February 28, 2013
Songbird Brain Activity Sheds Light On Complex Human Behavior
redOrbit Staff & Wire Reports - Your Universe Online
New research involving songbirds may help explain how the human brain is organized to govern skilled performance, a finding that could lead to new ways of understanding human speech production and other complex behaviors.
The researchers found that whenever a bird sings, some of the neurons in its brain prepare to make the next sounds while others are synchronized with the current notes. This coordination of physical actions and brain activity is required to produce complex movements, the scientists concluded in an article about their work published in the current issue of the journal Nature.
Neuroscientist Daniel Margoliash and colleagues showed that birds' physical movements are actually 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 University of Chicago.
"This work provides new insight into how the physics of producing vocal signals are represented in the brain to control vocalizations," said speech expert Howard Nusbaum, a professor of psychology at UChicago.
By decoding the neural representation of communication, the research may shed light on speech problems such as stuttering or aphasia, a disorder following a stroke, he added.
The research also provides a unique view into how the brain and body conduct other types 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.”
"With all this complexity, it has been difficult to determine which of the many variables that describe movements are the ones that are represented in the brain and used to control movements.”
Margoliash, a pioneer in the study of brain function in birds, said it is challenging to find a natural framework with which to analyze the activity of single neurons.
“The bird study provided us a perfect opportunity," he said.
Margoliash´s previous work includes research into how learning occurs when a bird sleeps, and how it recalls singing a song.
The researchers studied zebra finches while the birds sang and slept (when songs were broadcast through a speaker). Next, they recorded the activity of single neurons through tiny wires connected to the birds' brains.
Gabriel Mindlin, professor of physics at the University of Buenos Aires, and his students created a mathematical model of the mechanics of the movement of the syrinx, the avian vocal organ. They used that information to track the connections between brain responses and the physical actions needed to produce a song.
The researchers reduced the description of a song to only two variables: the pressure pushing air through the syrinx and the tension of the vibrating membranes of the syrinx, which are needed to produce the song.
They also compared the timing predicted by the model with the timing of responses of the neurons in the bird's "song system,” revealing how activity at higher levels of the brain tracks basic motor functions.
The researchers avoided a problem previous scholars had encountered. In the past, investigators did not know how to relate song with the variables of pressure and tension, and so they had an incomplete understanding of how neurons controlled song, Margoliash explained. For example, a previous theory of song control suggested that a clock in the brain that runs independent of the song governs these complex movements.
By looking at the physiological variables that the bird uses to control singing, the researchers were able to find something others had not noticed before: the precise timing between the firing of the neuron and the action connected with it.
"One fascinating observation we made really surprised us: that the forebrain neurons fire precisely at the time a sound transition is being produced," Margoliash said.
"But it takes far too much time for the activity in the forebrain to influence the bird's sound box in the periphery.”
The neurons that the team investigated are tracking and encoding particular moments in song but are not directly controlling them.
"Lower levels of the brain are controlling the sound output, but the timing of these neurons suggest that they are helping to evaluate feedback from the produced sound."
Similar feedback plays a vital role in coordinating human speech, and in the skilled performance of athletes and musicians.
The researchers said the current study provides, for the first time, a mathematical description that matches brain activity for highly skilled behavior.
Margoliash´s team included Ana Amador, a post-doctoral researcher at UChicago, and University of Buenos Aires scholars Yonatan Sanz Perl and Gabriel Mindlin. The four are co-authors of the Nature paper, entitled "Elementary Gesture Dynamics are Encoded by Song Premotor Cortical Neurons.”