Cool brains slow the tempo

The ‘clock’ that orchestrates the complex vocal behavior in songbirds has been identified by researchers in the USA, who report their findings in this week’s edition of Nature.

Complex motor behaviors, such as human speech, dance or birdsong, require precisely coordinated movement of many different muscles on many different timescales. Despite having identified the brain areas and the patterns of neuronal firing required for this, scientists had puzzled over the specific brain circuits involved in the timing of such complex behavioral sequences.

By working from the fact that the speed of brain processes is strongly dependent on temperature, Michael Long and Michale Fee at the Massachusetts Institute of Technology were able to pinpoint an area of the brain known as the ‘premotor nucleus HVC’ (formerly known as the high vocal center) as the controller of song timing in zebra finches.

The researchers produced localized mild heating or cooling in different brain areas and looked for changes in the overall speed of songs. They found that reducing the temperature in the HVC of the brain slows the zebra finch’s song speed across all timescales by up to 45%. Cooling other important song-related brain areas, however, has no effect of timing.

“Cooling HVC … stretches the temporal fabric of the song, slowing tempo but leaving acoustic features such as pitch largely unchanged,” note Chris Glaze of the University of Pennsylvania, USA, and Todd Troyer of the University of Texas San Antonio, USA, commenting in a related News and Views article. “Moreover, the degree of cooling determined the amount of slowing, allowing the authors to effectively ‘dial in’ a desired tempo,” they write.

Long and Fee’s findings suggest that not only is the HVC the location of the clock that regulates the timing of birdsong, but this area of the brain is also important for the timing of other complex behaviors. They conclude that their experimental approach — which Glaze and Troyer describe as “remarkable” — “may be broadly useful in localizing specialized brain circuits that control the timing of other behaviors.”