Abstract

The issue pertaining to the effect of multiple self-reported sports-related concussions on cognitive function is controversial. Although this topic has received increased attention in the literature recently, the issue remains unresolved. Evidence supporting a detrimental cognitive effect has been reported at a sub-concussive level and following one, two, and three or more previous concussions. However, numerous studies have been unable to replicate these findings. Additionally, discrepancies between neuropsychological testing formats have been identified, where studies utilizing traditional tests tend to support the notion of detrimental cognitive effects whereas studies with computerized tests have tended to demonstrate no effect. The present study sought to examine possible detrimental cognitive effects in a sample of adult male rugby union players who reported a history of three or more concussions (n = 34) compared with those who reported no previous concussions (n = 39). A computerized neuropsychological battery and a traditional neuropsychological measure of processing speed were administered for this purpose. Findings revealed that there were differences between groups on two processing speed measures from both traditional and computerized tests. Athletes with a history of multiple concussions performed significantly lower on these measures than those with no history of concussion. These results provide further evidence to suggest that a history of three or more self-reported concussions in active athletes may have a detrimental effect on cognitive function. Future research may focus on identifying moderating factors in an attempt to resolve some of the conflicting findings and identify potential athletes at risk for sustaining cognitive deficits.

Introduction

During the past decade, neuropsychological testing has increasingly formed an integral component of concussion management. Typically, the immediate and short-term effects of sports-related concussion include both physical symptoms and measurable cognitive deficits. These symptoms and deficits routinely occur in the absence of detectable neurological change and tend to resolve within 1 month post-injury (Iverson, Lovell, & Collins, 2005; Lovell, Collins, & Bradley, 2004; McCrory et al., 2009).

Although the acute effects of a single concussion have been detailed (Lovell, 2009), the effects of multiple concussions on cognitive function and the potential for long-term deficits remain poorly understood. Initial research tended to be focused solely on the acute effects, whereas the effects of multiple concussions and the potential for associated long-term and cumulative deficits have only more recently received increased attention (Broglio, Ferrara, Piland, & Anderson, 2006; Collie, McCrory, & Makdissi, 2006).

Chronic traumatic encephalopathy (CTE) or dementia pugilistica, as it was initially known, refers to the progressive neurological deterioration associated with athletes (particularly boxers) following repetitive brain trauma. Initial symptom presentation typically manifest as deterioration in attention, concentration, and memory, together with disorientation and confusion. Lack of insight, poor judgment, and overt dementia tend to occur with the progression of CTE (McKee et al., 2009). A recent review of neuropathologically verified CTE cases found that one third of athletes were symptomatic at the time of their retirement from sport (McKee et al., 2009), suggesting active athletes are not immune and the initial stages of the neurodegenerative process associated with CTE may manifest earlier than initially suspected.

The association between the self-reported history of concussion and current neuropsychological function remains controversial (Collie et al., 2006). Despite evidence for a prolonged recovery in athletes with a history of concussion compared with those with no history (Iverson, Gaetz, Lovell, & Collins, 2004a; Slobounov, Slobounov, Sebastianelli, Cao, & Newell, 2007), unequivocal support for the notion that long-term effects exist has not been forthcoming. Although some studies have reported results that support the notion that athletes with a history of concussion exhibit reduced cognitive performance relative to athletes with no history of concussion (Iverson et al., 2004a; Moser, Schatz, & Jordan, 2005), other studies have not replicated such findings (Broglio et al., 2006; Bruce & Echemendia, 2009; Collie et al., 2006; Iverson, Brooks, Lovell, & Collins, 2006).

Evidence is accumulating in support of the notion that three or more concussions may be associated with a detrimental effect in neuropsychological test performance (Guskiewicz et al., 2003). Further, some studies purport that athletes who have experienced three or more concussion are at an increased risk for future concussions (De Beaumont, Lassonde, Leclerc, & Theoret, 2007; Guskiewicz et al., 2003; Rabadi & Jordan, 2001) and are more likely to experience prolonged recovery from their next concussion (Guskiewicz et al., 2003; Slobounov et al., 2007). Despite this, a number of studies have not been able to replicate these findings (Bruce & Echemendia, 2009; Pellman, Lovell, Viano, Casson, & Tucker, 2004).

