain cortical region called HVC is centrally important for song learning and production. “We thought that this specialized area in the zebra finch brain is a good place to look for an explanation of how vocal turn-taking is achieved”, says Jonathan Benichov, first author of the study. This area is known to act like a metronome to control the tempo of the elaborate courtship song that males learn from a tutor as they grow up. Benichov and Vallentin found that neurons in this area are also important for controlling the timing of the simpler short calls used in ordinary social interactions. In this case the area can act like a traffic light that determines when to call and when to wait.

The researchers recorded from individual nerve cells in this brain area using electrodes that are 1/50th the width of a human hair. This is done with a lightweight electronic device that the bird can wear on its head while it moves around, sings, and interacts with another bird or with recordings of another bird’s calls. With this, they found that some brain cells in HVC were active a few milliseconds before a bird actually calls, hinting that these neurons are involved in initiating a call. They also found similar cells that had their activity turned down right before a bird’s call. “This led us to look at another type of cell that is known to quiet down neighboring cells”, explains Daniela Vallentin, head of the research group Neural circuits for vocal communication. These activity-suppressing cells turned out to be active before the cells that cause the bird to call, suggesting that they control when this call initiating signal occurs.

To test this directly, the researchers chemically blocked the action of these inhibitory cells and found that the call-initiating cells produced stronger and earlier signals. Moreover, the birds responded much faster to a partner and were more likely to interrupt the calls they heard.

Both humans and songbirds have specialized neural pathways which link hearing areas to vocal areas. Perhaps there are also parallels across species with respect to how we avoid interrupting each other.

(Sabine Spehn)

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 Benichov JI, Vallentin D. (2020) Inhibition within a premotor circuit controls the timing of vocal turn-taking in zebra finches. Nat Commun. 11(1):221.
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The post How a Bird Brain Times Tweets first appeared on Max Planck Neuroscience.

When a male or female white-browed sparrow-weaver begins its song, its partner joins in at a certain time. They duet with each other by singing in turn and precisely in tune. A team led by researchers from the Max Planck Institute for Ornithology in Seewiesen used mobile transmitters to simultaneously record neural and acoustic signals from pairs of birds singing duets in their natural habitat. They found that the nerve cell activity in the brain of the singing bird changes and synchronizes with its partner when the partner begins to sing. The brains of both animals then essentially function as one, which leads to the perfect duet.

White-browed sparrow-weavers (Plocepasser mahali) live together in small groups in trees in southern and eastern Africa. Each bird has a roosting nest with an entrance and an exit. The dominant pair will have a breeding nest which is easily recognisable by the fact that one passage is closed to prevent eggs from falling out. In addition to the dominant pair, there are up to eight other birds in the group that help build nests and raise the young. All group members defend their territory against rival groups through duets of the dominant pair and choruses together with the helpers.

White-browed sparrow-weavers are one of the few bird species that sing in duet. It was assumed that some cognitive coordination between individuals was required to synchronise the syllables in the duet, however the underlying neuronal mechanisms of such coordination were unknown.

Miniature transmitters enable recording under natural conditions
“White-browed sparrow-weavers cannot develop their complex social structure in the laboratory. We were therefore only able to investigate the mechanisms of the duet singing in the natural habitat of the birds”, says Cornelia Voigt, one of the three lead authors of the study. Because of this, researchers and technicians at the Max Planck Institute for Ornithology in Seewiesen developed mobile microphone transmitters to record the singing in the wild. These weigh only 0.6 g and were attached to the bird like a backpack.
With another newly developed transmitter, weighing only 1 g, the scientists could also make a synchronous record of the brain activity in the birds while they were singing in their natural environment. An antenna placed near the birds’ tree recorded up to eight of these signals in parallel. With the help of an external sound card and a laptop, the singing and the brain signals were synchronously recorded with millisecond precision. “The technology we have developed must withstand the extreme conditions of the Kalahari Savannah in northern South Africa”, says Susanne Hoffmann, a scientist in the Department of Behavioural Neurobiology. “The electronics for recording the signals were stored in a car. During the day, it got so hot that the laptop almost began to glow. But the recordings all worked well, even when the birds and their transmitters were caught in one of the few downpours”.

