Brain neurons ‘trigger chain reaction like a cascade of falling dominos’

LONDON - Scientists at MIT have identified a “chain reaction” of brain activity that appears to control the timing of a bird song, saying that neurons in brain fire a chain reaction, much a like a cascade of falling dominos.

Michale Fee and colleagues had previously shown that the tempo of the song is controlled by a brain area known as HVC.

Different neurons fire at different times, so the activity of these neurons represents a ‘time stamp’ that causes the correct instructions to be sent to the vocal organs at each instant within the song.

As to how the timing is perfect in each HVC neuron, Fee believes the most plausible idea is the “synfire chain” model, in which neurons fire in a chain reaction - each one triggering the next in the sequence, like a cascade of falling dominos.

In a technical tour-de-force, they developed a method in which these recordings could be made while the bird was freely moving around his cage and engage in natural behaviors such as singing.

Their results support the chain of dominoes model. When individual HVC neurons fire, they do so suddenly, as if hit by the preceding domino.

There was no prior build-up of activity; instead, each neuron remained silent until its turn came to fire, at which point it showed a sudden burst of activity.

In further experiments, the authors showed that this burst of activity is triggered suddenly by an all-or-none influx of calcium through specialized membrane channels that open in response to this excitatory input.

The MIT researchers also showed that the timing of neural bursts in HVC neurons is not easily disturbed by small electrical perturbations.

“We predict that similar mechanisms probably exist in other brains, including our own,” said Fee.

The study appears in Nature. (ANI)