As it turned out, even though all the sounds had short-term neurological effects, not one of them had a lasting impact. Yet to her great surprise, Kirste found that two hours of silence per day prompted cell development in the hippocampus, the brain region related to the formation of memory, involving the senses. This was deeply puzzling: The total absence of input was having a more pronounced effect than any sort of input tested.

Here’s how Kirste made sense of the results. She knew that “environmental enrichment,” like the introduction of toys or fellow mice, encouraged the development of neurons because they challenged the brains of mice. Perhaps the total absence of sound may have been so artificial, she reasoned—so alarming, even—that it prompted a higher level of sensitivity or alertness in the mice. Neurogenesis could be an adaptive response to uncanny quiet.

The growth of new cells in the brain doesn’t always have health benefits. But in this case, Kirste says that the cells seemed to become functioning neurons. “We saw that silence is really helping the new generated cells to differentiate into neurons, and integrate into the system.”

While Kirste emphasizes that her findings are preliminary, she wonders if this effect could have unexpected applications. Conditions like dementia and depression have been associated with decreasing rates of neurogenesis in the hippocampus. If a link between silence and neurogenesis could be established in humans, she says, perhaps neurologists could find a therapeutic use for silence.

Does silence while sleeping count?

Does silence while reading count?

Does silence while on a computer or tablet count?

While it’s clear that external silence can have tangible benefits, scientists are discovering that under the hoods of our skulls “there isn’t really such a thing as silence,” says Robert Zatorre, an expert on the neurology of sound. “In the absence of sound, the brain often tends to produce internal representations of sound.”

Imagine, for example, you’re listening to Simon and Garfunkel’s “The Sound of Silence,” when the radio abruptly cuts out. Neurologists have found that if you know the song well, your brain’s auditory cortex remains active, as if the music is still playing. “What you’re ‘hearing’ is not being generated by the outside world,” says David Kraemer, who’s conducted these types of experiments in his Dartmouth College laboratory. “You’re retrieving a memory.” Sounds aren’t always responsible for sensations—sometimes our subjective sensations are responsible for the illusion of sound.

This is a reminder of the brain’s imaginative power: On the blank sensory slate of silence, the mind can conduct its own symphonies. But it’s also a reminder that even in the absence of a sensory input like sound, the brain remains active and dynamic.

Well that's cool. And a reminder to activate our imagination more.