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The utility of injury characteristics for predicting the severity of post-concussion outcomes remains equivocal. The purpose of this meta-analysis was to quantify the predictive relationship between these variables to inform classification of acute injury severity. Thirty-one empirical samples of concussed athletes, for which rates of loss of consciousness and/or amnesia were reported, were included in a meta-analysis evaluating acute outcomes following sports-related concussion. Outcome measures of interest were neuropsychological tests first administered 1–10 days post-injury. Loss of consciousness and anterograde amnesia significantly predicted more severe neuropsychological deficits within 10 days of concussion in studies using pre-injury baseline, but not control group, comparisons. Retrograde amnesia significantly predicted acute neuropsychological dysfunction (d = -1.03) irrespective of comparison group. Although small sample sizes require conservative interpretation and future replication, the evidence suggests that retrograde amnesia, rather than loss of consciousness, may be used to classify the acute severity of concussion. (JINS, 2014, 20, 81–87)
The objective of this study is to determine which pre-existing athlete characteristics, if any, are associated with greater deficits in functioning following sports-related concussion, after controlling for factors previously shown to moderate this effect (e.g., time since injury). Ninety-one independent samples of concussion were included in a fixed+systematic effects meta-analysis (n = 3,801 concussed athletes; 5,631 controls). Moderating variables were assessed using analogue-to-ANOVA and meta-regression analyses. Post-injury assessments first conducted 1–10 days following sports-related concussion revealed significant neuropsychological dysfunction, postural instability and post-concussion symptom reporting (d = −0.54, −1.10, and −1.14, respectively). During this interval, females (d = −0.87), adolescent athletes competing in high school competitions (d = −0.60), and those with 10 years of education (d = −1.32) demonstrated larger post-concussion neuropsychological deficits than males (d = −0.42), adults (d = −0.25), athletes competing at other levels of competition (d = −0.43 to −0.41), or those with 16 years of education (d = −0.15), respectively. However, these sub-groups’ differential impairment/recovery beyond 10 days could not be reliably quantified from available literature. Pre-existing athlete characteristics, particularly age, sex and education, were demonstrated to be significant modifiers of neuropsychological outcomes within 10 days of a sports-related concussion. Implications for return-to-play decision-making and future research directions are discussed. (JINS, 2013, 19, 1–17).
Schizophrenia has been identified as a disorder of the frontostriatal system with impairments in both sustained and selective attention (Bradshaw, 2001). The Sustained Attention to Response Task (SART), which required occasional withholding of an ongoing frequent response when a specified digit occurred, was completed by patients with a clinical diagnosis of schizophrenia (N = 52) and matched controls (N = 46). Relative to controls, participants with schizophrenia responded less frequently and made more impulsive errors. Their correct responses were slower on average, with greater variability in timing. Speed of response was unrelated to neuroleptic medication dosage. The slow responses exhibited by patients with schizophrenia were interpreted as reflecting primarily motor frontostriatal circuit dysfunction, and dysfunction of the lateral orbitofrontal/anterior cingulate circuit is implicated in poor impulse control. To address the heterogeneity of symptoms in schizophrenia, symptom dimension scores (positive, negative and disorganised) were used to determine whether symptom dimensions were associated with differential performance on the SART. Higher negative symptoms were related to increased miss errors on the SART whereas higher disorganised and positive symptom scores were unrelated to performance on this measure. An association between negative symptoms and increased miss errors may be considered indicative of dysfunction of the anterior cingulate circuit, considered to be linked to response inattention, apathy, reduced initiative and focused attention. Implications of this research for understanding the neuroanatomical basis for schizophrenia and its subtypes are discussed.