In general, few studies utilizing a computerized neuropsychological format have detected deficits (Iverson et al., 2004a) tending to support the notion that there are not long-term or cumulative cognitive deficits (Broglio et al., 2006; Collie et al., 2006; Iverson, Brooks, Lovell, & Collins, 2006; Straume-Naesheim, Andersen, Dvorak, & Bahr, 2005), whereas large-scale studies using traditional measures have generally demonstrated detrimental cognitive effects (Collins et al., 1999; Moser & Schatz, 2002; Moser et al., 2005; Wall et al., 2006). The discrepancy between results utilizing traditional versus computerized neuropsychological formats may be attributable to the differential reliabilities of the measures. Reliabilities for some scores on computerized measures have tended to be poorer than putative comparable traditional measures, whereas other research has questioned the reliability of computerized measures for detecting and monitoring sports-related concussion (Randolph, McCrea, & Barr, 2005).

To date, only one study appears to have attempted to provide some clarity on the discrepancy among neuropsychological testing formats. Bruce and Echemendia (2009) examined cognitive function among a large sample of male collegiate athletes with a history of nil, one, two, and greater than two self-reported concussions. They conducted three separate studies examining group performance on computerized measures alone, traditional measures alone, and then on both computerized and traditional measures. Results found no significant association between self-reported concussion history and performance on either neuropsychological format, strongly suggesting that a history of multiple self-reported concussions has little to no impact on long-term cognitive functioning among collegiate male athletes.

The aim of this study is to contribute to the growing literature concerned with the potential detrimental cognitive effects of multiple sports-related concussions. The current study examined the performance of a group of adult male rugby union players with a self-reported history of three or more concussions, with a group of well-matched adult male rugby union players with no history of self-reported concussions on a computerized neuropsychological test (ImPACT) and a traditional pencil and paper measure of processing speed (Wechsler Adult Intelligence Scale-3rd Edition [WAIS-III], processing speed index [PSI]). It was hypothesized that athletes with a self-reported history of three or more concussions, as a group, would reveal differences on one or more outcome measures from athletes with no self-reported history of concussions.

Materials and Methods

Participants

A total of 73 male rugby union players aged 19–30 years participated in this study, which was conducted during the preseason of 2009. Players with a self-reported history of three or more concussions (n = 34), but who had not sustained a concussion in the previous 3 months, were referred to the study by medical staff from three Sydney grade rugby union clubs (≥3 concussions group). Corroborative concussion data were not available for this study. As such athletes' self-report (via the ImPACT inventory) was the sole source of information pertaining to previous concussion history. Data were restricted to estimates of the dates for the athlete's five most recent concussions. Concussions were not medically documented. Concussive injury was defined as the presence of at least one of the following: (a) confusion or disorientation; (b) loss of consciousness for 30 min or less; (c) post-traumatic amnesia for less than 24 hr; and/or (d) other transient neurological abnormalities such as focal signs, seizure, and intracranial lesion not requiring surgery (Carroll, Cassidy, Holm, Kraus, & Coronado, 2004). A total of 39 well-matched adult male rugby union players, who had never received a concussion, were recruited via identical methods as the concussed group to the no previous concussion control group (no concussions group). The control group participants were matched on relevant variables such as gender, age, education, number of years of participation in rugby union, level of competition played, and position (forward vs. backline). The relevant university human ethics committee approved the study design and all participants provided their informed consent. There were no participants with a positive history of epilepsy, brain surgery, meningitis, substance use, learning disorder, or hyperactivity. Two participants in the three or more concussions group reported a history of depression (although neither were experiencing symptoms at the time of testing and neither were currently prescribed medication). There were no further reports of a history of any other psychiatric conditions. Nine participants (seven in the three or more concussions group and two in the no previous concussions group) reported a history of treatment for migraine. One participant (from the three or more concussions group) reported attending special education classes for reading and speech and repeated one or more years of school.

