A concussion is a form of traumatic brain injury resulting from forceful contact to the head. Although concussions can be sustained by many individuals, such as car accident victims and combat soldiers, concussions in athletes are especially common due to the vast amount of physical contact during the game. If an athlete receives forceful contact to the head and subsequently loses consciousness, it is very likely the athlete has sustained a concussion and assessment is just for confirmation. However, there may be instances in which forceful contact was exerted on the head, but the aforementioned symptom was not shown by the athlete. This does not necessarily mean the athlete escaped from the contact concussion-free, rather these situations illustrate the difficulty in detecting a concussion as both the athlete and team physician are likely unaware of a concussion. To complicate the problem of detection, concussions do not appear to show any structural abnormalities and thus, use of X-ray computed tomography (CT scan) would not aid in the assessment process. However, the athlete may experience balance problems and changes in reaction times and behaviour. Acknowledgement of these symptoms has led to the creation of assessment tools that allow medical professionals to detect differences in these variables, among other symptoms, from the athlete’s baselines. The Sport Concussion Assessment Tool (SCAT2), which tests a variety of domains including cognition, balance, and memory, has been the most widely used test in determining the presence of a concussion. Although SCAT2 is a comprehensive assessment, current research has sought to improve SCAT2 through the development of assessment tools yielding quicker and more accurate results.
Table of Contents
1. Rapid and objective assessments
1.1 Sport Concussion Assessment Tool (SCAT2)
Collaboration of medical professionals and concussion experts at the 2nd International Conference on Concussion in Sport in 2004 helped to develop the Sport Concussion Assessment Tool (SCAT). SCAT revolutionized the field of concussion assessment by combining a variety of concussion tests into a single tool to examine the symptoms, memory, and concentration of an athlete suspected of a concussion. However, SCAT was criticized for two major reasons. Firstly, SCAT did not contain a balance test and secondly, no method was in place to standardize the SCAT scores obtained from the test. These issues encouraged the development of SCAT2 at the 3rd International Conference on Concussion in Sport in 2009 which included a balance test and standardized scores to fully assess the symptoms, consciousness, and cognition of the concussed athlete. The purpose of SCAT2 is to quickly assess on the sidelines of the playing field whether a player is concussed. For portability, SCAT2 is printed on pocket cards and is clearly labeled for a medical professional to administer in sequential steps thereby formulating a score from 1-100, based on the responses and symptoms obtained from the tests, where lower scores represent poorer performance. SCAT2 contains a variety of diagnostic tools including: presentation of symptoms (ex: amnesia, dizziness, fatigue, sensitivity to light), memory function of recent events, balance testing during a tandem stance, and cognition testing (ex: naming the months of a year backwards).Although SCAT2 offers a comprehensive test for impairment of various functions, SCAT2 is only useful if the medical staff has access to the player’s baselines. Research on SCAT2 has shown differences in gender, age, and history of concussion; males, 9th graders (compared to 12th graders), and athletes who suffered a previous concussion performed worse on SCAT2. Considering that numerous athletes do not have baseline data, suggestions for the development of normative data relative to gender, age, and sport being played has gained attention for the further development of SCAT2.
1.2 King-Devick test as a quicker alternative to SCAT2
Although SCAT2 offers a comprehensive concussion assessment, SCAT2 still requires a lengthy period of time (approximately 20 minutes) to administer. Thus, it is suited more as a locker room assessment as opposed to an on-field test. King and colleagues showed how the King-Devick (K-D) test could be used as a quick and portable indicator of concussion during a rugby game. The K-D test measures the speed of eye movements as the player reads a series of numbers scattered across a card as fast as possible. The K-D test helps to detect impairment in eye movements and attention indicating damage to brain functions and areas, such as the brainstem., Compared to SCAT2, the K-D test takes only 2 minutes to administer and the athlete’s results are easy to interpret as concussed players have longer response times (≥5 seconds) compared to their own baselines (taken at the beginning of the season or pre-game when it is assumed the player is concussion-free). Current research on the validity of the K-D test show that it is sensitive enough to detect unwitnessed concussions including players who showed no concussion symptoms, albeit the difference in reaction times from pre- and post-game (4.4 seconds) did not meet the threshold typically indicating the presence of a concussion.
