Scientists have devised a simple test that can accurately assess whether someone has suffered concussion.
The test, which works with 90 per cent accuracy, works by monitoring how the injured person responds to sound.
An electrical sensor attached to the scalp monitors how closely the person's brainwaves mirror the soundwaves.
If someone is concussed, the signal is not picked up so clearly.
The test is necessary as concussion is notoriously difficult to detect following a blow to the head – and is a particular problem during sports.
Whether a sudden impact has caused brain injury – and further investigation is necessary – or is not serious is hard to assess.
This is because damage to the brain is not necessarily reflected by the severity of the blow.
And medical staff largely rely on the injured person accurately reporting their symptoms.
But suffering a concussion could lead to serious consequences if undiagnosed – and expose a concussed person to a risk of even greater injury.
Researchers at Northwestern University said that the study relied on the finding that a concussed person has a 'compromised ability to make sense of sound'.
Lead author Nina Kraus said: 'This biomarker could take the guesswork out of concussion diagnosis and management.
'Our hope is this discovery will enable clinicians, parents and coaches to better manage athlete health, because playing sports is one of the best things you can do.'
By observing research subjects' brain activity as they were exposed to auditory stimuli, Kraus and her team discovered a distinct pattern in the auditory response of children who suffered concussions compared to children who had not.
Using three simple sensors placed on children's heads, the researchers measured the brain's frequency following response – the brain's automatic electrical reaction to sound.
They were able to successfully identify 90 percent of children with concussions and 95 percent of children in the control group who did not have concussions.
Children who sustained concussions had response to the sound that was 35 percent smaller than the unconcussed children.
As the children recovered from their head injuries, their ability to process pitch returned to normal.
Professor Kraus said: 'Making sense of sound requires the brain to perform some of the most computationally complex jobs it is capable of, which is why it is not surprising that a blow to the head would disrupt this delicate machinery.'
She added: 'This isn't a global disruption to sound processing, it's more like turning down a single knob on a mixing board.'
The brain's response to sound is a good indicator of overall brain health as the auditory system is in the middle of the brain and connected closely to our cognitive, sensory and emotional systems.
The study, published in Scientific Reports, was based on 40 children.
The researchers said their objective is to produce a portable device that is capable of detecting concussion.
Professor Kraus said: 'With this new biomarker, we are measuring the brain's default state for processing sound and how that has changed as a result of a head injury.
'This is something patients cannot misreport, you cannot fake it or will your brain to perform better or worse.'