(Inside Science) -- What is a concussion? The precise definition still eludes us in many ways. A concussion is a type of traumatic brain injury, and a good clinical definition of a concussion is a trauma-induced alteration in the level of neurologic functioning. But what does that mean exactly?

"In simple terms, a concussion is when a blow is sustained to the head that manifests itself in some form of consequence, whether that is a symptom that is precipitated, or whether it's an actual neurologic deficit that arises from that blow to the head," said David Okonkwo, clinical director at the UPMC Brain Trauma Research Center.

"That could be a direct injury -- in other words, they get hit in the head -- or it can be indirect, in that their body moves in such a way that the head is -- which is a mobile structure on the body -- the head moves around in some sort of shaking motion that disturbs the functioning of the brain. So, if there's any sort of trauma like that that then results in headache, changes in the way you're thinking or functioning, sensitivity to light and noise, etc., that can be defined as a concussion," said Mark Proctor, neurosurgeon-in-chief at Boston Children's Hospital.

Many people link concussions to a loss of consciousness, but Proctor said that's actually the minority of concussions.

"Ten or 15 years ago, even physicians thought a concussion was a loss of consciousness after a blow to the head. And now most physicians know that's not the case. You don't have to lose consciousness. And even most players and families know that that's not the case," said Proctor.

Today doctors like Proctor consider concussions to be functional injuries. They are not defined by what a doctor sees in a brain scan but rather by how someone is doing after suffering an injury to the brain.

"By and large, if you do a CT scan or an MRI scan, it's all going to look fine. So, the basic structure of the brain seems to be fine, at least on any external or obvious level. But there's a disturbance in the way the brain functions. So, the brain is sort of like a complex electrical circuitry, and the disruption caused by the concussion and the shaking of the brain temporarily alters that circuitry. In fact, if it -- if the imaging showed something, you'd say, 'Well, it's not a concussion. It's something else,'" said Proctor.

The good news is that while efforts to better understand, evaluate and treat concussions still have ways to go, they are already bearing fruit for the benefit of patients of all ages and backgrounds.

"So at this point in 2017, it is quite easy for someone who has sustained a concussion, whether it is by participating in a sport, whether it's by slipping and falling down the stairs while you're carrying the laundry to the basement, or whether it's just riding your bike around the neighborhood, we now have many avenues for people to engage with an expert in the field of concussion and undergo a proper evaluation," concluded Okonkwo.