Materials/Procedures

The WAIS-III PSI was administrated as the traditional neuropsychological measure. The WAIS-III PSI is calculated with two subtests (digit symbol-coding and symbol search) and assesses skills of focusing attention and quickly scanning, discriminating between, and sequentially ordering visual information (Wechsler, 1997). The Wechsler Test of Adult Reading (WTAR) was administered to ascertain the estimated premorbid level of performance on the WAIS-III Full-Scale Intelligence Quotient (FSIQ) and PSI. The WTAR is a measure of reading ability that is used as an estimate of premorbid intellectual ability in individuals with cognitive dysfunction. Participants are asked to read aloud 50 phonetically irregular words of increasing difficulty. An estimate of intelligence is determined by the number of words correctly pronounced. The WTAR also provides a predicted composite score (e.g., predicted PSI) based on the individual's reading performance (Wechsler, 2001).

Version 6.0 of ImPACT was also administered. ImPACT is a brief computer administered neuropsychological test battery. It consists of six individual test modules which measure different aspects of cognitive function and contribute to four composite scores: verbal memory composite, visual memory composite, reaction time composite, and processing speed composite. An additional score, Impulse Control, is also calculated and used as a measure of test validity. The clinical utility of ImPACT has been assessed in a number of studies (Iverson et al., 2005; Iverson, Brooks, Collins, & Lovell, 2006). In addition to completing the demographic inventory, all participants were required to complete the post-concussion symptom scale from the ImPACT battery, which consists of 21 commonly reported symptoms (Lovell et al., 2006). Information from the demographic inventory pertaining to previous concussions is presented in Table 1.

Table 1.

Demographic information pertaining to previous concussions

Athlete number Age on testing (Yr:Mth) No. Prv Conc. Estimated days since five most recent concussions No. of Prv. Conc. resulting in
 
Total Games Missed Grade/ level of Comp. Years Pld. at this level Position 
    LOC Confusion Ant. Amn. Retro. Amn.     
26:3 7,137; 3,850; 2,023 Backline 
24:4 1,268; 964; 843; 478; 113 Backline 
20:9 1,429; 1,308; 1,064; 578; 293 Backline 
19:11 3,964; 2,503; 1,773; 798; 312 Forward 
25:4 918; 614; 523; 313 Forward 
21:2 702; 581; 283 Backline 
23:3 12 599; 524; 304; 195; 202 12 12 Forward 
21:3 569; 509; 283; 304 Forward 
23:11 536; 161; 175 Forward 
10 19:1 981; 737; 677; 312 Backline 
11 28:8 1,347; 982; 678; 617 Backline 
12 21:8 1,582; 1,521; 1,187; 822; 355 Forward 
13 21:9 1,712; 952; 707; 586; 252 Backline 
14 22:6 9,050; 8,745; 8,654; 8,320; 2,080 Forward 
15 20:4 1,715; 1,075; 589; 254 Forward 
16 21:7 1,711; 1,346; 707; 619; 312 Backline 
17 30:2 1,349; 1,014; 933; 345; 263 Backline 
18 23:9 1,705; 1,340; 975; 701; 610 Backline 
19 25:6 1,935; 1,205; 628; 506; 263 Backline 
20 24:11 1,691; 1,326; 1,051; 929; 686 Forward 
21 24:4 1,066; 945; 550; 375; 215 Forward 
22 21:7 13 1,529; 1,408; 1,074; 434; 313 Forward 
23 25:0 2,017; 1,652; 1,075; 953; 345 Forward 
24 19:8 923; 710; 589 Backline 
25 19:7 2,080; 1,350; 985; 620 Forward 
26 18:10 3,908; 3,543; 3,297 Forward 
27 23:8 2,299; 1,569; 815; 662; 438 Forward 
28 21:11 2,478; 1,748; 1,444 Forward 
29 24:5 1,352; 987; 622; 348; 227 20 Backline 
30 21:4 1,408; 1,287; 587; 240 Forward 
31 18:7 1,750; 1,385; 1,110; 989; 408 Backline 
32 21:7 1,126; 448; 337; 119 Forward 
33 24:3 10 1,689; 1,050; 594; 312; 200 Backline 
34 23:3 1,720; 990; 595 Forward 
Athlete number Age on testing (Yr:Mth) No. Prv Conc. Estimated days since five most recent concussions No. of Prv. Conc. resulting in
 
