concussion concussion a concussion, also known as a mild traumatic brain injury (mtbi), is a head injury that temporarily affects brain functioning. symptoms may include loss of consciousness (loc); memory loss; headaches; difficulty with thinking, concentration, or balance; nausea; blurred vision; sleep disturbances, and mood changes. any of these symptoms may begin immediately, or appear days after the injury. concussion should be suspected if a person indirectly or directly hits their head and experiences any of the symptoms of concussion. symptoms of a concussion may be delayed by 1-2 days after the accident. it is not unusual for symptoms to last 2 weeks in adults and 4 weeks in children. fewer than 10% of sports-related concussions among children are associated with loss of consciousness. for concussion (mild traumatic brain injury) in children and adolescents, see pediatric concussion. concussionother namesmild brain injury, mild traumatic brain injury (mtbi), mild head injury (mhi), minor head traumaacceleration (g-forces) can exert rotational forces in the brain, especially the midbrain and diencephalon.specialtyemergency medicine, neurologysymptomsheadache; trouble with thinking, memory, or concentration; nausea; blurry vision; sleep disturbances; mood changescomplicationschronic traumatic encephalopathy, parkinson's disease, depression, post-concussion syndromedurationup to 4 weekscausesmotor vehicle collisions, falls, sports injuries, bicycle accidentsrisk factorslack of earthquake preparedness, physical violences, drinking alcohol, playing contact sports such as american football, playing martial arts such as muay thai, previous history of concussiondiagnostic methodbased on symptomspreventionearthquake preparedness, head protection equipment, like hard hats, gridiron football, martial arts, motorcycle, or bicycle helmets treatmentphysical and cognitive rest for a day or two with a gradual return to activitiesmedicationparacetamol (acetaminophen), nsaidsfrequency6 per 1,000 people a year common causes include motor vehicle collisions, falls, sports injuries, and bicycle accidents. risk factors include lack of earthquake preparedness, physical violence, drinking alcohol and a prior history of concussion. the mechanism of injury involves either a direct blow to the head or forces elsewhere on the body that are transmitted to the head. this is believed to result in neuron dysfunction, as there are increased glucose requirements, but not enough blood supply. a thorough evaluation by a qualified medical provider (such as a physician, physician assistant, or nurse practitioner) is required to rule out life-threatening head injuries, injuries to the cervical spine, and neurological conditions. glasgow coma scale score 13 to 15, loss of consciousness for less than 30 minutes, and memory loss for less than 24 hours may be used to rule out moderate or severe traumatic brain injuries. diagnostic imaging such as a ct scan or an mri may be required to rule out severe head injuries. routine imaging is not required to diagnose concussion. prevention of concussions includes the use of a helmet when bicycling or motorbiking. treatment includes physical and mental rest for 1–2 days, with a gradual step-wise return to activities, school, and work. prolonged periods of rest may slow recovery and result in greater depression and anxiety. paracetamol (acetaminophen) or nsaids may be recommended to help with a headache. prescribed aerobic exercise may improve recovery. physiotherapy may be useful for persistent balance problems, headache, or whiplash; cognitive behavioral therapy may be useful for mood changes. evidence to support the use of hyperbaric oxygen therapy and chiropractic therapy is lacking. worldwide, concussions are estimated to affect more than 3.5 per 1,000 people a year. concussions are classified as mild traumatic brain injuries and are the most common type of tbis. males and young adults are most commonly affected. outcomes are generally good. another concussion before the symptoms of a prior concussion have resolved is associated with worse outcomes. repeated concussions may also increase the risk in later life of chronic traumatic encephalopathy, parkinson's disease and depression. signs and symptoms concussion symptoms vary between people and include physical, cognitive, and emotional symptoms. symptoms may appear immediately or be delayed y 1-2 days. delayed onset of symptoms may still be serious and require a medical assessment. up to one-third of people with concussion experience prolonged or persistent concussion symptoms, also known as post concussion syndrome, which is defined as concussion symptoms lasting for 4 weeks or longer in children and adolescents, and symptoms lasting for more than 14 days in an adult. the severity of the initial symptoms is the strongest predictor of recovery time in adults. physical headaches are the most common mtbi symptom. others include dizziness, vomiting, nausea, lack of motor coordination, difficulty balancing, or other problems with movement or sensation. visual symptoms include light sensitivity, seeing bright lights, blurred vision, and double vision. tinnitus, or a ringing in the ears, is also commonly reported. in one in about seventy concussions, concussive convulsions occur, but seizures that take place during or immediately after a concussion are not "post-traumatic seizures", and, unlike post-traumatic seizures, are not predictive of post-traumatic epilepsy, which requires some form of structural brain damage, not just a momentary disruption in normal brain functioning. concussive convulsions are thought to result from temporary loss or inhibition of motor function and are not associated either with epilepsy or with more serious structural damage. they are not associated with any particular sequelae and have the same high rate of favorable outcomes as concussions without convulsions. cognitive and emotional cognitive symptoms include confusion, disorientation, and difficulty focusing attention. loss of consciousness may occur, but is not necessarily correlated with the severity of the concussion if it is brief. post-traumatic amnesia, in which events following the injury cannot be recalled, is a hallmark of concussions. confusion may be present immediately or may develop over several minutes. a person may repeat the same questions, be slow to respond to questions or directions, have a vacant stare, or have slurred or incoherent speech. other concussion symptoms include changes in sleeping patterns and difficulty with reasoning, concentrating, and performing everyday activities. a concussion can result in changes in mood including crankiness, loss of interest in favorite activities or items, tearfulness, and displays of emotion that are inappropriate to the situation. common symptoms in