Traumatic brain injury (TBI) is a leading cause of death and disability in young adults [1]. In addition to impairments stemming from the initial trauma, these types of injuries can alter the brain in ways that may not become apparent until years later [2]. These changes can impact cognitive function and make the brain more vulnerable to neurodegenerative disease.
TBI occurs when a strong external force acts on the head, causing the brain to move around in the skull, or when an object penetrates the skull into the brain [3]. The rapid movement of the brain can lead to tearing, and bruising occurs in places where the brain slams into the skull.
Motor vehicle-related crashes are the most common cause of TBI in adolescents and young adults, while older adults are more likely to experience a TBI due to a fall [3]. Sports, intimate partner violence, and assaults are other common triggers of brain injury.
TBIs can range in severity. The most common type of mild TBI is a concussion [4]. Mild TBIs are vastly underdiagnosed and misdiagnosed because they typically do not induce obvious structural changes to the brain based on brain imaging. More importantly, many people are unaware that they have even incurred a mild brain injury, because they do not experience symptoms immediately following the bump to the head. As a result, they are unlikely to seek medical attention.
However, physical symptoms often do not occur until hours or days later [3]. These may include headaches, dizziness, fatigue, and confusion. Additionally, cognitive symptoms and mood changes may take months or even years to emerge, at which point, people are less likely to realize they are linked to a prior head injury.
It is important to seek appropriate medical attention, and not ignore these symptoms, because initial TBI severity is a poor predictor of long-term disability [5].
The brain is plastic and will undergo changes in response to injury [6]. Some of these changes may negatively affect the ability of the brain to carry out certain functions. These could lead to difficulties with thinking, movement, or emotional regulation, and will vary from person to person depending on their age, the type of injury, and the way their brain adapted. The full impact may not be felt until years or decades later. Because these effects may not be apparent right away, TBI-related disability has been referred to as a silent or hidden epidemic.
One of these long-term effects is an increased risk for dementia [2; 7]. Several studies have found that there is a dose-response relationship, such that more severe and more frequent TBIs are associated with higher risk [2; 8]. The association with moderate to severe TBI is strong enough to be listed as a modifiable risk factor by the Lancet Commission on dementia [9]. The risk related to mild TBI has been less clear, which may be because there is a lot more variability in the type of brain remodeling and occurrence of long-term disability in mild cases [8]. Patient-specific factors, such as age, lifestyle, and comorbidities, may influence whether the brain adapts to the mild injury in a restorative or deleterious manner [5].
Some of the remodeling mechanisms may trigger the formation of brain pathology, such as the buildup of toxic proteins [8]. The damage from the injury may also make the brain less resilient to this pathology.
Cognitive decline emerging within a year of TBI, particularly in older adults, can indicate that the person was already in early stages of dementia when the injury occurred, since dementia increases the risk of TBI from falls and other types of accidents [2; 7].
Practicing safe driving habits and engaging in strength and balance training can help reduce the risk of car accidents and falls, respectively. While it isn’t possible to fully prevent the types of incidents that lead to TBI, measures can be taken to mitigate the chance of sustaining a brain injury, when they do occur. Wearing seatbelts in motor vehicles and helmets while engaging in sports can protect against severe brain injury [10; 11].
Remember, that feeling fine right after an accident does not necessarily mean that an injury has not occurred. Document any incidents that impact the head, with the awareness that effects may take a long time to emerge. Seek medical attention at the first sign of symptoms, and have regular follow-ups to monitor for delayed effects.
Betsy Mills, PhD, is a member of the ADDF's Aging and Alzheimer's Prevention program. She critically evaluates the scientific evidence regarding prospective therapies to promote brain health and/or prevent Alzheimer's disease, and contributes to CognitiveVitality.org. Dr. Mills came to the ADDF from the University of Michigan, where she served as the grant writing manager for a clinical laboratory specializing in neuroautoimmune diseases. She also completed a Postdoctoral fellowship at the University of Michigan, where she worked to uncover genes that could promote retina regeneration. She earned her doctorate in neuroscience at Johns Hopkins University School of Medicine, where she studied the role of glial cells in the optic nerve, and their contribution to neurodegeneration in glaucoma. She obtained her bachelor's degree in biology from the College of the Holy Cross. Dr. Mills has a strong passion for community outreach, and has served as program presenter with the Michigan Great Lakes Chapter of the Alzheimer's Association to promote dementia awareness.
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