Amultidisciplinary collaborative study examining cognition in a large sample of twins is outlined. A common experimental protocol and design is used in The Netherlands, Australia and Japan to measure cognitive ability using traditional IQ measures (i.e., psychometric IQ), processing speed (e.g., reaction time [RT] and inspection time [IT]), and working memory (e.g., spatial span, delayed response [DR] performance). The main aim is to investigate the genetic covariation among these cognitive phenotypes in order to use the correlated biological markers in future linkage and association analyses to detect quantitativetrait loci (QTLs). We outline the study and methodology, and report results from our preliminary analyses that examines the heritability of processing speed and working memory indices, and their phenotypic correlation with IQ. Heritability of Full Scale IQ was 87% in the Netherlands, 83% in Australia, and 71% in Japan. Heritability estimates for processing speed and working memory indices ranged from 33–64%. Associations of IQ with RT and IT (−0.28 to −0.36) replicated previous findings with those of higher cognitive ability showing faster speed of processing. Similarly, significant correlations were indicated between IQ and the spatial span working memory task (storage [0.31], executive processing [0.37]) and the DR working memory task (0.25), with those of higher cognitive ability showing better memory performance. These analyses establish the heritability of the processing speed and working memory measures to be used in our collaborative twin study of cognition, and support the findings that individual differences in processing speed and working memory may underlie individual differences in psychometric IQ.
Genetic and environmental sources of covariation among cognitive measures of verbal IQ, performance IQ (PIQ), academic achievement, 2-choice reaction time (CRT), inspection time (IT) and the 6 Openness facets of the NEO Personality Inventory-Revised (NEO PI-R) were examined. The number of twin and twin–sibling pairs ranged from 432 (182 MZ, 350 DZ/sibling) to 1023 (273 MZ, 750 DZ/sibling) for cognitive measures, and between 432 (90 MZ, 342 DZ/sibling) — 437 (91 MZ, 346 DZ/sibling) for Openness facets. Structural equation modeling best supported a model with a 3-factor additive genetic structure. A genetic general factor subsumed the 5 cognitive measures and 5 of the 6 Openness facets (Actions did not load significantly). A second additive genetic factor incorporated the 6 Openness facets, and a third additive genetic factor incorporated the 5 cognitive measures. Specific additive and dominance genetic effects were also evident, as were shared common and shared unique environmental influences, and specific unique environmental effects. The Openness facets of Ideas and Values evidenced the strongest phenotypic correlations with cognitive indices, particularly verbal measures. The genetic correlations among Openness facets and cognitive measures ranged from −.06 to .79. Results were interpreted as suggesting that Openness is related to general cognitive ability (g) through a genetic mechanism and that gengenders a minor but discernable disposition towards Openness for the majority of facets.
Simultaneous analysis of handedness data from 35 samples of twins (with a combined sample size of 21,127 twin pairs) found a small but significant additive genetic effect accounting for 25.47% of the variance (95% confidence interval [CI] 15.69–29.51%). No common environmental influences were detected (C = 0.00; 95% CI 0.00–7.67%), with the majority of the variance, 74.53%, explained by factors unique to the individual (95% CI 70.49–78.67%). No significant heterogeneity was observed within studies that used similar methods to assess handedness, or across studies that used different methods. At an individual level the majority of studies had insufficient power to reject a purely unique environmental model due to insufficient power to detect familial aggregation. This lack of power is seldom mentioned within studies, and has contributed to the misconception that twin studies of handedness are not informative.
The assessment of executive functioning 1 month following a mild traumatic brain injury (MTBI) is minimal, inconsistent and difficult to integrate. Four executive processes of checking, inhibition, sharing and integrating were examined using an empirically derived assessment protocol based on executive process delineation (Baddeley & Della Sala, 1998). This protocol was administered to individuals at 1 month post-MTBI (n = 22), and a group of orthopaedic controls (n = 15) matched for age, sex, years of education and occupational status. Contrary to expectations, only one significant difference between the two groups occurred on the dual-task Telephone Search while Counting (p < .006), which was considered a measure of the executive process of sharing. Methodological limitations such as a small and heterogeneous sample may have influenced the findings in this study. The results provide support for the utility of a theoretically driven approach to executive functioning to aid the integration of neuropsychological results, and highlight the need for carefully controlled research at 1 month following a MTBI to further delineate the recovery process.
