Boffins discover the sound of silence

A team of Oregon boffins has identified a part of the brain that deals specifically with shutting off sound processing.

They say a bit of silence is vital for hearing and for understanding speech.

Writing in the journal Neuron, which we get for the “spot the brain cell” competition the discovery flies in the face of a long-held assumption that the signalling of a sound’s appearance and its subsequent disappearance are both handled by the same neural pathway.

The new finding, which supports an emerging theory that a separate set of synapses is responsible, could lead to new, distinctly targeted therapies such as improved hearing devices.

Michael Wehr, a professor of psychology and member of the UO Institute of Neuroscience said that it looks like there is a whole separate channel that goes all the way from the ear up to the brain that is specialized to process sound offsets.

The two channels come together in a brain region called the auditory cortex, situated in the temporal lobe.

Wehr, Ben Scholl, and Xiang Gao monitored the activity of neurons and their connecting synapses as rats were exposed to millisecond bursts of tones, looking at the responses to both the start and end of a sound. They tested varying lengths and frequencies of sounds in a series of experiments.

One set of synapses responded “very strongly at the onset of sounds,” but a different set of synapses responded to the sudden disappearance of sounds.

Being able to perceive when sound stops is very important for speech processing. This discovery answers the question about how the brain find the boundaries between the different parts of words, particularly when you are in a noisy pub.