Brain activity of the duetting birds synchronizes
Lisa Trost, also a scientist in the department, says: “Fortunately, the procedure for fixing the implants for neuronal measurements on the heads of the birds did not take long. After complete recovery, the respective bird was quickly returned to the group and did not lose its social status. All birds sang in the tree immediately after their return”. The researchers recorded almost 650 duets. In many cases, the males began with the song and the partner joined in after some introductory syllables. The syllables between the duetting pair followed each other without delay and in perfect coordination. The coordination was so precise that analysis showed only a 0.25s delay between the duetting partners’ singing bouts.

The singing of songbirds is controlled by a network of brain nuclei, the vocal control system. In one of these nuclei, the HVC, the call of the partner bird triggers a change in neuronal activity in the bird that began singing. This, in turn, affects its own singing. The result is a precise synchronization of the brain activity of both birds. “The rhythmic duet of the individuals is achieved through sensory information that comes from the partner”, says Manfred Gahr, who led the study. The brains of the partners form a network that functions like an extended circuit to organize the temporal pattern for the duet. The researchers suspect that similar mechanisms are also responsible for coordinating movement during social interactions in humans (e.g. dancing with a partner).
“Until now, this kind of study has only been performed in the laboratory. Measuring the activity of nerve cells in the field using wireless transmitters is much less stressful for the birds,” says Susanne Hoffmann. “We hope this study has laid the foundation for the further development of neuroethology”.

Hoffmann S, Trost L, Voigt C, Leitner S, Lemazina A, Sagunsky H, Abels M, Kollmansperger S, Maat AT, Gahr M. (2019) Duets recorded in the wild reveal that interindividually coordinated motor control enables cooperative behavior. Nat Communications, 10, 2577.
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Hoffmann S, Trost L, Voigt C, Leitner S, Lemazina A, Sagunsky H, Abels M, Kollmansperger S, Maat AT, Gahr M. (2019) Duets recorded in the wild reveal that interindividually coordinated motor control enables cooperative behavior. Nat Communications, 10, 2577.
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The post Duets recorded in the wild reveal that interindividually coordinated motor control enables cooperative behavior. first appeared on Max Planck Neuroscience.

In female songbirds, brain areas responsible for song learning are usually smaller and have fewer neurons compared to males. However, in many species such as the blue-capped cordon bleu, females possess an elaborate song. Scientists from the Max Planck Institute for Ornithology in Seewiesen now found in this species pronounced sex differences in the brain already in juvenile birds, where females had up to 50% less neurons in the song control areas. However, this had no effect on the song learning process. Only when adult, females had developed a different song with shorter and simpler strophes than males.

In all songbirds investigated to date there are sex differences in those parts of the brain that are responsible for the learning and the production of song. These brain areas are smaller in females and they possess fewer neurons. This fact is often used as an explanation why females have simpler songs than males or do not sing at all. The neuroanatomical sex differences emerge during development and have a genetic basis or are due to the action of steroid hormones. For example, female song can be induced by the male sex hormone testosterone.

Nevertheless, there are species, in particular in the tropics, where males and females sing nearly similar songs. It is assumed that the song is important for pair bonding and year-round defense of a territory and food resources. Scientists headed by Manfred Gahr from the Max Planck Institute for Ornithology in Seewiesen have for the first time investigated the development of song and the underlying neuroanatomical changes in a species with female song. Male and female blue-capped cordon bleus that originate from East Africa, start their first vocalizations around the age of 30-40 days. The scientists analyzed different song traits during development in regular intervals and found sex differences only after the birds reached adulthood and were older than 250 days. At that time females suddenly started to sing shorter and simpler songs as their male peers of the same age.

In parallel the scientists investigated the birds’ neuroanatomical properties. Most remarkably, volume and neuron number of the song control regions HVC and RA were smaller in females compared to males from the first point of investigation at day 20 and persisted throughout the entire developmental period. “These anatomical sex differences are present already in a very early developmental stage and precede the sex differences in song behaviour”, says Manfred Gahr. However, this is not the only amazing result. Despite these different anatomical prerequisites there is a parallel brain development in both sexes. Although the song control centers are up to 55% smaller and have 30-50% fewer neurons, females develop a song comparable to that of males. At least for song learning, these sex differences do not seam to have a functional role.

Original Publication:
Lobato M, Vellema M, Gahr C, Leitao A, de Lima S, Geberzahn N and Gahr M
Mismatch in sexual dimorphism of developing song and song control system in blue-capped cordon-bleus, a songbird species with singing females and males.
2015 Front. Ecol. Evol. 3:117. Doi: 10.3389/fevo.2015.00117

The post In cordon bleus, song develops independently of sex differences in the brain first appeared on Max Planck Neuroscience.