Total Games Missed Grade/ level of Comp. Years Pld. at this level Position 
    LOC Confusion Ant. Amn. Retro. Amn.     
26:3 7,137; 3,850; 2,023 Backline 
24:4 1,268; 964; 843; 478; 113 Backline 
20:9 1,429; 1,308; 1,064; 578; 293 Backline 
19:11 3,964; 2,503; 1,773; 798; 312 Forward 
25:4 918; 614; 523; 313 Forward 
21:2 702; 581; 283 Backline 
23:3 12 599; 524; 304; 195; 202 12 12 Forward 
21:3 569; 509; 283; 304 Forward 
23:11 536; 161; 175 Forward 
10 19:1 981; 737; 677; 312 Backline 
11 28:8 1,347; 982; 678; 617 Backline 
12 21:8 1,582; 1,521; 1,187; 822; 355 Forward 
13 21:9 1,712; 952; 707; 586; 252 Backline 
14 22:6 9,050; 8,745; 8,654; 8,320; 2,080 Forward 
15 20:4 1,715; 1,075; 589; 254 Forward 
16 21:7 1,711; 1,346; 707; 619; 312 Backline 
17 30:2 1,349; 1,014; 933; 345; 263 Backline 
18 23:9 1,705; 1,340; 975; 701; 610 Backline 
19 25:6 1,935; 1,205; 628; 506; 263 Backline 
20 24:11 1,691; 1,326; 1,051; 929; 686 Forward 
21 24:4 1,066; 945; 550; 375; 215 Forward 
22 21:7 13 1,529; 1,408; 1,074; 434; 313 Forward 
23 25:0 2,017; 1,652; 1,075; 953; 345 Forward 
24 19:8 923; 710; 589 Backline 
25 19:7 2,080; 1,350; 985; 620 Forward 
26 18:10 3,908; 3,543; 3,297 Forward 
27 23:8 2,299; 1,569; 815; 662; 438 Forward 
28 21:11 2,478; 1,748; 1,444 Forward 
29 24:5 1,352; 987; 622; 348; 227 20 Backline 
30 21:4 1,408; 1,287; 587; 240 Forward 
31 18:7 1,750; 1,385; 1,110; 989; 408 Backline 
32 21:7 1,126; 448; 337; 119 Forward 
33 24:3 10 1,689; 1,050; 594; 312; 200 Backline 
34 23:3 1,720; 990; 595 Forward 

Notes: No. = Number; Yr = Years; Mth = Months; Prv. = Previous; Conc. = Concussions; LOC = Loss of Consciousness; Amn. = Amnesia; Ant. = Anterograde; Retro. = Retrograde; Comp. = Competition; Pld. = Played.

Statistical Analysis

The data were analyzed with SPSS, version 17.0 for Windows. Between-group differences on demographic information were analyzed via univariate independent-samples t-tests. Multivariate analysis of variance (MANOVA) was used to examine overall differences between groups, with the four ImPACT composite scores, the symptoms checklist, and the PSI measures as dependent variables. A number of χ2 analyses were also conducted to examine if there were significant group differences between the frequencies of abnormal scores (defined as being >1.5 SD below the mean) on each of the outcome variables. The WTAR served as an estimate of premorbid general intellectual ability (predicted FSIQ) and as an estimate of premorbid processing speed (predicted PSI). These scores served as an estimated baseline for athletes as individual baseline data were not collected. That is, if an athlete's “actual score” was significantly lower than their “predicted score,” it was interpreted as demonstrating a decline in cognitive function.

Results

Two players from the three or more concussions group demonstrated a significant difference between actual PSI score and predicted PSI score. No player from the control group demonstrated a significant difference between actual PSI score and predicted PSI score. Univariate independent-samples t-tests revealed that there were no significant between-group differences for age, education, predicted FSIQ, predicted PSI, grade/level of competition, and years of participation at this level of competition. The results of this analysis are presented in Table 2.

Table 2.

