A Primer on Traumatic Brain Injury and Concussions

In recent years, the psychosocial consequences of traumatic brain injury (TBI) have gained increased media attention and has emerged  as a significant public health challenge. TBI and concussion, a subtype of mild TBI, are “defined as a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces.”1 Concussion may be due to a direct blow to the head, face, neck, or from ‘impulsive’ force transmitted to the head from trauma inflicted on other parts of the body. It may occur with or without loss of consciousness.   

A concussion may produce a rapid onset of neurologic impairments which resolve quickly or symptoms may emerge and resolve over a longer period of time. They can produce structural brain abnormalities which may not be detectable on standard neuroimaging studies. 

Every year, over 1.5 million people in the U.S. suffer a TBI2 with most cases being mild TBIs.3,4 The most common causes of TBI are motor vehicle accidents, falls (especially common among the elderly), occupational and recreational accidents and assaults.5,6 Mild TBIs are common in high contact sports such as American football, ice hockey, soccer, and boxing.7 Soldiers exposed to combat related environments may experience TBI due to blasts or explosions, falls, motor vehicle accidents, shrapnel, or bullet wounds.8 Other risk factors for TBI are male gender, ages between 15 and 34, lower socioeconomic status, lower levels of cognitive functioning, and a history of serious substance use disorders.4,5

Proposed mechanisms for the neurological deficits associated with mild TBIs include axonal damage from shearing forces, disruption of axonal neurofilament organization, axonal swelling Wallerian degeneration, and transection.10 Studies suggest that neurophysiological changes associated with mild TBI may be secondary to the release of excitatory neurotransmitters (e.g.acetylcholine, glutamate, and aspartate) and the production of free radicals.11

Clinical Features

Confusion and amnesia are the primary symptoms of concussion and can occur with or without loss of consciousness.12,13 The frequency of sports related concussions without loss of consciousness may contribute to underdiagnosis of TBIs among athletes.14