Researchers at Cold Spring Harbor Laboratory (CSHL) have found how humans are able to focus on one particular sound among many in noisy environments such as offices or cocktail parties.
The researchers have reported new findings about how the mammalian brain interprets and fashions representations of sound.
Neurons in the brain's auditory cortex interpret incoming sound signals and send them to the rest of the nervous system, in the brain and spinal cord.
Using rats, the researchers found that a very small minority of available auditory neurons react strongly when exposed to any specific sound.
"This finding challenges the standard model of sound representations in the auditory cortex, which predicts that neural representations of stimuli often engage a large fraction of neurons," said Anthony Zador, Ph.D., CSHL professor and co- author of the study.
For the study, the researchers used a new technique called 'in vivo cell-attached patch clamp recording' which measures the reaction of individual neurons.
This recording method samples neurons in a fair and unbiased way, unlike traditional approaches, which favoured the largest and most active neurons.
With the help of this method, the researchers found that only 5 percent of neurons in the auditory cortex had a 'high firing rate' when receiving a range of sounds of varying length, frequency, and volume. The test included white noise and natural animal sounds.
The aim of the study was to quantify the relative contributions of different sub-populations of neurons in response to the range of sounds.
The researchers found that half of the neurons measured in the reported experiments showed no reaction at all to incoming stimuli. They hypothesize that each neuron in the auditory cortex may have an 'optimal stimulus' to which it is particularly sensitised.
"Your entire sensory apparatus is there to make successful representations of the outside world. Sparse representations may make sensory stimuli easier to recognize and remember," said Dr. Zador, who is director of the CSHL Swartz Center for Computational Neuroscience.
Identifying the brain's ability to differentiate 'optimal stimuli' could help scientists find ways to improve how sounds are learned.
This is the first evidence of a correlation between sparse representations and hearing.
"The goal of sensory processing is to take a signal, like a sound or a vision, from your environment and use it to drive behaviour. The brain needs to recognize and learn about these inputs in order to survive," said Dr. Zador.
The study is published in the journal Public Library of Science: Biology.