Descriptive statistics for demographic data by group with t-test comparisons

 No concussions
 
≥3 concussions
 
Statistic p-value 
 Mean SD Mean SD   
Age (years) 23.90 3.54 22.79 2.65 t(71) = 1.49 .140 
Education (years) 13.36 2.74 13.79 2.33 t(71) = −0.73 .471 
Predicted FSIQ 102.49 7.98 102.93 7.35 t(71) = −0.55 .584 
Predicted PSI 101.08 6.15 101.15 5.94 t(71) = −0.05 .961 
Grade/level of competition 1.28 0.46 1.29 0.46 t(71) = −0.11 .911 
Years played at this level 2.97 1.74 2.94 1.92 t(71) = 0.08 .938 
Position played 22 Fwd 17 Bkl 19 Fwd 15 Bkl   
Number of Prv. concussions   5.24 2.44 Min. 3, Max. 13 
Days since Prv. concussion   560.94 671.82 Min. 113, Max. 3297 
 No concussions
 
≥3 concussions
 
Statistic p-value 
 Mean SD Mean SD   
Age (years) 23.90 3.54 22.79 2.65 t(71) = 1.49 .140 
Education (years) 13.36 2.74 13.79 2.33 t(71) = −0.73 .471 
Predicted FSIQ 102.49 7.98 102.93 7.35 t(71) = −0.55 .584 
Predicted PSI 101.08 6.15 101.15 5.94 t(71) = −0.05 .961 
Grade/level of competition 1.28 0.46 1.29 0.46 t(71) = −0.11 .911 
Years played at this level 2.97 1.74 2.94 1.92 t(71) = 0.08 .938 
Position played 22 Fwd 17 Bkl 19 Fwd 15 Bkl   
Number of Prv. concussions   5.24 2.44 Min. 3, Max. 13 
Days since Prv. concussion   560.94 671.82 Min. 113, Max. 3297 

Notes:SD = standard deviation; FSIQ = full-scale IQ; Fwd = forward; Bkl = backline; Min. = minimum; Max. = maximum; Prv. = previous.

MANOVA was used to examine overall differences between the no previous concussion group and the three or more previous concussion group. Pearson's correlation coefficients revealed moderate but significant correlations between age and the ImPACT visual motor speed composite (r = .311, p = .007) as well as the WAIS-III PSI (r = .253, p = .045). Furthermore, there were significant correlations between predicted FSIQ and all but one dependent variable (the symptoms checklist). Other variables including education and predicted PSI were not significantly associated with any of the outcome variables. Therefore, it was decided to include age and predicted FSIQ as covariates in the MANOVA.

The multivariate assumption of normality was violated for one of the dependent variables (total symptoms score), and a log-transformation was conducted. Homogeneity of the covariance matrix was maintained as indicated by Box's M; M = 34.35, F(21,17797.44) = 1.49, p = .070. Levene's tests were not significant for any of the outcome variables; therefore, the assumption of homogeneity of variances was upheld for all dependent variables. Parametric tests were used for both transformed and non-transformed data, and there was no observable difference between the results. For ease of interpretation, only the non-transformed data are reported.

Overall, multivariate tests revealed a significant difference between the two groups for at least one of the dependent variables controlling for age and predicted FSIQ; Wilks' Λ = 0.750, F(6,64) = 3.56, p = .004. Tests of between subject effects revealed the ImPACT visual motor speed—F(1) = 6.55, p = .013—and the WAIS-III PSI—F(1) = 5.26, p = .025—were the only dependent variables demonstrating significant between group differences. This indicates that athletes reporting no history of concussion performed significantly better as a group on these two measures than those with a history of three or more concussions. The results of this analysis are presented in Table 3. There were no significant group differences in the frequency of abnormal scores on any of the outcome variables. Frequencies of abnormal performance by group and the results of the χ2 tests are presented in Table 4.

Table 3.

Results of MANOVA by group

 No concussions
 
≥3 concussions
 
df Statistic p-value Effect size 95% confidence interval
 
 Mean SD Mean SD     Lower bound Upper bound 
ImPACT 
 Verbal Memory Composite 0.849 0.085 0.850 0.121 0.24 .876 0.01 −0.45 0.47 
 Visual Memory Composite 0.770 0.119 0.741 0.132 2.05 .157 −0.23 −0.69 0.23 
 Visual Motor Composite 43.05 7.14 39.36 6.01 6.55 .013* −0.55 −1.02 −0.08 
 Reaction Time Composite 0.554 0.071 0.526 0.052 1.32 .254 −0.45 −0.91 0.02 
 Impulse Control Score 4.41 3.54 8.65 5.74 5.35 .024* −0.88 0.40 1.36 
 Total Symptoms Score 4.64 6.10 6.38 10.11 0.56 .456 −0.21 −0.25 0.67 
WAIS-III 
 Processing Speed Index 111.38 13.00 106.50 10.11 5.26 .025* −0.41 −0.88 0.05 
 No concussions
 
