Something strange happens to mice when they’re shut away in the dark for an extended period of time: they develop a sort of super-hearing ability, becoming more sensitive to the sounds around them.
This kind of compensatory sensory effect has been observed plenty of times before, including in humans, but a new study gives us a more detailed understanding of what might be happening inside the brain.
In the mice kept in darkness during the experiment, the brain’s neurons actually shifted in the way they interacted with each other, tweaking sensitivity to different audio frequencies, and showing a sort of flexibility that has been thought to be characteristic of young, developing brains.
“This study reinforces what we are learning about how manipulating vision can have a significant effect on the ability of an animal to hear long after the window for auditory learning was thought to have closed,” says biologist Patrick Kanold, from the University of Maryland.
It’s important not to place too much weight on a study that involved testing just 15 mice, 6 of whom were kept in the dark for seven days, with the other 9 left to live in a normal cycle of day and night.
But if these same neural network shifts are found to be happening in humans too, then it could give us new treatment options; for example, such insights into brain wiring could help us to understand how people with hearing impairments can better adapt to a new hearing aid.
This sort of sensory manipulation – restricting one sense to affect another – is known as cross-modal learning, and scientists think that it could give us ways to retune our brains for all kinds of purposes, long after the optimum learning window of childhood has passed. The problem is, we still don’t understand very much about it.
Kanold and his colleagues had previously established that limiting what adult mice could see would in some ways boost what they could hear. In this case they went into more detail in terms of analysing specific neuron groups and testing the mice with 17 different sound tones across multiple frequencies.
The scientists were surprised to find the brains of the mice reallocating resources to different frequencies of sound to hear them better. A greater proportion of neurons were assigned to listening for high- and low-frequency sounds, with a smaller proportion used to detect the mid-range.
As enlightening as this is, there’s plenty more still to explore: the researchers want to run further experiments to find out exactly what part of the soundscape the mice are listening to while they’re in the darkness.
“We don’t know why we are seeing these patterns,” says Kanold. “We speculate that it may have to do with what the mice are paying attention to while they are in the dark.”
“Maybe they pay attention to the noises or voices from the other mice, or maybe they’re paying more attention to the footsteps they are making.”
The research has been published in eNeuro.