In the largest study of its kind, researchers have found that having three or more concussions is linked with worsened brain function in later life, and that just one moderate-to-severe concussion, or traumatic brain injury (TBI), could have a long-term impact on brain function, including memory.
Although it is clear that TBI causes cognitive deficits, the time course of these deficits, the cognitive domains most affected, and the impact of repeat TBI remain subjects of debate.
Led by teams at the University of Oxford and the University of Exeter, with collaboration from the University of New South Wales Australia, Kings College London and University College London, Stavanger University Hospital in Norway and Harvard Medical School in the US, the research included data from more than 15 000 UK-based participants of the online PROTECT study, aged between 50 and 90. They reported the severity and frequency of concussions they had experienced throughout their lives, and completed annual, computerised tests for brain function.
Published in the Journal of Neurotrauma, the paper found that people who reported three or more concussions had significantly worse cognitive function, which got successively worse with each subsequent concussion after that. Attention and completion of complex tasks were particularly affected.
Researchers say people who have had concussions should be warned of the dangers of continuing high-risk sport or work.
Lead investigator Dr Vanessa Raymont, from the University of Oxford, said: “We know that head injuries are a major risk factor for dementia, and this large-scale study gives the greatest detail to date on a stark finding – the more you injure your brain in life, the worse your brain function could be as you age.
“Our research indicates that people who’ve had three or more even mild episodes of concussion should be counselled on whether to continue high-risk activities. We should also encourage organisations operating in areas where head impact is more likely to consider how they can protect their athletes or employees."
The study showed that those who had reported three episodes of even mild concussion throughout their lives had significantly worse attention and ability to complete complex tasks. Those with four or more mild concussion episodes also showed worsened processing speed and working memory. Each additional reported concussion was linked to progressively worse cognitive function.
Furthermore, the researchers found that reporting even one moderate-to-severe concussion was associated with worsened attention, completion of complex tasks and processing speed capacity.
In the online PROTECT study, participants share detailed lifestyle information, and complete a suite of cognitive tests every year, for up to 25 years. This rich mine of data helps researchers understand how the brain ages, and the factors involved in maintaining a healthier brain in later life.
Dr Helen Brooker, a study co-author from the University of Exeter, said: “As our population ages, we urgently need new ways to empower people to live healthier lives later on. This paper highlights the importance of detailed long-term studies like PROTECT in better understanding head injuries and the impact to long term cognitive function, particularly as concussion has also been linked to dementia.
“Life events that might seem insignificant, like a mild concussion, can have an impact on the brain. Our findings indicate that cognitive rehabilitation should focus on key functions, like attention and completion of complex tasks, which we found were susceptible to long-term damage."
Dr Susan Kohlhaas, director of research at Alzheimer’s Research UK, said: “Studies like this are so important in unravelling the long-term risks of traumatic brain injury, including their effect on dementia risk. These findings should send a clear message to policy makers and sporting bodies, who should put robust guidelines in place that reduce risk of head injury as much as possible."
Study details
Lifetime Traumatic Brain Injury and Cognitive Domain Deficits in Late Life: The PROTECT-TBI Cohort Study
Matthew Lennon, Helen Brooker, Byron Creese, Tony Thayanandan, Grant Rigney, Dag Aarsland, Adam Hampshire, Clive Ballard, Anne Corbett, Vanessa Raymont.
Published in the Journal of Neurotrauma on 27 January 2023
Abstract
Traumatic brain injury (TBI) causes cognitive impairment but it remains contested regarding which cognitive domains are most affected. Further, moderate-severe TBI is known to be deleterious, but studies of mild TBI (mTBI) show a greater mix of negative and positive findings. This study examines the longer-term cognitive effects of TBI severity and number of mTBIs in later life. We examined a subset (n = 15,764) of the PROTECT study, a cohort assessing risk factors for cognitive decline (ages between 50 and 90 years). Participants completed cognitive assessments annually for 4 years. Cognitive tests were grouped using a principal components analysis (PCA) into working memory, episodic memory, attention, processing speed, and executive function. Lifetime TBI severity and number were retrospectively recalled by participants using the Brain Injury Screening Questionnaire (BISQ). Linear mixed models (LMMs) examined the effect of severity of head injury (non-TBI head strike, mTBI, and moderate-severe TBI) and number of mTBI at baseline and over time. mTBI was considered as a continuous and categorical variable (groups: 0 mTBI, 1 mTBI, 2 mTBIs, 3 mTBIs, and 4+ mTBIs).
Of the participants 5725 (36.3%) reported at least one mTBI and 510 (3.2%) at least one moderate-severe TBI, whereas 3711 (23.5%) had suffered at worst a non-TBI head strike and 5818 (32.9%) reported no head injuries. The participants had suffered their last reported head injury an average (standard deviation, SD) of 29.6 (20.0) years prior to the study. Regarding outcomes, there was no worsening in longitudinal cognitive trajectories over the study duration but at baseline there were significant cognitive deficits associated with TBI.
At baseline, compared with those without head injury, individuals reporting at least one moderate-severe TBI had significantly poorer attention (B = −0.163, p< 0.001), executive scores (B = −0.151, p = 0.004), and processing speed (B = −0.075, p = 0.033). Those who had suffered at least a single mTBI also demonstrated significantly poorer attention scores at baseline compared with the no head injury group (B = −0.052, p = 0.001). Compared with those with no mTBI, those in the 3 mTBI group manifested poorer baseline executive function (B = −0.149, p = 0.025) and attention scores (B = −0.085, p = 0.015). At baseline, those who had suffered four or more mTBIs demonstrated poorer attention (B = −0.135, p < 0.001), processing speed (B = −0.072, p = 0.009), and working memory (B = −0.052, p = 0.036), compared with those reporting no mTBI. TBI is associated with fixed, dose, and severity-dependent cognitive deficits.
The most sensitive cognitive domains are attention and executive function, with approximately double the effect compared with processing speed and working memory. Post-TBI cognitive rehabilitation should be targeted appropriately to domain-specific effects. Significant long-term cognitive deficits were associated with three or more lifetime mTBIs, a critical consideration when counselling individuals post-TBI about continuing high-risk activities.
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