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.
If repeated vomiting, worsening headache, dizziness, seizure activity, excessive drowsiness, double vision, slurred speech, unsteady walk, or weakness or numbness in arms or legs, or signs of basilar skull fracture develop, immediate assessment in an emergency department is needed. Observation to monitor for worsening condition is an important part of treatment. People may be released after assessment from their primary care medical clinic, hospital, or emergency room to the care of a trusted person with instructions to return if they display worsening symptoms or those that might indicate an emergent condition ("red flag symptoms") such as change in consciousness, convulsions, severe headache, extremity weakness, vomiting, new bleeding or deafness in either or both ears. Education about symptoms, their management, and their normal time course, may lead to an improved outcome. Rest and return to physical and cognitive activity
Physical and cognitive rest is recommended for the first 24–48 hours following a concussion after which injured persons should gradually start gentle low-risk physical and cognitive activities that do not make current symptoms worse or bring on new symptoms. Any activity for which there is a risk of contact, falling, or bumping the head should be avoided. Low-risk activities can be started even while a person has symptoms, as long as the activity does not worsen existing symptoms or bring on new concussion symptoms. Resting for longer than 24–48 hours follow concussion has been shown to be associated with longer recovery.