The present study aimed to determine whether including a sensitive test of immediate and delayed recall would improve the diagnostic validity of the Rapid Screen of Concussion (RSC) in mild Traumatic Brain Injury (mTBI) versus orthopaedic clinical samples. Two studies were undertaken. In Study 1, the performance of 156 mTBI and 145 orthopaedic participants was analysed to identify the number of individuals who performed at ceiling on the verbal memory subtest of the RSC, as this test required immediate and delayed recall of only five words. A second aim was to determine the sensitivity and specificity levels of the RSC. Study 2 aimed to examine whether replacement of the verbal memory subtest with the 12-word Hopkins Verbal Learning Test (HVLT) could improve the sensitivity of the RSC in a new sample of 26 mTBI and 30 orthopaedic participants. Both studies showed that orthopaedic participants outperformed mTBI participants on each of the selected measures. Study 1 showed that 14% of mTBI participants performed at ceiling on the immediate and 21.2% on delayed recall test. Performance on the original battery yielded a sensitivity of 82%, specificity of 80% and overall correct classification of 81.5% participants. In Study 2, inclusion of the HVLT improved sensitivity to a level of 88.5%, decreased specificity to a level of 70% and resulted in an overall classification rate of 80%. It was concluded that although inclusion of the five-word subtest in the RSC can successfully distinguish concussed from non-concussed individuals, use of the HVLT in this protocol yields a more sensitive measure of subtle cognitive deficits following mTBI.
Although the n-back task has been widely applied to neuroimagery investigations of working memory (WM), the role of practice effects on behavioural performance of this task has not yet been investigated. The current study aimed to investigate the effects of task complexity and familiarity on the n-back task. Seventy-seven participants (39 male, 38 female) completed a visuospatial n-back task four times, twice in two testing sessions separated by a week. Participants were required to remember either the first, second or third (n-back) most recent letter positions in a continuous sequence and to indicate whether the current item matched or did not match the remembered position. A control task, with no working memory requirements required participants to match to a predetermined stimulus position. In both testing sessions, reaction time (RT) and error rate increased with increasing WM load. An exponential slope for RTs in the first session indicated dual-task interference at the 3-back level. However, a linear slope in the second session indicated a reduction of dual-task interference. Attenuation of interference in the second session suggested a reduction in executive demands of the task with practice. This suggested that practice effects occur within the n-back task and need to be controlled for in future neuroimagery research using the task.
The aims were to investigate the general and specific effects of mild traumatic brain injury (mTBI), and if people with orthopaedic injuries who had sustained their injuries through exposure to acceleration/deceleration force could have sustained a brain injury. The Rapid Screen of Concussion and Digit Symbol Substitution Test were given to patients with mTBI (89 male, 23 female), and patients with orthopaedic injuries that did (27 male, 5 female) or did not (27 male, 15 female) involve deceleration forces within 24 hours of injury. A group of uninjured people (31 male, 12 female) were also tested. Compared to all other groups, patients with mTBI recalled fewer words and correctly answered fewer orientation questions. Patients with either mTBI or deceleration orthopaedic injuries showed slower speed of information processing than patients with nondeceleration orthopaedic injuries or participants without injury. Nondeceleration patients and uninjured participants did not differ. These results suggest that there are both general injury effects and specific mTBI effects on efficiency of cognitive functioning. The results also highlight the probability that patients with a diagnosis of orthopaedic injury who were exposed to acceleration/deceleration forces may have suffered a mild brain injury as well.
Dual task performance in children with Tourette Syndrome (TS) was studied. The participants were children with TS (N = 48, 40 male, 8 female), Attention Deficit Hyperactivity Disorder (ADHD; mixed types N = 44, 34 male, 10 female) and unaffected controls (N = 48, 34 male, 14 female). Eleven of the TS participants had no comorbidities (TS only) and they were compared to matched groups of participants with TS plus comorbidities (TS+), ADHD, and controls. Each participant was administered screening measures of behaviour, intelligence and verbal ability, as well as specific tests of dual task performance. Children with TS-only correctly recalled fewer digit span forward trials, and identified fewer spaceship pairs than controls under single task conditions in the SkySearch subtest of the Test of Everyday Attention for Children. However, the TS-only and control groups showed better counting performance while simultaneously searching for targets, than the TS+ and ADHD groups. Taken together, these results suggest that some previously reported cognitive deficits in children with TS are due to comorbidities, rather than to the syndrome itself.
