Scientists at University of Rochester in New York have found that sex hormone oestrogen controls how the brain processes sounds.
This is the first time that any study has shown that a sex hormone can directly affect auditory function.
The researchers say that their study points toward the possibility that oestrogen controls other types of sensory processing as well.
According to them, understanding how oestrogen changes the brain's response to sound may open the door to new ways of treating hearing deficiencies.
"We've discovered estrogen doing something totally unexpected. We show that estrogen plays a central role in how the brain extracts and interprets auditory information. It does this on a scale of milliseconds in neurons, as opposed to days, months or even years in which estrogen is more commonly known to affect an organism," says Raphael Pinaud, assistant professor of brain and cognitive sciences at the University of Rochester and lead author of the study.
The researcher has revealed that past studies have already hinted at a connection between oestrogen and hearing in women who have its low levels, something that often occurs after menopause.
He, however, insists that no one actually knew that oestrogen plays such a direct role in determining auditory functions in the brain.
"Now it is clear that estrogen is a key molecule carrying brain signals, and that the right balance of hormone levels in men and women is important for reasons beyond its role as a sex hormone," says Pinaud.
Working in collaboration with Assistant Professor Liisa Tremere and postdoctoral fellow Jin Jeong, Pinaud showed that increasing oestrogen levels in brain regions, which process auditory information, caused heightened sensitivity of sound-processing neurons, which encoded more complex and subtle features of the sound stimulus.
He reveals that when the actions of oestrogen were blocked, or brain cells were prevented from producing the hormone within auditory centres, the signalling that is necessary for the brain to process sounds shut down.
His team have also shown that oestrogen is required to activate genes that instruct the brain to lay down memories of those sounds.
"It turns out that estrogen plays a dual role. It modulates the gain of auditory neurons instantaneously, and it initiates cellular processes that activate genes that are involved in learning and memory formation," says Pinaud.
Pinaud and his colleagues made these findings while studying how oestrogen may help change neuronal circuits to form memories of familiar songs in a type of bird typically used to understand the biology of vocal communication.
"Based on our findings we must now see estrogen as a central regulator of hearing. It both determines how carefully a sound must be processed, and activates intracellular processes that occur deep within the cell to form memories of sound experiences," he says.
The researchers will continue their work studies to find out how neurons adapt their functionality when encountering new sensory information, and how these changes may ultimately enable the formation of memories.
They also will continue exploring the specific mechanisms by which estrogen might impact these processes.
"While we are currently conducting further experiments to confirm it, we believe that our findings extrapolate to other sensory systems and vertebrate species," says Pinaud. "If this is the case, we are on the way to showing that estrogen is a key molecule for processing information from all the senses."
The study has been published in The Journal of Neuroscience.