≥3 concussions
 
df Statistic p-value Effect size 95% confidence interval
 
 Mean SD Mean SD     Lower bound Upper bound 
ImPACT 
 Verbal Memory Composite 0.849 0.085 0.850 0.121 0.24 .876 0.01 −0.45 0.47 
 Visual Memory Composite 0.770 0.119 0.741 0.132 2.05 .157 −0.23 −0.69 0.23 
 Visual Motor Composite 43.05 7.14 39.36 6.01 6.55 .013* −0.55 −1.02 −0.08 
 Reaction Time Composite 0.554 0.071 0.526 0.052 1.32 .254 −0.45 −0.91 0.02 
 Impulse Control Score 4.41 3.54 8.65 5.74 5.35 .024* −0.88 0.40 1.36 
 Total Symptoms Score 4.64 6.10 6.38 10.11 0.56 .456 −0.21 −0.25 0.67 
WAIS-III 
 Processing Speed Index 111.38 13.00 106.50 10.11 5.26 .025* −0.41 −0.88 0.05 

Notes: The ImPACT data represented in this table are raw scores. Memory composite scores are presented as percentage correct; visual motor and reaction time are presented as time in seconds; impulse control and total symptoms are presented as a cumulative total. The Processing Speed scores are standard scores. A negative effect size score represents inferior performance by the concussion group, conversely a positive score represents a superior performance by the concussion group.

*Significant at the .05 level.

Table 4.

Frequency of athletes performing at least 1.5 SD below the mean and results of the χ2 tests

 No concussions ≥3 concussions p-value 
Verbal Memory Composite .994 
Visual Memory Composite .460 
Visual Motor Composite n/a 
Reaction Time Composite 1.000 
Total Symptoms Score .240 
Processing Speed Index n/a 
 No concussions ≥3 concussions p-value 
Verbal Memory Composite .994 
Visual Memory Composite .460 
Visual Motor Composite n/a 
Reaction Time Composite 1.000 
Total Symptoms Score .240 
Processing Speed Index n/a 

Notes: n/a = not applicable, due to no score in either group falling 1.5 SD below the mean for these variables.

Pearson's χ2 test.

Fisher's exact test.

Discussion

This study has demonstrated that adult male rugby union players reporting three or more previous concussions demonstrate significantly reduced performance on a computerized measure of visual motor speed and a traditional measure of processing speed, compared with rugby union players with no self-reported history of concussion. Interestingly, despite finding no athlete from either group performed worse than 1.5 SD below the mean on the measures that demonstrated significant differences between the groups (i.e., PSI and visual motor speed), a significant difference between groups was observed on these variables, suggesting that these measures are particularly sensitive to the residual effects of sports-related concussion. Alternatively, this may in fact reflect a relatively subtle deficit on these two measures. Despite this, given the closely matched samples, these findings were interpreted as supporting the notion that there are detrimental cognitive effects of multiple concussions.

These results are consistent with previous research that demonstrated reduced performance on traditional neuropsychological measures of processing speed in a sample of rugby union players with a history of more than two concussions (Shuttleworth-Rdwards & Radloff, 2008). Moreover, the current results are similar to those reported by Gaetz, Goodman, and Weinberg (2000) who found reduced subjective information processing efficiency in athletes with a history of three or more concussions compared with athletes with no previous concussion history. These self-reported deficits were supported by significant differences between the groups on response latency measures. Collins and colleagues (1999, 2002) found that college American football players with repeated concussions performed worse on neuropsychological testing than those with no prior concussion and that high-school American football players with three or more concussions presented with more severe on-field concussion markers. Similarly, Iverson and colleagues (2004a) and Iverson, Gaetz, Lovell, and Collins (2004b) reported younger athletes with a history of multiple concussions reported significantly more symptoms and demonstrated a trend toward lower memory scores at baseline.