1.3 Static and dynamic balance testing
The use of balance testing in various concussion assessment tools indicates that balance is greatly affected in players who are suspected of a concussion. However, the majority of assessment tools only examine whether the player, at rest, can remain in an upright posture (i.e. static balance) and neglect to examine balance when the player is in motion (i.e. dynamic balance). Schneiders and colleagues used various exercise intensity regiments (rest, medium, and high intensity) in order to display impairments of static and dynamic balance in concussed athletes. The use of a single-leg stance defined static balance where athletes were required to stand as long as possible on one foot. Tandem gait was used as a measure of dynamic balance where athletes walked a straight 3m path using a heel-to-toe pattern.Relative to rest, the greatest impairments were seen in athletes who performed a high-intensity workout, consisting of cycling and arm cranking, as both stance and gait performance decreased after the exercise regime. Athletes who performed a medium-intensity workout, which consisted only of cycling, only saw impairments with decreased duration in the leg stance but not impairments in gait. Schneiders and colleagues believe tandem gait would be a more accurate form of assessment as gait examines the impairment of postural control in greater detail as opposed to leg stance which has a low test-retest reliability likely due to potential distractions from the environment. There is increasing evidence that balance can detect concussions with high accuracy. Mulligan and colleagues is one example who reports numerous cases of college football players who suffered balance deficits 48 hours after a game even if concussion was not clinically diagnosed. These results suggest that changes in balance are sensitive enough to detect unwitnessed and subtle concussions during the game and offer evidence that balance should be used more frequently as a leading assessment tool.
1.4 Measuring changes in simple reaction time
Advancements in technology have led to the movement of measuring reaction time on computers and other electronic devices. However, these electronic tools are not always as portable nor as affordable for low-budget teams, such as community recreation leagues. As a result, Eckner and colleagues developed a method that measures clinical reaction time (RTclin) by having athletes grasp with their dominant hand a falling rod as fast as possible. By using the values of gravity (a = 0.5gt2) and the distance the rod fell (d), medical professionals can determine the reaction time (t, in milliseconds) using the equation t = √d/a. The objective is to determine an athlete’s baseline reaction time and compare this value to the athlete’s reaction time after head contact. By subtracting the baseline value from the follow-up reaction time, medical professionals can confidently determine if the player had any significant change in their reaction time as positive scores indicate the likelihood of a concussion. Although concerns may arise for the accuracy in detecting precise changes in reaction times, Eckner and colleagues carried out data analysis to show that clinical reaction time is sensitive 75% of the time in detecting concussions which is respectable among other testing methods, such as the Standardized Assessment of Concussion (SAC) and Immediate Post-concussion Assessment Cognitive Test (ImPACT).
2. Preliminary studies involving structural or functional imaging
2.1 DTI as a detector of alterations to white matter integrity
Diffusion tensor imaging (DTI), which involves the imaging and analysis of white matter tracts in patients, has recently garnered attention as a technique for concussion assessment. Virji-Babul and colleagues compared white matter changes in adolescent athletes with and without concussion by measuring fractional anisotropy and mean diffusivity values. Fractional anisotropy (FA) refers to the direction of diffusion of water molecules while mean diffusivity is the amount of “freedom” in which water molecules can move. Virji-Babul et al. noticed that adolescents who sustained a concussion had an increase in FA values in conjunction with a decrease in mean diffusivity values. Research by Bazarian and colleagues showed how increasing numbers of concussion leads to greater differences in pre- and post-FA values which was measured before and after a 3-month high school hockey or football season. These results indicate that an increasing percentage of white matter becomes altered after each subsequent concussion an athlete receives. Although these studies provide convincing evidence for the presence of changes in white matter of concussed athletes, not all DTI research on concussions support these findings. Research by Levin et al. and Bashir and colleagues both suggest that the white matter integrity in individuals who suffered a concussion was no different from healthy individuals. Levin and colleagues believe that concussion severity and types of functional impairments differ between individuals and on a case-by-case basis. Thus, Levin et al. remain open to the idea that white matter changes may occur in concussed individuals, however, they clearly state that it is not for certain that white matter changes will be observed.
