Concussion Fast Facts

A concussion is a type of traumatic brain injury (TBI) in which the brain is injured by an impact or a sudden change in movement.

Each year in the United States, sports- and recreation-related activities cause between 1.7 and 3 million concussions.

Half of all concussions are not reported, and they go untreated.

About 300,000 concussions annually are attributable to football-related injuries.

Contrary to widely held beliefs, concussions don’t necessarily cause a loss of consciousness.

Most concussions, if treated quickly and correctly, do not cause long-term harm.

United Brain Association

It’s been a common misconception that a concussion causes a loss of consciousness, but in fact, most people do not blackout when the concussion occurs.

What is a Concussion?

A concussion is a type of brain injury resulting in immediate, temporary loss of some brain functions. A concussion is usually caused by an impact or a blow to the head, but it can also happen when a sudden change of motion causes the brain to move inside the skull. The impact or motion damages brain tissue; the damage results in symptoms that can begin immediately or may take up to a day to appear.

It’s been a common misconception that a concussion causes a loss of consciousness, but in fact, most people do not blackout when the concussion occurs. Concussions often harm memory, balance, coordination, reflexes, judgment, and speech, and the person may have trouble remembering what happened in the time immediately surrounding the injury. These symptoms often present themselves directly after the injury, but they may take some time to manifest, making quick evaluation and treatment necessary even when a head injury seems to be minor.

A large majority of concussions do not cause lasting damage to the brain, but multiple concussions can cause cumulative damage that leads to long-term problems. A second concussion that occurs soon after an initial concussion can be especially dangerous.

What Causes A Concussion?

Common causes of concussion include sports injuries, blows to the head, falls, and car accidents. The impact or violent shaking of the head that these events produce causes the brain to move, twist, or rotate inside the skull.  The brain may even move so much that it strikes the inside of the skull. This movement can cause bruising of brain tissue, but damage that usually causes concussion symptoms is a more subtle result of chemical changes in the brain at the cellular level.

Doctors and scientists do not entirely understand the biochemical changes that produce concussion symptoms. The fact that the symptoms are usually temporary leads scientists to believe that the chemical changes make brain cells behave incorrectly without actually killing the cells.

The chemical changes are sometimes called a “neurometabolic cascade.” The process of this “cascade” is complicated, but scientists think the injury causes the brain’s nerve cells (neurons) to enter a state in which they can’t communicate effectively with other neurons, leading to the symptoms of a concussion.

Given time and rest, the neurons will usually emerge from this dysfunctional state and begin to work correctly again. However, when the neurons are in an abnormal state, they are especially vulnerable to stress. They may die or be permanently damaged if reinjured before they’ve had a chance to recover. That’s why a second head injury that’s incurred soon after a concussion can be so serious.

Are Concussions Hereditary?

Since injuries and external physical events cause concussions, the likelihood of suffering a concussion isn’t linked to family history. There is a possibility, however, that the brain’s vulnerability to the effects of a concussion and its ability to recover could be, in some way, linked to genetics.

Several scientific studies have looked at the role of a gene called the apolipoprotein E gene in the brain’s response to traumatic brain injuries. This gene helps to produce a protein that seems to be involved in the maintenance and repair of neurons, and it may play a role in a brain’s ability to recover from an injury. Although the genetic mechanism involved is not yet completely understood, this or another gene (or genes) may make brain injuries more or less severe in specific individuals.

How Is A Concussion Detected?

Concussions often go undiagnosed because the injuries that cause them may seem minor, and the immediate symptoms might not seem severe. However, early detection of a concussion is crucial to prevent further injury and possible long-term damage. It’s important to be alert for both immediate symptoms and those symptoms that might emerge sometime after the initial injury.

Common immediate symptoms of a concussion include:

  • Headache
  • Confusion or mental fogginess
  • Dizziness or problems with balance
  • Loss of memory of the events surrounding the injury
  • Brief loss of consciousness (although this doesn’t happen with most concussions)
  • Slurred speech
  • Nausea or vomiting
  • Light sensitivity or vision disturbances
  • Fatigue

Symptoms of a concussion that can show up hours or days after the initial injury include:

  • Increased difficulty concentrating
  • More pronounced memory loss
  • Disruption in other senses, including hearing, taste, and smell
  • Difficulty sleeping
  • Personality shifts or increased irritability

In small children who aren’t able to express themselves verbally, warning signs of a concussion can include:

  • Changes in eating or sleeping behavior
  • Walking or balance difficulties
  • Irritability or unusual crying
  • Apparent fatigue or loss of interest in playing

How Is A Concussion Diagnosed?

