Where did the "sense of rhythm" come from?

Many of our bodily functions, such as walking, breathing, and chewing, are controlled by brain circuits called the central oscillator, which produce rhythmic firing patterns to regulate these behaviors

Neuroscientists at the Massachusetts Institute of Technology (MIT) have now discovered a neuronal property and mechanism in these circuits: an oscillator that controls the rhythmic back-and-forth swing of mouse tactile tentacles

The MIT team found that swing oscillators consist of a cluster of inhibitory neurons in the brainstem that burst rhythmically during swings

"We have molecularly, electrophysiologically, functionally and mechanistically defined mammalian oscillators," said Fan Wang, MIT professor of brain and cognitive sciences and a member of MIT's McGovern Institute for Brain Research

Wang is the senior author of the study, which was published today in the journal Nature

rhythmic behavior

Most studies that definitively identify central oscillator circuits have been done in invertebrates

Characterization of oscillators in mammals, especially awake behaving animals, has proven to be very challenging

"There are no detailed studies of awake behaving animals where one can record from molecular recognition oscillator cells and manipulate them in a precise way

Shaking is a prominent rhythmic exploratory behavior in many mammals that uses tentacles to detect objects and perceive texture

To find the location of the wiggling oscillator, the researchers traced from the motor neurons that innervate the whisker muscles

The researchers then found that about half of these vIRt neurons expressed a protein called parvalbumin, a subset of cells that drives the rhythmic movements of the whiskers

Next, the researchers recorded the electrical activity of parvalbumin-expressing vIRt neurons in the brainstem of awake mice, a technically challenging task, and found that these neurons indeed burst into activity only during whisker contractions

"It was a super satisfying and rewarding moment to see that these cells were indeed oscillator cells, because they were firing rhythmically, they were firing during the contraction phase, and they were inhibitory neurons," Wang said

"New Principles"

The oscillatory burst pattern of vIRt cells was initiated at the onset of agitation

This type of network, known as a repetitive inhibitory network, differs from the type of oscillators seen in the stomach neurons of lobsters, where neurons essentially generate their own rhythms

"Now we have discovered a mammalian network oscillator composed of all inhibitory neurons," Wang said

The MIT scientists also collaborated with a team of theorists led by David Golomb of Ben-Gurion University in Israel and David Kleinfeld of the University of California, San Diego
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The theorists created a detailed computational model outlining how to control the stirring, which matched all the experimental data well
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A paper describing the model appears in an upcoming issue of Neuron
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Wang's lab now plans to study other types of oscillatory circuits in mice, including those that control chewing and licking
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"We were very excited to discover these oscillators of feeding behavior and compare and contrast them with stirring oscillators, since they are all in the brainstem, and we wondered if there were some common themes, or if there were many different ways to generate oscillator
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This research was funded by the National Institutes of Health
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