Indeed, even in those investigations that do detect a deficit, there seems to be little consistency in which cognitive performance is impaired Tellier et al. Inconsistency and variability between previous studies on long-term cognitive performance after mTBI is likely to be due to a combination of the variety of tasks used and the distinct samples tested. A variety of different aspects of cognitive performance have been investigated in the long-term after mTBI, using a number of different tasks. More importantly, tasks assessing the same cognitive function have varied in their difficulty, possibly leading to the inconsistent results.
A challenging cognitive task may be required to observe the subtle long-term alterations in participants with mTBI Segalowitz et al. Of particular utility in this regard are tasks that can be parametrically increased in difficulty Braver et al. However, few of the previous studies have used a range of difficulties within PVSAT to assess cognition.
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In addition, sampling of a mTBI population is challenging, as there is inherent heterogeneity between individuals Shum et al. Studies that have split their mTBI sample by PCS diagnosis have been relatively more consistent in their findings of cognitive deficit Cicerone and Azulay, ; Kumar et al. PCS is the term for the range of cognitive, somatic, and affective symptoms usually reported by participants after a mTBI Ryan and Warden, Symptoms typically resolve within 3 months Korinthenberg et al.
Long-term effects of mild traumatic brain injury on cognitive performance
Post-concussion-like symptoms have also been reported in healthy participants at levels that would result in PCS diagnosis in a head injured population Chan, ; Iverson and Lange, ; Wang et al. Furthermore, symptoms such as memory and concentration problems have been shown to emerge during the early recovery phase rather than forming the initial symptom complex Dikmen et al. It has been shown that subjective symptom report does not relate to objective symptoms Nolin et al. However, the use of adequate control populations can help alleviate some of the problems associated with the non-specificity of PCS.
Previous studies have used specific clinical populations such as those with post-traumatic stress disorder PTSD , chronic pain, and patients with equivalent injuries to the body, sparing the head Bell et al. It is also possible to control for post-concussion-like symptoms in healthy participants by splitting this group by PCS in a similar way to those with mTBI. Cognitive differences between these two groups may then be attributed to the report of PCS after mTBI, and not the symptoms alone.
Furthermore, if PCS is induced to some extent by damage at the time of injury, then it can be assumed that those mTBI participants with greater symptoms will perform worse on cognitive tasks, whereas there will be no correlation between performance and symptoms in control participants. Based on the considerations above, the present study investigates working memory and information processing speed in participants a year or more post-mTBI compared to a non-head injured control population.
These four groups were used to test the hypothesis that only participants who report persistent PCS after mTBI will show a cognitive deficit. In contrast, head-injured individuals who report no on-going PCS symptoms, and those without prior head injury regardless of extent of post-concussion symptoms are likely to have no evidence of cognitive dysfunction.
Furthermore, the cognitive deficit in mTBI participants with PCS will become more apparent as the difficulty of the task is parametrically increased. The study specifically aimed to recruit persons who had not sought medical attention following their mTBI.
Consequently, participants were recruited from a database generated by a previous study Dean et al. This survey was open to both those with and without head injury, and recorded demographic information, comprehensive details about any prior head injury in order to determine whether any injury met the diagnosis criteria for mTBI , and questionnaires on PCS and co-variables as detailed below. Those reporting any form of head injury in the survey were subsequently screened for mTBI according to ICD criteria. The study protocol was given a favorable opinion by the University of Surrey Ethics Committee.
Written informed consent was obtained prior to participation. A case history was taken which included a description of the injury, the date of injury, any other head injuries as well as general health and lifestyle information. Only participants at least a year post-mTBI, with no report of litigation, major invasive head injury, chronic pain, or other neurological conditions were contacted to take part in the study. Control participants were selected as those who did not report any prior head injury. We diagnosed PCS using the modified DSM-IV criteria specified by Mittenberg and Strauman , which requires report of three or more of the following symptoms subsequent to head trauma: 1 headache, 2 vertigo or dizziness, 3 irritability or aggression on little or no provocation, 4 anxiety, depression, or affective instability, 5 becoming fatigued easily, 6 disordered sleep, 7 changes in personality, and 8 apathy or lack of spontaneity.
Once diagnosed, selected participants were then asked to take part in computer-based tasks of memory and mental agility. The groups were:. Shaded gray boxes indicate groups generating the significant difference as revealed by Bonferroni-adjusted pairwise comparisons. Both tasks looked identical: single digit numbers between 1 and 9 inclusive were presented on the screen one at a time, with 60 of these stimuli including 20 randomly ordered target stimuli per block. There was a total of 12 blocks for each task, with 3 randomly ordered repetitions of the 4 levels of difficulty.
The keys M and C on a standard keyboard were counterbalanced as target and non-target response buttons across the participants. There were four conditions: 0-Back, 1-Back, 2-Back, and 3-Back. The numbers were presented every 3 s. Participants were asked to press the target button when the number on screen matched the number observed one previous 1-Back , two previous 2-Back , or three previous 3-Back.
