"When there's a sufficient impact to the head, there is an immediate disruption of the brain's normal physiology," said Dr. Michael McCrea, professor of neurosurgery and neurology and director of brain injury research at the Medical College of Wisconsin, who has been studying concussion and traumatic brain injury for more than 15 years. "The brain is essentially sent temporarily into a state of disarray where the normal exchange of chemicals and neurotransmitters is significantly disrupted. The brain enters into a period of pretty severe energy crisis where that neuron can't perform in its normal fashion."
Symptoms produced from a concussion, he said, include abnormalities in memory and thinking abilities, balance problems, headaches and sensitivity to light, in addition to other kinds of symptoms.
Currently, said McCrea, the timetable for an athlete to return to the sport is between one and two weeks, but that can vary on a case-by-case basis.
"With rest, the brain returns to a normal, steady state and the symptoms resolve over a period of days in most cases," he said. "One athlete might take five days; another athlete might take 20 days."
What's no longer debatable, he said, is whether or not an athlete who has sustained a concussion should continue to participate.
If a second concussion is sustained before recovery, said Dr. William Cullinan, dean of the Marquette University College of Health Sciences, that waiting period stretches to six weeks.
And while the science of understanding concussions and traumatic brain injury has come a long way, there's still a long way to go.
Cullinan said there's still much to be understood when it comes to the consequences of multiple concussions, sub concussive impact, CTE (Chronic traumatic encephalopathy), and in concussions sustained by young people whose brains are still developing.
Nevertheless, the understanding of concussions has "come a long way from asking how many fingers you're holding up," said Cullinan.