Doctors will take several steps in attempting to diagnose a concussion. The diagnostic steps will begin with tests to see if concussion symptoms are present, and if these tests are positive or the symptoms are serious, further testing may be recommended.

  • Neurological exam. A doctor will perform an in-office exam that tests the patient’s neurological function. This exam will include tests of reflexes, balance, strength, coordination, vision, and hearing. The exam may also include tests of memory, concentration, and cognition.
  • Imaging tests. In cases where symptoms such as headache or vomiting are severe or when symptoms seem to worsen, a doctor may want to perform imaging tests to rule out a more severe brain injury that has caused bleeding or swelling in the brain.
  • Hospitalization and observation. A doctor may recommend hospitalization or in-home observation, often for 24 hours, to ensure that symptoms are not changing or getting worse.

How Is A Concussion Treated?

There is currently no treatment that will reverse the biochemical effects of a concussion in the brain. In most cases, the effects resolve on their own, given enough time and protection from further damage. Because of that, the treatment prescribed for concussion is almost always rest and protection from further injury. A doctor will usually suggest that the patient stay away from activities, such as physical or mental exertion, that could make symptoms worse.

The treatment can also include shortened work or school days, breaks from assignments and mentally complex tasks, and avoidance of technology utilizing display screens, such as TV, computers, and phones.

To treat headaches, a doctor will usually suggest over-the-counter pain relievers containing acetaminophen because concussion-related headaches often don’t respond well to more potent prescription painkillers. Pain relievers containing ibuprofen or aspirin may increase the risk of bleeding and are generally not recommended in the case of head injuries.

How Does A Concussion Progress?

The significant danger of concussions is the severe, lasting, and sometimes fatal damage done by repeated concussions or a head injury suffered when the patient is still recovering from a prior concussion. When these recurrent injuries happen, the results can be deadly.

Post-concussion syndrome (PCS) occurs in about 15% of people who suffer concussions. This syndrome’s symptoms can continue for weeks or months after the initial injury, and a diagnosis is usually made when symptoms last longer than three months after the injury.

Symptoms include:

  • Headache
  • Dizziness
  • Light or noise sensitivity
  • Sleep disruption
  • Ringing ears
  • Anxiety or depression
  • Mood swings
  • Aggression
  • Memory problems
  • Concentration problems
  • Cognition problems

Patients suffering from PCS should avoid sports or activities that bring an increased danger of further injury.

Second-impact syndrome (SIS) is a severe, often fatal condition that occurs when someone suffering from a concussion is subjected to a second brain injury. SIS results in brain swelling that can very quickly cause long-term brain damage or death. SIS’s cause is not fully understood, but it’s thought that brain cells have a limited ability to control blood flow into brain tissue during recovery from concussion, causing them to be vulnerable to bloodflow-related swelling.

SIS can happen when an injury is suffered even weeks after the initial concussion, and even a minor impact to the head during the vulnerable period can result in SIS.

How Are Concussions Prevented?

The key to preventing concussions is avoiding situations that put you at risk of a head injury.

  • Always wear properly-fitted protective headgear that has been officially certified by the American Society for Testing and Materials (ASTM) when participating in any sport or recreational activity that carries a risk of head injury.
  • Do not let young children play sports unsupervised.
  • Follow all safety rules and procedures while participating in sports or recreational activities.
  • Always wear a seat belt and proper restraints in cars and motor vehicles.
  • Always follow your doctor’s recommendations and treatment plan after suffering a head injury, and don’t resume your regular activities until your professional healthcare provider has cleared you to do so.

Concussion Caregiver Tips

Caregivers can help concussion sufferers by ensuring the recovery process goes smoothly and supporting the doctor’s treatment plan to lessen the severity of symptoms and prevent further injury.