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For every other number that did not match, participants were asked to press the non-target button. In the fourth condition 0-Back a random number between 1 and 9 was designated as a target at the beginning of the block. Performance on the 0-Back condition should be near ceiling for all participant groups, and was therefore used as a test of performance validity. There were four conditions: 2. The inter-stimulus interval ISI was 2. Each of the four ISI's was presented with each of the three target numbers. Participants were required to add the number on screen to the previously presented number.
At the beginning of each block they were given a target number of 9, 10, or Paired samples t -tests were performed for each of the groups to assess the difference between KSS Pre and Post. Only those co-variables which significantly differed between groups were used in the analysis. Correction for multiple comparisons was used, with a modified threshold p -value of 0. There was no significant difference between the groups on any of the demographic data age, gender, IQ.
However, the two groups without PCS had borderline scores, suggesting a generally poor level of nocturnal sleep in the sample. However, in the 2. No significant correlations with cognitive performance were observed in control participants for any co-variable. Error rates refers to average error rates across all conditions for each task n-Back average does not include 0-Back.
Shaded dark gray boxes indicate significant correlations after multiple comparison correction; light gray boxes indicate correlations that approach significance. The latter allows a tentative dissociation of the effect of PCS symptom report subsequent to mTBI on cognitive performance from the influence of post-concussion-like co-variables observed in non-head injured populations. It was assumed that the cognitive deficit would be relatively subtle, and only become apparent when task difficulty is high.
However, many previous studies have not accounted for PCS diagnosis, potentially masking cognitive impairments in a proportion of participants with mTBI. Therefore, not taking PCS into account leads to the more subtle results we expected, with only the more difficult levels differentiating between groups.
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These results suggest that accounting for PCS diagnosis may help reduce the variability inherent to mTBI, and create more consistent results in future research. An important aspect of the results was that all participant groups performed near ceiling on the 0-Back condition, and there was no significant difference in error rate. This condition was used as an indication of performance validity, and the result suggests this is unlikely to have significantly contributed to the differences observed for working memory and information processing speed.
As such, it is possible that this test may not be able to detect poor effort in the symptomatic group. However, participants had no overt incentive for poor effort, as they had been screened for any litigation and on-going chronic pain. Previous studies have suggested that participants without overt incentives for poor effort only fail standardized effort tests in a small proportion of cases Kemp et al. This could be due to there being no difference in effort in these groups, due to the difference being so slight that it is not detectable, or due to the standardized tests not being suitable for detecting effort in this population.
Performance on this task could also be influenced by iatrogenic factors, such as expectation of symptoms after injury or diagnosis, leading to differences in effort. However, participants did not know whether they were in the group with or without PCS, and without such categorization participants are less likely to be influenced by iatrogenic factors in relation to PCS. Participants could be influenced by expectation of symptoms after mTBI, but both mTBI groups would be equally influenced.
Therefore, if there is an effect of poor effort in this study which is not detected by the 0-Back, then it is likely to be small, and unlikely to be the sole cause of the large deficit observed in cognitive performance. The cognitive deficit seen in those participants with persistent PCS after mTBI may be due to a variety of underlying changes after injury. One putative mechanism which has begun to be explored is a disruption in connectivity in the default mode network DMN; Mayer et al.
The hypothesis of this study was that those participants who report persistent PCS after mTBI would have greater cognitive deficit than participants who report no long-term symptoms after mTBI. Therefore, the data was investigated to see whether increased PCS symptoms would correlate with worse cognitive performance. In addition, as PCS symptom report is influenced by other factors, such as depression, anxiety, fatigue, and post-traumatic stress, it was considered important to explore whether these co-variables correlated with cognitive performance. There was no significant correlation between performance and PCS symptom report for either task.
Although these findings do not lend definitive support for a link between PCS symptoms and cognitive performance, the overall pattern of the results suggests PCS symptoms in mTBI participants may have stronger link to cognitive performance compared to control participants. When reporting PCS symptoms using the RPQ, participants with mTBI are attributing the symptoms to the injury, whereas control subjects are not asked to make a specific attribution Dean et al.
It is therefore possible that an attribution bias is influencing the results, with a greater level of concern over the chronic cognitive effects of the injury causing participants with mTBI and persistent PCS to perform worse on the tasks. An attribution bias of this sort is likely to influence performance for all the cognitive tasks, as well as report of everyday cognitive failures CFQ score.
An attribution bias may still be influencing the results to some extent, but not enough to explain the substantial differences seen in the working memory and information processing tasks whilst the sustained attention task 0-Back is performed almost faultlessly. The influence of an attribution bias may be investigated further in follow-up studies being analyzed which use functional neuroimaging to look at underlying neural activity during this task. This indicates that the poor sleep quality of some mTBI participants may be having an effect on aspects of their daytime functioning, even if there is no difference in reported daytime sleepiness and sleep propensity.
Anecdotal evidence suggests that participants may revert to responding to all stimuli as non-targets when they felt under time pressure. Previous studies have investigated the role of sleep in the short and long-term after mTBI Ayalon et al. Registreer nu! U ontvangt een bericht als er een verandering wordt geconstateerd. Uitgebreid zoeken. Afbeelding: Alleen tonen met afbeelding. Van: Afgelopen 7 dagen. Zoeken Meer opties Reset filters. Niet gevonden wat u zocht? Sla laatste zoekopdracht op. Alle rechten voorbehouden.
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