Concussion is a condition that is often misunderstood. In most cases it does not involve a loss of consciousness. It is often mistakenly referred to as a bruise to the brain, but bruising and bleeding are actually associated with other, more serious types of traumatic brain injury (TBI). Rather, a concussion is a complex cascade of chemical changes that occur at the cellular level when the brain moves violently within the skull.

Though scientists cannot study living human brains undergoing concussion, and cannot see what is happening with a CT scan (computerized tomography) or MRI (magnetic resonance imaging), they have been able to observe the brains of rats during and after an impact.

"The brain is made up of different densities of tissue," said Dr. Kendra Bryant of Neuropsychology and Concussion Management Associates of Rockport. "As the brain is jostled within the skull, there is pulling and even tearing at the margins of these different densities."

Think of the brain as an intricately folded and delicately-wired Jello-mold. If someone gets hit hard enough, the gelatin-like globe can stretch and deform with the force of the impact. It may bounce off the solid wall of the skull, or areas of different densities may move with different velocities.

After impact, Bryant said, neurons release chemicals, setting off a cascade of disruptions to metabolic processes that results in an energy crisis at a time when the brain needs a tremendous amount of energy to heal. One step of the process involves calcium ions entering neurons and disrupting ATP (energy) production.

All these changes can bring about an array of symptoms, including fatigue, sleep problems, headaches, visual problems, dizziness, nausea, irritability, anxiety, sadness, slowed thinking, concentration problems and memory impairment. The effects of these changes are generally short-lived, but can persist for weeks or months in some cases.

One possible reason for longer-lasting symptoms is something scientists have observed using new imaging techniques: twisting and stretching causes holes to form in the brain's white matter.

When describing white matter, Bryant used the image of an electrical cord. Each cell of the brain and spinal cord has an axon like an electrical wire that allows it to communicate with other cells.

"We have big bundles of axons in our brain and down our spinal cord, which are responsible for pretty much everything we do," she said.

Axons are coated with a white insulating material called myelin, similar to the plastic around an electrical cord, which allows signals to travel along them more quickly. More important functions have more insulating material.

"When stretching and twisting occurs, small holes can form in the 'plastic coating,' meaning the information won't transmit as smoothly because it is less insulated," Bryant said. "[In a concussion] you do not lose a function completely and permanently, for example the ability to talk, but may have less efficiency, speed, or agility in that function.”

Long-term effects uncertain

There is much about the human brain that is still a mystery, and though scientists can tell you what is happening during concussion, what it means long term is still under debate.

Concerns about potential long-term damage arose when chronic traumatic encephalopathy, or CTE, was found after death in the brains of many former pro football players who had developed dementia-like symptoms in middle age. Recently CTE, evidenced by a buildup of the protein "tau" in the brain, was found in the brain of a 19-year-old former football player who committed suicide. The National Football League agreed to settle a class-action law suit by paying former players who develop Alzheimer's, Parkinson's and similar diseases, and funding research into the long-term effects of concussions.

Moriah Grant of Waldo County General Hospital's concussion management program said keeping up with current research involves "reading and analyzing at the same time because there’s nothing to grasp yet; it is such an early thing, there is no data yet.”

The question of why some people who have had concussions or a lot of battering in sports show impairment in middle age while others do not is still unanswered. Many small studies, usually involving athletes, are being reported now.

One recent study published in the journal Neurology showed that of 86 subjects, those with mild TBIs had a 25-percent lower score than healthy subjects in tests of language and memory within one week of the injury, and after a year, some had not returned to normal. Another published in that journal of 42 former NFL players ages 41 to 65 found those who started playing football before the age of 12 performed “significantly worse” on cognitive tests.

At the December 2014 Radiological Society of North America annual meeting, a study was presented of 24 football players between the ages of 16 and 18 that found changes similar to mild TBIs in the players' brains after one season, even if they weren’t concussed. Another study presented showed that, of 80 college football and hockey players tested, the more the brain changed over a season, the worse they did on memory and cognitive tests.

One study found a disruption of the blood-brain barrier in athletes who had experienced multiple impacts in a game. A brain protein called S100B was found to spike in athletes who had multiple impacts.

As these and other small studies are beginning to paint a picture of potential effects of impacts on the brain, many doctors and scientists continue to assert that health benefits of playing impact sports outweigh the risks. Dr. Antonio Belli of University of Birmingham (U.K.) says that the brain changes that occur are innocuous in most people, but more significant for people with prior head injuries. Some say long-term brain damage is more likely to be the result of multiple concussions and impacts, or the "dose effect" of repetitive blows as experienced in professional football.

Grant stresses that it is not safe to risk a second concussion until no symptoms of the previous one return under any physical or mental challenge. "This means, for example, being able to take the SATs, work a hard day at work, and run a marathon — without symptoms," she said.