Regardless of whether DTI changes are indeed observed, it is important to note that most studies look at the white matter tracts before and after a defined time period. Few studies, if any, study white matter tracts immediately after a player receives a concussion indicating that DTI is more useful to determine the long-term changes of concussions along with players who may have received a concussion unknowingly in the past. DTI does not appear to be meant for “instant” assessment as white matter tracts likely change over the course of weeks to months instead of a matter of days.
2.2 MEG virtual recording senses over-activation of specific brain regions
A critical component of the present Neurowiki is to discuss emerging alternatives to “traditional” techniques used in concussion detection. Although neuroimaging methods have dominated in other realms of neuroscience research, including learning, memory, and addiction, it would seem fitting that the use of neuroimaging would be an effective tool in the detection of concussions. However, the majority of assessment tools rely on the use of symptom reporting, reaction times, or neuropsychological testing. The neglect of neuroimaging techniques is due, in part, to the inability of brain imaging tools to detect structural abnormalities. Further complications may include the high costs associated with the use, recruitment of skilled technicians, and maintenance of neuroimaging equipment if these techniques were to ever become commonplace in clinics. Despite these obstacles, researchers with an interest in brain imaging have devoted large amounts of research time and effort in pioneering neuroimaging tools that can accurately detect concussions. In particular, this Neurowiki will review and analyze the efforts of Tormenti and colleagues with research on a novel method known as magnetoencephalographic (MEG) virtual recording.
Tormenti and colleagues recruited 10 participants to complete a recognition task while an MEG recording machine measured response times and brain activation. Participants read a 5-word sentence at their own pace by pressing a button using their index finger to present the following word in each sentence. After presentation of the entire sentence, an object appears on a screen with a fixation point; the job of the participant is to determine if the location of the object matches the sentence. For example, participants will be shown the sentence “The green square is above” and depending on the image shown, participants must determine if the sentence and object location matched.
Results from Tormenti et al. show that concussed patients took longer to read the 2nd, 3rd, and 4th words in each sentence compared to healthy volunteers. In addition, concussed patients demonstrated a “fatigue effect” where concussed patients had longer response times in subsequent trials compared to their own response times in the beginning trials and when compared to healthy participants having finished the same number of trials. In terms of MEG activation, Tormenti and colleagues found that brain regions, particularly the occipitoparietal and temporal regions were overactive in concussed athletes. The brain activity in these regions combined helped to correctly assess whether the patient was concussed or not in 8 of 10 participants. This data has major implications in the field of neuroimaging
as MEG virtual recording appears to be quite accurate in concussion detection.
Despite these promising results, a major downfall of the proposed technique is the inability for all clinics or medical professionals to gain access to a MEG machine if indeed MEG virtual recording becomes a mainstream and reliable assessment tool. Issues of cost and the process of transferring knowledge to medical professionals for proper use of MEG virtual recording remain as the largest obstacles. Nevertheless, the work of Tormenti and colleagues help to advance both neuroimaging applications along with the field of concussion assessment as a whole. The development of MEG virtual recording provides medical professionals another tool to combat issues of detecting concussions from subtle or unnoticed head contact.
3. Use of neuropsychological (NP) testing for concussion assessment
3.1 ImPACT as a standard NP test
Analogous to SCAT2, the Immediate Post-concussion Assessment and Cognitive Test (ImPACT) is the most widely used neuropsychological (NP) test for concussions. Although ImPACT and SCAT2 both share a reputation of being the “standard test” that medical professionals use, the contents within ImPACT differ considerably from SCAT2. ImPACT emphasizes the testing of cognitive impairments associated with a concussion and thus requires more time to administer than SCAT2. In particular, ImPACT primarily measures visual and verbal memory along with processing speed. Schatz and Sandel recruited athletes suspected of a concussion in order to complete an online version of ImPACT; results showed that concussed athletes had less impulse control and reduced verbal memory.
