mild traumatic brain injury

How side hit to the head could damage brain, lead to concussion

While probing the origins of concussion, researchers identify which regions of the brain are more vulnerable to damage

August 1, 2019

Science Daily/Stevens Institute of Technology

Play contact sports for any length of time and at one point or another you're probably going to have your 'bell rung' by a powerful blow to the head from a hard hit or fall. Rising awareness of the severe, abiding repercussions of strong impacts to the head -- concussions, mild traumatic brain injury, neurological disorders -- have led scientists to focus on what exactly happens inside a skull during a big hit.


Mehmet Kurt, a mechanical engineer at Stevens Institute of Technology who studies the biomechanics of the brain and the skull at rest and during rapid head movements, has now bioengineered simulations that track how the brain behaves upon impact, reconstructing the inertial stresses and strains that prevail inside a brain that's just been hit hard from the side.


"The brain not only rings, but it has a distinct pattern of ringing when the head is hit from the side and experiences rotational acceleration," said Kurt, whose work may not only have implications for brain injury assessment, but for sports helmet makers in search of measurable parameters that can simply distinguish 'concussion' from 'no concussion' to help the industry set safety standards. The paper appears in the July 30 issue of Physical Review Applied.


By analyzing a combination of simulated and human data of brain movement that have led to concussions, Kurt and his group, including Stevens graduate student Javid Abderezaei, digitally reveal that side impacts to the head lead to rotational accelerations that cause mechanical vibrations to concentrate in two brain regions: the corpus collosum, the bridge that links the hemispheres, and the periventricular region, white matter lobes at the brain's root that help speed muscle activation.


Kurt and Abderezaei, with Kaveh Laksari of University of Arizona and Songbai Ji of Worcester Polytechnic Institute, found that the skull's internal geometry and the gelatinous nature of the brain cause these two regions to resonate at certain frequencies and receive more mechanical energy in the form of shearing forces than the rest of the brain. More shear strain presumably yields more tissue and cell damage, particularly since shear, opposing motions tend to deform brain tissue more readily than other biological tissues.


"A hit to the head creates non-linear movement in the brain," said Abderezaei. "That means that small increases in amplitude can lead to unexpectedly big deformations in certain structures."


These non-linear vibrations are not surprising in a complex organ featuring a range of tissue densities. Add in the restraining effects of the tough protective membranes, particularly the falx and the tentorium, that hold the brain in place from both above and below, and certain regions are bound to come off worse in side hits.


Identifying the parts of the brain that are most at hazard in side impacts makes them prime targets for further investigation in quest of insights into concussions and detailed brain behavior in collisions. Such knowledge can't come soon enough more than 300,000 American children and teenagers suffer sports-related concussions every year.

Brain area tied to emotions is larger in vets, service members with mild TBI and PTSD

'An intriguing structural finding'

April 29, 2019

Science Daily/Veterans Affairs Research Communications

A new study finds that veterans and active-duty service members with combat-related PTSD and mild traumatic brain injury had larger amygdalas -- the region of the brain that processes such emotions as fear, anxiety, and aggression -- than those with only brain injuries.


The findings appeared online April 25 in the Journal of Head Trauma Rehabilitation.


Through magnetic resonance imaging, the researchers found that the right and left sides of the amygdala in people with combat-related PTSD and mild traumatic brain injury (mTBI) were larger than those in people with only combat-related mTBI. The amygdala is an almond-shaped section of tissue in the temporal portion of the brain and is key to triggering PTSD symptoms.


The researchers caution that the findings were based on an observational study and therefore can't prove a cause-and-effect relationship -- only a correlation.


The study included 89 veterans and active-duty military personnel, about a third of whom had both PTSD and mTBI. The rest formed the mild-TBI-only control group. A mild traumatic brain injury is also known as a concussion.


"This is an intriguing structural finding, given the role of the amygdala in the challenging [neuropsychological] symptoms witnessed in casualties of combat-related mTBI and PTSD," the researchers write. "Further investigation is needed to determine whether amygdala size could be used to screen people at risk for PTSD, or whether it could be used to monitor the [effectiveness of medical solutions]."


The study's lead author, Dr. Mingxiong Huang, is a neuroimaging scientist at the VA San Diego Health Care System. He says the finding of a larger amygdala in veterans with combat-related PTSD and mTBI was a bit of a surprise.


"Some previous PTSD research showed declines in amygdala volume based on the assumption of a loss of size due to injuries," says Huang, also a professor in the department of radiology at the University of California San Diego (UCSD). "Our finding of increased amygdala volume seems to point to different mechanisms, such as an exposure to repetitive fear and stress."


Such exposure, he adds, may lead to an abnormal growth of the neural networks within the amygdala, a development that has been reported in animal studies but hasn't been fully explored in human PTSD studies. More studies involving people with non-combat PTSD are needed to generalize this finding to other types of PTSD, he notes.


A co-author of the paper, Dr. Douglas Chang, is a physician and researcher at VA San Diego.