These results have potential implications for the clinical management of concussed athletes. Accumulating evidence suggesting there may be long-term effects of sports-related concussion, in conjunction with the well-established notion that the concussed brain is increasingly vulnerable to further, more severe, and longer lasting sequelae (Cantu, 2003; Echemendia & Cantu, 2003; Guskiewicz et al., 2003) and current research that has speculated that recently sustained concussion may be a significant predictor for recurrent concussion (Hollis et al., 2009), provide important information to the athlete, their family, and the sports physician for making informed decisions regarding the risk of ongoing participation in contact sports.

The current results differ from those attained by a recent similar large-scale study examining male collegiate athletes (Bruce & Echemendia, 2009). Bruce and Echemendia (2009) did not find a significant association between self-reported concussion history and performance on either computerized or traditional neuropsychological tests. The authors concluded that athletes who report a distant history of concussion have minimal enduring neurocognitive deficits. The discrepancy in the findings may have occurred as a result of the number of concussions sustained by athletes. In our study, athletes in the three or more concussion group sustained an average of 5.24 concussions. This may represent a greater incidence of concussion than that observed in the more than two concussions group in the Bruce and Echemendia study, which would likely account for the different results.

Although our group data indicated that there does appear to be a detrimental effect on cognition, it is recognized that, at the individual level, there are some players who are not demonstrating cognitive changes as a result of a multiple concussion history (Collie et al., 2006).

Unequivocal support in favor of the notion that there is a detrimental cognitive effect of multiple sports-related concussions has not been established. More recent studies have not found an association between a history of self-reported concussion and current neuropsychological test performance for both computerized and traditional neuropsychological measures (Broglio et al., 2006; Collie et al., 2006; Iverson, Brooks, Lovell, & Collins, 2006; Pellman et al., 2004). Further prospective research is required before definitive conclusions pertaining to potential detrimental cognitive effects of sports-related concussion can be established. Although the debate surrounding the effects of multiple concussion history is far from resolved, the current findings add further support to the notion that a history of multiple self-reported concussions has a detrimental effect on cognitive functioning among active athletes.

An important limitation of this study is the reliance on self-report information regarding the number of previous concussions in the absence of corroborative information. Additionally, data pertaining to the severity and the temporal relationship of the prior concussions were not available. Previous research has implicated concussion severity as contributing most to current deficits, whereas multiple concussion history exacerbated these deficits (De Beaumont et al., 2007). Moreover, concussions in rapid succession have been shown to be associated with increased vulnerability to more cumulative deficits (Gaetz et al., 2000). Further, due to the nature of the recruitment process (the inclusion and exclusion criteria based on the number of previous concussions) and the information regarding the study participation consent forms, athletes were aware, to some extent, of the study hypothesis. This was less than ideal but unavoidable and may have resulted in an expectancy effect, thus contributing to some of the observed results.

The results demonstrated that only one of the four composite scores for the computerized battery revealed a significant difference between groups, whereas the only traditional measure utilized detected a significant difference. These results may be partially or completely explained by differential reliabilities of the measures for detecting residual cognitive deficits following sports-related concussion.

Decline in cognitive function many years after concussive injuries, such as those commonly cited in boxers with CTE, suggest long-term consequences may be more prominent in later-life (Guskiewicz et al., 2005; Lovell, 2009). Multiple concussion history may exacerbate deficits associated with normal aging brain degeneration or activate early onset of neurodegenerative disease. Recent research on retired professional footballers with a history of three or more self-reported concussions found that they were more likely to be diagnosed with preclinical Alzheimer's-like disease, mild cognitive impairment, and experience significant memory problems compared with retired professional footballers with no concussion history (Guskiewicz et al., 2005; McKee et al., 2009). Further prospective research examining both active and retired athletes is warranted.

A number of potential moderator variables have previously been proposed that may impact on cognitive function following concussion. For example, the long-term consequence of multiple concussions may differ contingent upon the severity of the concussion, time lapse between concussions, age at injury, premorbid cognitive reserve, history of learning disability, genetic predisposition, or other unidentified risk factors (Bruce & Echemendia, 2009; Field, Collins, Lovell, & Maroon, 2003). Future studies should seek to attain such variables. At this point further research into the effects of multiple concussions is required to establish scientifically validated and clinically appropriate management standards for return-to-play decisions.

Funding

Supported by Macquarie University Postgraduate Research Fund.

Conflict of Interest

None Declared.

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