Besides from being able to detect cognitive impairments in athletes, a major advantage in using ImPACT is the ability for this test to detect concussions in athletes who may try to hide their concussion through 'sandbagging'. The term ‘sandbagging’ refers to athletes who intentionally do a poor job on their baseline tests such that when an athlete does receive a concussion, impairment resulting from the concussion would not fall below baseline and thus, the athlete is not suspected of a concussion.Erdal tested this theory by asking participants to intentionally do worse on baseline tests to see if the test validity indicators within ImPACT could detect sandbagging. The results offered a satisfactory outcome; even when participants who were motivated and instructed to perform poorly on baseline tests, 90% of individuals were caught by the validity indicators set up in ImPACT. This suggests that ImPACT is an effective assessment tool that can not only detect sandbagging but can act as a useful tool in detecting concussions with high validity.
3.2 Virtual reality to detect attention deficits
The use of virtual reality has recently emerged in the past few years as an assessment tool for concussions. Creation of a virtual reality allows athletes to notice impairments in their everyday activities as they proceed through a typical day. Participants wear a head-mounted device that projects virtual images directly in their field of vision while head motion is simultaneously recorded. Prior research by Slobounov and colleagues have shown that virtual reality can detect impairments in balance and visual-kinesthetic learning in concussed athletes.
Nolin et al. extends previous findings through the application of virtual reality in testing inhibition and attention. By submerging participants into a virtual classroom filled with distractions, such as students talking and bells ringing, participants were to focus on a given task. This task consisted of letters appearing in front of participants who were required to press a button whenever the letter “K” followed the letter “A”. Results from Nolin et al.’s study showed that concussed athletes took longer to complete the task compared to healthy controls. These results indicate that concussed athletes have greater difficulty concentrating on tasks and inhibiting distractions within the environment. Furthermore, Nolin and colleagues report that concussed athletes experience greater cybersickness from virtual reality relative to controls. All of these impairments point to the high sensitivity in using virtual reality for accurate detection of concussions. Although more research is required for the applications of virtual reality, the greater sensitivity and high validity of the results make the use of virtual reality a promising new tool in concussion assessment.
4. Detecting concussions from the past
4.1 Olfaction discrimination declines over time from concussion
The majority of concussion assessment tools involve the use of brain imaging, change in reaction time, or cognitive impairment. All three branches of assessment attempt to detect concussion at the initial stages to prevent the athlete from returning to play and possibly worsening the concussion. However, the accuracy of these assessment tools is not 100 percent; thus, a concussion may still go undetected despite using an objective measure for concussion. Fortunately, research has begun to focus on detection methods that bypass the use of brain imaging or reaction times with the aim of testing another sensory modality which may be impacted from a concussion.
The Sniffin’ Sticks Inventory Tool (SSIT), which contains an odour list of 16 “common odours”, including coffee and fish, was used by participants to identify which of 3 odours presented was different. Results from the study showed a decline in odour identification, but not in odour sensitivity, as the length from the player’s last concussion increased over time. It is believed that damage to the frontal brain regions may cause long-term degenerative effects on more complex functions, such as odour discrimination, but not in more simpler functions, such as acknowledgement of an odour.
Although this research offers promising results, it is important to note that the use of olfaction discrimination in concussion assessment is still in the beginning stages. A downfall of this olfaction test was the inability to detect whether an athlete received one or multiple concussions in the past; this method could only crudely detect whether a player received a concussion or not. In addition, this method does not take into account individual differences in odour identification; past research has shown that females are better at odour identification compared to men while individuals who prefer certain odours, such as custard, can better discriminate these particular odours relative to individuals who do not show preference for that particular smell, like custard.