"The amygdala is involved with processing threat perception and arousal and with linking emotion to experience in complex ways," says Chang, who is also a professor of orthopedic surgery at UCSD. "A larger amygdala volume may be a sign of hyperactivity with an enlarged neural network. But we don't know whether this is an attempt by the brain to cope with PTSD or whether the growth and enlargement is causing symptoms, like an electrical storm."


He adds: "The situation may also resemble scar tissue formation on skin. Is this an organized response by the body to heal itself, or is the scar tissue going haywire and forming a grossly disfigured area? Another possibility is that this study simply identified at-risk people for PTSD with a pre-existing condition: an enlarged amygdala."


Combat-related PTSD and mTBI are leading health care concerns in veterans and service members. It's not unusual for both conditions to occur in the same person, based on evidence from a cross section of studies. Some of the symptoms are similar, such as depression, anxiety, insomnia, fatigue, and changes in memory and concentration. However, the effects of PTSD and mTBI on neural pathways in the brain, as well as the impact of the co-existence of the two, are not fully understood.


Scientists in Huang's study conducted the testing at VA San Diego and at two Marine Corps bases in California. They measured intracranial volume, a key statistic used to analyze the size of the brain and brain regions, especially in cases of neurodegenerative diseases.


The size of the right amygdala was 0.122 percent of total brain volume, on average, in the group with mTBI and PTSD. It was 0.115 percent in the cohort with only mTBI. The size of the left amygdala was 0.118 percent of brain volume in those with mTBI and PTSD, compared with 0.112 percent in the mTBI group. The researchers found both of those differences to be "statistically significant."


The study team also examined the caudate, the hippocampus, the anterior cingulate cortex, and the cerebral cortex. Those brain regions, like the amygdala, are in the limbic system, which controls basic emotions, including fear, pleasure, and anger. The researchers found no "statistically significant" differences in those regions, suggesting that only changes in the amygdala are linked to PTSD symptoms in people with mTBI, according to Chang.


The study authors say the findings have several implications for research and treatment.


"To be able to see a structural difference between these two cohorts and in this stage of PTSD really points to something going on with the amygdala," Chang says. "Can we use this as a screening tool to identify people at risk? Maybe this is an adaptive response that we can monitor and use to track different kinds of mental health treatment approaches. Maybe yoga is helpful, maybe mindfulness meditation is helpful, maybe exercise is helpful. Perhaps there are drugs that can protect somebody against these traumas or to help improve their conditions. To be able to identify something that's changed in a quantitative way is amazing. It opens the door to many possibilities to help treat this problem."

New insights into the circuitry of PTSD, mild traumatic brain injury

July 23, 2015

Science Daily/Elsevier

Posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) can have devastating consequences. Both are associated with high rates of disability and suicide, and although they are separate conditions, they commonly co-occur. For example, a soldier who has developed PTSD as a result of a traumatic experience may have also sustained a brain injury during that experience.


Significant research has been conducted to understand the brain mechanisms underlying PTSD and TBI, but there has still been a lack of knowledge regarding exactly which brain networks are disturbed in these disorders.


To fill this gap, Dr. Jeffrey Spielberg and his colleagues at the VA Boston Healthcare System examined brain networks in veterans with trauma exposure using functional magnetic resonance imaging and graph theory tools. As the authors explain, graph theory is a sophisticated analysis that allows us to understand brain networks at a level of complexity that was previously impossible. It permits examination of the patterns of brain connections, as opposed to examining individual connections.


The researchers recruited 208 veterans of Operation Enduring Freedom, Operation Iraqi Freedom, and Operation New Dawn, all of whom had experienced a traumatic event. They found that veterans who had more severe PTSD re-experiencing symptoms (e.g., flashbacks or reliving the event) showed weaker connectivity in two networks.


The first altered network includes the hippocampus and prefrontal cortex, and is involved in providing contextual information. This suggests that perhaps the hippocampus may be overgeneralizing trauma-related memories, and therefore, fails to correctly classify non-threatening cues as "safe."


The second network, which was identified only in veterans with comorbid mild TBI, includes the basal ganglia and prefrontal cortex, and plays a role in working memory.


Because the veterans studied here had already experienced a traumatic event, this research cannot identify with certainty whether the observed brain network disturbances were present in these individuals before the trauma occurred, or whether they occurred as a result of the trauma exposure. Future research of at-risk individuals, perhaps examining soldiers before and after military deployment, will be necessary to clarify this point.


"It may never be possible to fully distinguish the role of the severity of stress, the capacity for resilience to stress effects, and the presence of mild TBI in PTSD-related distress and disability because these factors are so complex and intimately entwined," said Dr. John Krystal, Editor of Biological Psychiatry.


"However, this study suggests that there are subtle but important differences in brain circuit functional connectivity related to the impact of traumatic stress among individuals with and without TBI. These data provide additional evidence that TBI may complicate the capacity for recovery from traumatic stress-related symptoms."

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