Sports-Related Concussions in Youth Improving the Science, Changing the Culture (2014) / Chapter Skim
Currently Skimming:
2 Neuroscience, Biomechanics, and Risks of Concussion in the Developing Brain
2 Neuroscience, Biomechanics, and Risks of Concussion in the Developing Brain
Pages 55-98
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 55... ...
This area of research originally focused on adult animal models of moderate to severe brain injuries, and these models have significantly contributed to our understanding of the biomechanics and neurochemical changes that occur after TBI. More recently, research efforts have focused on animal models of mild TBI (mTBI)
|
From page 56... ...
The techniques do, however, allow for assessment of functional sequelae of concussions and, together with animal models, suggest that the developing brain responds differently to concussion than does the mature brain (Choe et al., 2012; Shrey et al., 2011)
|
From page 57... ...
Longitudinal studies using magnetic resonance imaging (MRI) to map the developmental time-course of structural changes in the normal brain indicate that increases in white matter are linear throughout childhood and adolescence and continue well into young adulthood.
|
From page 58... ...
. Several studies have demonstrated that females from 4 to 8 years of age and between 10 and 16 years of age show greater middle cerebral artery and basilar artery blood flow velocities relative to males of the same age (Tontisirin et al., 2007; Vavilala et al., 2005)
|
From page 59... ...
or functional (changes in blood flow or neurological status) , and they may be immediate or delayed.
|
From page 60... ...
Overview of Common Experimental Platforms for Understanding the Biomechanics of Traumatic Brain Injury Investigators can use human data obtained in the field during sporting events to help understand what scenarios cause concussion. Typically, a sensor affixed to a helmet or a mouthpiece is used to measure the magnitude,
|
From page 61... ...
In 2012 the U.S. Army began using sensors to collect data on the effects of blasts on the body, including the mechanisms that lead to concussions and other traumatic brain injury in soldiers.
|
From page 62... ...
As is the case with surrogates, computational models cannot be used to directly measure concussion or axonal injury, skull fracture, or vessel rupture; instead, predicted deformations or stresses from the model must be compared to published tissue-specific thresholds in order to infer injury. An important point is that early data have demonstrated that the brain tissue distortions and stresses in the skull that are associated, respectively, with axonal injury and skull fracture are smaller in young children than in adults (Coats and Margulies, 2006; Ibrahim et al., 2010; Raghupathi and Margulies, 2002; Robbins and Wood, 1969)
|
From page 63... ...
Animal models are useful for measuring physiological responses (e.g., reflexes, blood flow, tissue oxygen content, metabolic derangements) ; injuries to the vessels, axons, and neural cell bodies; and changes in motor, memory, learning, and behavioral aptitudes at prescribed time-points after injury.
|
From page 64... ...
What Has Been Learned About How Traumatic Brain Injuries Occur Using the tools described above, researchers have determined that with or without a helmet, when the head contacts a stationary or moving object there is a rapid change in velocity and a possible deformation of the skull. Skull deformation may produce a local contusion or hemorrhage if the deformations of the tissues exceed their injury thresholds.
|
From page 65... ...
In these situations, linear acceleration is a reasonable surrogate for the brain tissue distortion response. By contrast, in the more common non-centroidal head impacts, linear and rotational accelerations are not correlated significantly, and the rotational acceleration component of the head response correlates most strongly with the average and peak brain deformations.
|
From page 66... ...
. Similarly, animal models that allow more head rotation after impact or enhanced head or brain movement produce more severe brain injuries (Foda and Marmarou, 1994; Marmarou et al., 1994)
|
From page 67... ...
In this section the molecular processes that have been shown to characterize brain injuries are discussed in the context of age and sex. It should be noted that much of what is currently known about these processes is drawn from research involving animals and subjects sustaining moderate to severe brain injuries.
|
From page 68... ...
. This model has been used in numerous age groups to generate diffuse brain injuries with measurable cognitive deficits, and mild fluid percussion injuries mimic numerous aspects of concussive injuries (Prins and Hovda, 1998, 2001; Prins et al., 1996)
|
From page 69... ...
ongoing) FIGURE 2-2 Neurochemical cascade observed after moderate traumatic brain injuries.
|
From page 70... ...
While it is thought that these events occur to a lesser degree or for a shorter duration following milder or concussive injuries, human studies examining acute neurochemical changes following concussive injuries in youth as well as adults or that address sex differences in response are lacking. Metabolic Cascade After Traumatic Brain Injury: Glucose and Cerebral Blood Flow The energy required to resolve the disruption of the neurochemical environment seen after injury triggers an immediate increase in brain glucose uptake or CMRglc.
|
From page 71... ...
appear to produce a more profound and longer-lasting depression than the more diffuse fluid percussion injury does (Prins and Hovda, 2009; Sutton et al., 1994)
|
From page 72... ...