  • Make sure the sufferer can get plenty of rest. Provide a quiet, stress-free place to rest, and avoid situations that cause lots of noise or activity in the home during recovery.
  • Parents of children who’ve had a concussion should enforce a recovery-friendly sleep schedule.
  • Communicate with the doctor or healthcare provider to understand what to look for in terms of symptoms and improvement while caring for the sufferer.
  • Communicate with other people in the sufferer’s life–family members, work colleagues, teachers, coaches, etc.–to be sure that everyone knows the recovery plan and accommodations needed to speed the sufferer’s recovery.

Many people who have had a concussion also suffer from other brain and mental health-related issues, a situation called co-morbidity. Here are a few of the disorders commonly associated with concussions:

  • One in five people who have a concussion later suffer from anxiety.
  • About 18% of people suffer from depression post-concussion.
  • Sleep disorders are more common in people who have had a concussion.
  • Concussions increase the risk of brain-related medical disorders such as stroke and epilepsy.

Concussion Brain Science

Scientists are trying to understand the biochemical changes occurring in the brain as a result of a concussion. A more thorough understanding of the process will make it easier to find treatments that can aid in recovery from concussions and decrease the risk of long-term damage from future injuries.

Areas of current research include:

  • Risk of future neurological decline. Some studies have found that even a single concussion can lead to an increased risk of developing dementia or Parkinson’s disease later in life. The link between concussions and these degenerative conditions is not clear; some theories suggest the cause could be concussion-related inflammation, abnormal protein buildup, or merely an increase in the brain’s general vulnerability after a concussion. Research is ongoing.
  • Search for cures. While researchers seek to understand better exactly what happens in the brain after a concussion, other scientists are looking for new therapies that can bolster the brain’s ability to recover from the injury. Researchers in Canada have conducted non-invasive therapy studies using low-frequency magnetic fields on rodents that have suffered a concussion. The study results suggest that the therapy can help to speed recovery and may even protect the brain from further degeneration in the future. Human trials of the treatment are planned in the future.

Concussion Research

Title: Aerobic Exercise for Concussion

Stage: Recruiting 

Principal Investigators: John Leddy, MD, Christina Master, MD, Rebekah Mannix, MD   

Children’s Hospital of Philadelphia

Philadelphia, PA

The use of aerobic exercise treatment in the chronic phase of concussion recovery is well-described in the literature. Still, there are limited existing data on the effect of exercise treatment in the acute phase after sport-related concussion (SRC). This study will compare adolescents’ outcomes with a recent SRC who are randomized to sub-threshold aerobic exercise versus those randomized to placebo stretching to evaluate the effect of aerobic exercise in the acute recovery phase.


Title: The Effects of Head Trauma on Collegiate Athletes

Stage: Recruiting 

Principal Investigator: William P Meehan III, MD

Boston Children’s Hospital

Boston, MA

Recently, researchers and clinicians have examined many different forms of concussion testing to assess if a brain injury has occurred and to what degree it affects the individual being tested. Due to the multi-faceted and complex presentation of concussive injuries and the unknown effects of repeated head trauma, it is unlikely that a single test of physiological or behavioral function will reflect the full range of injury-related damages from a concussive event or from a series of cumulative head traumas, as well as the injury response within brain tissue. However, by combining various objective assessments that may detect structural and functional alterations following head trauma into a single study, a clearer understanding of the multi-faceted presentation resulting from head trauma may be identified. The identification of biomarkers and the utilization of objective and clinically feasible tools will provide a method to assess three domains across multiple systems affected by head trauma: 1) the prognostic value of initial concussion assessments to identify injury severity and factors responsible for prolonged recovery, 2) the temporal window of recovery and potential vulnerability of brain tissue post-injury, and 3) the long-term alterations associated with repeated head trauma exposure.


Title: Development of a Neurocognitive Screening Test

Stage: Recruiting 

Contact: Jane Luce, MPH

ImPACT Applications, Inc.

San Diego, CA

This research study will evaluate a standalone software application designed to standardize and validate new neurocognitive screening testing for children aged 6 through 11 and adolescents and adults ages 12 through 75.

 The purpose of this study is to evaluate recently developed computerized tasks sensitive to changes in neurocognitive performance after a concussion. These tests were designed to measure the effects of concussion on cognitive processes (e.g., memory, attention, brain speed) and visual functioning. 

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