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Specialised nerve cells in auditory brainstem allow 'cocktail party listening'
21 May 2014
Nerve cells in the auditory brainstem are specialised to be able to pick out sounds at different frequencies in an efficient manner reports a new study published in the journal PNAS Plus.
'Cocktail party listening' - the ability to pick out specific sounds
against a background of noise, such as conversations in a party, has been
recognized for some time.
Our hearing system uses several cues to determine the location of a sound, including comparing the sounds arriving at each ear. The importance of these cues varies with sound frequency.
In this study Professor David McAlpine (UCL Ear Institute) showed
that nerve cells in the auditory brainstem are specialised to be able to pick
out sounds at different frequencies in an efficient manner.
He explains, "Through in vitro recordings we show that the biophysical properties of brainstem neurons vary with their presumed sound frequency tuning. Using neural modeling we demonstrate that the cell properties are well suited to extract spatial cues from natural sounds, including in background noise."
Neurons receiving low sound-frequency information from each ear have fast electric resonances, making them suited to extract small ITDs in the order of a few tens of microseconds, even when the background noise is more intense than the sounds themselves. In contrast, neurons receiving input from higher sound-frequencies use this information relatively slowly over time, maximizing their ability to compare the sound level at each ear, but at the expense of following rapid changes in the sound.
Through in vitro recordings we show that the biophysical properties of brainstem neurons vary with their presumed sound frequency tuning.
Professor David McAlpine
These central properties of binaural neurons provide an explanation for the listening abilities of many species, including humans, and demonstrate the importance of low-frequency hearing in noisy listening situations.
They also provide a potential explanation for why users of cochlear implants - electrical devices that stimulate directly the nerves of the inner ear - have difficulty listening background noise, since the electronic signals conveyed by these devices are largely confined to the higher sound-frequencies.