Sports-Related Concussion: New Frontiers in Neuroimaging
Jamie E. Pardini, PhD, Mark R. Lovell, PhD, and Andrew Wroblewski, PhD
Recently, our understanding of sports-related concussion (SRC) has been enhanced through the implementation of research exploring the impact of the injury on physiological correlates of brain functioning. Particularly, functional MRI, PET, SPECT, and electrophysiological studies have provided insight into potential long-term and short-term sequelae of the injury that extend beyond descriptions of the symptomatic and cognitive impairment that mild brain injuries can produce. This is especially helpful, given that a concussion cannot be detected using traditional neuroimaging procedures, such as magnetic resonance imaging (MRI) or computerized axial tomography (CT scan). fMRI and SRC
To date, functional magnetic resonance imaging (fMRI) research has provided insight into the physiological consequences of SRC. Across research studies, changes in brain activation are observed in even mild cases of SRC, either when compared to controls (e.g., Chen et al., 2004; Jantzen et al., 2004) or pre-injury baseline neuroimaging (e.g., Jantzen et al., 2004). Patterns of activation on fMRI are often related to cognitive dysfunction on neuropsychological testing (e.g., Lovell et al., 2007; Chen et al., 2007). However, in many fMRI studies, even when concussed athletes’ performance on in-scanner cognitive tasks is equivalent to that of control athletes, they continue to demonstrate differential activation patterns, both diffusely and within specific regions of interest (e.g., Chen et al., 2004; Chen et al., 2007; Lovell et al., in press; Jantzen et al, 2004). Figure 1 depicts activation from a sample of concussed athletes, and Figure 2 illustrates a case example of concussion-related hyperactivation and resolution of hyperactivation with recovery from concussion in a motocross athlete, along with an example of typical activation in a control athlete. Furthermore, extent of hyperactivation in concussed athletes has recently been found related to clinical recovery time in one study (Lovell et al., 2007). In this sample of athletes who underwent fMRI scanning approximately 1 week after concussion, athletes who exhibited the greatest degree of hyperactivation took significantly longer to recover, when compared to the rest of the sample. fMRI and SRC studies have also examined the relation between functional activation and symptom status. Correlations between post-concussion symptoms and activation have been observed in concussed athletes (Chen et al., 2007; Lovell et al., 2007; Pardini et al., 2006). Recent research using athletes who had experienced “complex concussions” (as defined by Concussion in Sport Group 18 BRAIN INJURY PROFESSIONAL
at the 2004 Prague Conference; McCrory et al., 2005) and continued to experience symptoms at least 1 month, and on average 5 months, post-injury, found differences in task performance and functional activation when comparing athletes reporting low levels of post-concussion symptoms to those reporting moderate levels of symptoms (Chen et al., 2007). Overall, results of this study indicated that athletes with complex concussions and moderate levels of post-concussion symptoms were more inaccurate and slower on cognitive tasks, and demonstrated reduced activation in the frontal lobes while performing working memory tasks. Although athletes with lower levels of post-concussion symptoms demonstrated no differences in performance on cognitive testing when compared to a control group, they did show reduced activation in the prefrontal regions when compared to control athletes. Similarly, Lovell et al. (2007) found that lower activation in a posterior parietal network of brain regions while completing a working memory task was associated with higher report of cognitive and somatic symptom clusters in recently concussed athletes (mean 6.6 ± 4.7 days post-injury). Current research also suggests that, while an athlete is still experiencing symptoms of concussion, the brain may recruit regions outside of those typically associated with task performance in an un-injured brain (Chen et al., 2007; Pardini et al., 2006). This may represent a compensatory physiological mechanism for the successful completion of working memory tasks while the brain is injured. Electrophysiological data and SRC
In addition to fMRI, electrophysiological studies have demonstrated differential activation in concussed versus non-concussed athletes. Electroencephalographic abnormalities have been observed in athletes with concussion and mild head injury (e.g. Korn et al., 2005; Slobounov et al., 2002). Studies using eventrelated potentials have shown attenuated P300 (Gosselin et al., 2006; Lavoie et al., 2004), N1 (Gosselin et al., 2006), and P2 (Gosselin et al., 2006) amplitudes in symptomatic concussed athletes when compared to control athletes. Lavoie et al., 2004 found that symptomatic concussed athletes also demonstrated reduced P300 amplitudes when compared to asymptomatic concussed athletes. In contrast, the Gosselin study (2006) found that asymptomatic concussed athletes had reduced P300, N1, and P2 amplitudes when compared to control athletes. Furthermore, symptom severity was inversely related to P300 amplitude (Lavoie et al., 2004). Also, athletes with histories of 3 or more concussions demonstrated longer P300 latencies when