concussed children include restlessness, lethargy, and irritability. mechanism rotational force is key in a concussion. punches in boxing can deliver more rotational force to the head than the typical impact in american football. forces the brain is surrounded by cerebrospinal fluid, which protects it from light trauma. more severe impacts, or the forces associated with rapid acceleration, may not be absorbed by this cushion. concussions, and other head-related injuries, occur when external forces acting on the head are transferred to the brain. such forces can occur when the head is struck by an object or surface (a 'direct impact'), or when the torso rapidly changes position (i.e. from a body check) and force is transmitted to the head (an 'indirect impact'). forces may cause linear, rotational, or angular movement of the brain or a combination of them. in rotational movement, the head turns around its center of gravity, and in angular movement, it turns on an axis, not through its center of gravity. the amount of rotational force is thought to be the major component in concussion and its severity. as of 2007, studies with athletes have shown that the amount of force and the location of the impact are not necessarily correlated with the severity of the concussion or its symptoms, and have called into question the threshold for concussion previously thought to exist at around 70–75 g. the parts of the brain most affected by rotational forces are the midbrain and diencephalon. it is thought that the forces from the injury disrupt the normal cellular activities in the reticular activating system located in these areas and that this disruption produces the loss of consciousness often seen in concussion. other areas of the brain that may be affected include the upper part of the brain stem, the fornix, the corpus callosum, the temporal lobe, and the frontal lobe. angular accelerations of 4600, 5900, or 7900 rad/s2 are estimated to have 25, 50, or 80% risk of mtbi respectively. pathophysiology in both animals and humans, mtbi can alter the brain's physiology for hours to years, setting into motion a variety of pathological events. as one example, in animal models, after an initial increase in glucose metabolism, there is a subsequent reduced metabolic state which may persist for up to four weeks after injury. though these events are thought to interfere with neuronal and brain function, the metabolic processes that follow concussion are reversible in a large majority of affected brain cells; however, a few cells may die after the injury. included in the cascade of events unleashed in the brain by concussion is impaired neurotransmission, loss of regulation of ions, deregulation of energy use and cellular metabolism, and a reduction in cerebral blood flow. excitatory neurotransmitters, chemicals such as glutamate that serve to stimulate nerve cells, are released in excessive amounts. the resulting cellular excitation causes neurons to fire excessively. this creates an imbalance of ions such as potassium and calcium across the cell membranes of neurons (a process like excitotoxicity). at the same time, cerebral blood flow is relatively reduced for unknown reasons, though the reduction in blood flow is not as severe as it is in ischemia. thus cells get less glucose than they normally do, which causes an "energy crisis". concurrently with these processes, the activity of mitochondria may be reduced, which causes cells to rely on anaerobic metabolism to produce energy, increasing levels of the byproduct lactate. for a period of minutes to days after a concussion, the brain is especially vulnerable to changes in intracranial pressure, blood flow, and anoxia. according to studies performed on animals (which are not always applicable to humans), large numbers of neurons can die during this period in response to slight, normally innocuous changes in blood flow. concussion involves diffuse (as opposed to focal) brain injury, meaning that the dysfunction occurs over a widespread area of the brain rather than in a particular spot. it is thought to be a milder type of diffuse axonal injury, because axons may be injured to a minor extent due to stretching. animal studies in which rodents were concussed have revealed lifelong neuropathological consequences such as ongoing axonal degeneration and neuroinflammation in subcortical white matter tracts. axonal damage has been found in the brains of concussion patients who died from other causes, but inadequate blood flow to the brain due to other injuries may have contributed. findings from a study of the brains of deceased nfl athletes who received concussions suggest that lasting damage is done by such injuries. this damage, the severity of which increases with the cumulative number of concussions sustained, can lead to a variety of other health issues. the debate over whether concussion is a functional or structural phenomenon is ongoing. structural damage has been found in the mildly traumatically injured brains of animals, but it is not clear whether these findings would apply to humans. such changes in brain structure could be responsible for certain symptoms such as visual disturbances, but other sets of symptoms, especially those of a psychological nature, are more likely to be caused by reversible pathophysiological changes in cellular function that occur after concussion, such as alterations in neurons' biochemistry. these reversible changes could also explain why dysfunction is frequently temporary. a task force of head injury experts called the concussion in sport group met in 2001 and decided that "concussion may result in neuropathological changes but the acute clinical symptoms largely reflect a functional disturbance rather than structural injury." using animal studies, the pathology of a concussion seems to start with mechanical shearing and stretching forces disrupting the cell membrane of nerve cells through "mechanoporation". this results in potassium outflow from within the cell into the extracellular space with the subsequent release of excitatory neurotransmitters including glutamate which leads to enhanced potassium extrusion, in turn resulting in sustained depolarization, impaired nerve activity and potential nerve damage. human studies have failed to identify changes in glutamate concentration immediately post-mtbi, though disruptions have been seen 3 days to 2 weeks post-injury. in an effort to restore ion balance, the sodium-potassium ion pumps increase activity, which results in excessive atp (adenosine triphosphate) consumption and glucose utilization, quickly depleting glucose stores within the cells. simultaneously, inefficient oxidative metabolism leads to anaerobic metabolism of glucose and increased lactate accumulation. there is a resultant local acidosis in the brain and increased cell