Changes in Cerebral Blood Flow After TBI There have been hundreds of studies on changes in CBF after TBI, but relatively few of them have focused on CBF changes in pediatric populations, and even fewer have addressed changes following a concussion or mTBI. Only a couple of studies have evaluated sex differences in changes in CBF following TBI.
|
From page 73... ...
In summary, changes in brain glucose metabolism and blood flow after brain injury have been shown to be important biomarkers of TBI pathophysiology in all age groups and injury severities. However, there is a lack of data on changes in blood flow and glucose metabolism following mTBI and concussions in both males and females and at different ages during childhood and adolescence.
|
From page 74... ...
Thus, researchers have focused on the measurement of damage produced by free radicals by quantifying the lipid peroxidation, protein nitration, and DNA oxidation that occurs after moderate to severe TBI. In rodent models, increases in lipid peroxidation were observed 1 to 24 hours after weight drop injury (severity not always
|
From page 75... ...
While significant strides have been made toward understanding the effects of free radicals after more severe TBI, far fewer studies have addressed oxidative stress after mild or concussive injuries. Mild TBI produced decreases in cytochrome oxidase activity in the cortex and hippocampus 1 to 10 days after fluid percussion injury in adult rats (Hovda et al., 1991)
|
From page 76... ...
after TBI led to the use of APP as a marker of axonal injury. Positive APP labeling has been shown in adult animal models after mild fluid percussion injury (Hoshino et al., 2003; Hylin et al., 2013; Shultz et al., 2011)
|
From page 77... ...
Plasticity and Synaptic Changes TBI leads to changes in the connectivity of the brain and alterations in the intimate communication between synapses. Experimental models with adult moderate fluid percussion injury have revealed that synaptophysin (a protein within the synapse)
|
From page 78... ...
. Recovery of this plasticity response was observed when immature rats were placed in EE 2 weeks after mild fluid percussion injury (Giza et al., 2005)
|
From page 79... ...
The injury model produced no significant edema, hippocampal cell loss, change in cerebral volume, or axonal injury relative to shams, thus indicating the mild nature of the injury. The cumulative effect of cognitive dysfunction when injuries occur at shorter intervals suggests that the impact interval reflects the duration of cerebral vulnerability.
|
From page 80... ...
In this section, the risk factors for concussion as they pertain to the developing brain, including sex, age, genetics, and history of prior concussions, are addressed. A discussion of factors that influence concussion outcomes and recovery appears in Chapter 4.
|
From page 81... ...
. Relative to adults, children demonstrate more widespread and prolonged cerebral swelling and increased metabolic sensitivities following a head injury, and these physiological changes may result in more apparent (i.e., more severe and persistent)
|
From page 82... ...
. Brain injury models indicate that brain function may be altered for several days to weeks
|
From page 83... ...
FINDINGS The committee offers the following findings on the neuroscience, biomechanics, and risks of concussion in the developing brain: • There are normal changes in brain structure, blood flow, and me tabolism that occur with brain development that may influence susceptibility to and prognosis following concussions in youth. • Research primarily involving animals and individuals with more severe head injury has provided a limited framework for under standing the neuroscience of concussion.
|
From page 84... ...
1997. Cerebral hyperglycolysis following severe traumatic brain injury in humans: A positron emission tomography study.
|
From page 85... ...
2003. Cerebral blood flow in chronic symptomatic mild traumatic brain injury.
|
From page 86... ...
2006. Mild traumatic brain injury in children: Just another bump on the head?
|
From page 87... ...
2008. Mild traumatic brain injury to the infant mouse causes robust white matter axonal degeneration which precedes apoptotic death of cortical and thalamic neurons.
|
From page 88... ...
1999. The consequences of traumatic brain injury on cerebral blood flow and autoregulation: A review.
|
From page 89... ...
1996. Local cerebral glu cose metabolism in patients with long-term behavioral and cognitive deficits following mild traumatic brain injury.
|
From page 90... ...
2009. Incidence, risk, and protective factors of mild traumatic brain injury in a cohort of Australian nonprofessional male rugby players.
|
From page 91... ...
2007. Predictors for traumatic brain injuries evaluated through accident reconstruc tions.
|
From page 92... ...
2011. Cerebrovascular pathophysiology following mild traumatic brain injury.
|
From page 93... ...
2005. Mild traumatic brain injury induces persistent cognitive deficits and behavioral disturbances in mice.
|
From page 94... ...
2010. Repeat traumatic brain injury in the juvenile rat is associated with increased axonal injury and cognitive impair ments.
|
From page 95... ...
1995. Neurobehavioural dysfunction following mild traumatic brain injury in childhood: A case report with posi tive findings on positron emission tomography (PET)
|
From page 96... ...
2008. Investigation of traumatic brain injuries using the next generation of simulated injury monitor (SIMon)
|
From page 97... ...
2008. Cerebral blood flow and auto regulation after pediatric traumatic brain injury.
|
From page 98... ...
2013. Animal models of traumatic brain injury.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.