This study investigated the generalisability of the Rapid Screen of Concussion (RSC; a series of brief computerised tests) and the Digit Symbol Substitution Test (DSS; Wechsler, 1981) for discriminating between concussion (mTBI) and orthopaedic patient groups in two different centres, the Royal Brisbane Hospital, Brisbane (N = 177) and St. Vincent's Hospital, Sydney (N = 211). Group differences and interactions were assessed between test centre (Sydney or Brisbane) and injury type (mTBI or orthopaedic control) on a composite variable of the RSC and DSS subtests. Age, education and number of standard drinks of alcohol consumed were covaried for these analyses. While the mTBI patients obtained lower scores than orthopaedic patients, there were no significant differences between Brisbane and Sydney participants in performance on the RSC and DSS. There was no significant interaction between injury type and test centre. Similarities of correct classification rates of the RSC and DSS for Brisbane and Sydney were examined using a double cross-validation technique. When cross-validating from the Brisbane to Sydney sample it was revealed that sensitivity was 73% in Brisbane and 71% in Sydney, while specificity for the two samples was 76% and 67%, respectively. When cross-validating from the Sydney sample to the Brisbane sample sensitivity was 64% and 63%, respectively. Specificity was 81% in Sydney and 80% in Brisbane. These results indicated that correct classification rates were sufficiently similar between the cities and that the RSC and DSS could be generalised. When samples were combined, sensitivity was found to be 66% while specificity was 80%. The RSC and DSS are recommended as adjunct procedures to medical diagnoses of mTBI.
The application of neuroscience advances to brain injury is addressed in the context of our studies of the role of the corpus callosum in the interhemispheric transfer of auditory and tactile information. The outcome of these studies, which were conducted over a period of 30 years in normal individuals as well as those with congenital and acquired lesions of the corpus callosum, have since been confirmed and extended by modern brain imaging techniques. These techniques nevertheless continue to rely on the use of sensitive, specific, valid and reliable behavioural testing paradigms.
This study examined the genetic and environmental relationships among 5 academic achievement skills of a standardized test of academic achievement, the Queensland Core Skills Test (QCST; Queensland Studies Authority, 2003a). QCST participants included 182 monozygotic pairs and 208 dizygotic pairs (mean 17 years ± 0.4 standard deviation). IQ data were included in the analysis to correct for ascertainment bias. A genetic general factor explained virtually all genetic variance in the component academic skills scores, and accounted for 32% to 73% of their phenotypic variances. It also explained 56% and 42% of variation in Verbal IQ and Performance IQ respectively, suggesting that this factor is genetic g. Modest specific genetic effects were evident for achievement in mathematical problem solving and written expression. A single common factor adequately explained common environmental effects, which were also modest, and possibly due to assortative mating. The results suggest that general academic ability, derived from genetic influences and to a lesser extent common environmental influences, is the primary source of variation in component skills of the QCST.
It has been suggested that twinning may influence handedness through the effects of birth order, intra-uterine crowding and mirror imaging. The influence of these effects on handedness (for writing and throwing) was examined in 3657 Monozygotic (MZ) and 3762 Dizygotic (DZ) twin pairs (born 1893–1992). Maximum likelihood analyses revealed no effects of birth order on the incidence of left-handedness. Twins were no more likely to be left-handed than their singleton siblings (n = 1757), and there were no differences between the DZ co-twin and siblingtwin covariances, suggesting that neither intra-uterine crowding nor the experience of being a twin affects handedness. There was no evidence of mirror imaging; the co-twin correlations of monochorionic and dichorionic MZ twins did not differ. Univariate genetic analyses revealed common environmental factors to be the most parsimonious explanation of familial aggregation for the writing-hand measure, while additive genetic influences provided a better interpretation of the throwing hand data.
The n-back task was hypothesized to be a dual task,
permitting the imposition of parametrically increasing attentional
and working memory demands, while keeping constant the demands
of an embedded matching subtask. Visual targets were presented
for 200 ms every 2.2 s at pseudorandomly varying positions on
a computer screen. Participants were required to remember the
most recent 0, 1, 2, or 3 positions and responded with a choice
button push to whether the current target position matched the
position presented n items previously. P300 peak latency
was constant across n-back tasks, reflecting constant
perceptual and cognitive demands of the matching subtask. P300
peak amplitude decreased with increasing memory load, reflecting
reallocation of attention and processing capacity away from
the matching subtask to working memory activity. These data
support a dual-task nature of the n-back, which should
be considered when employing this paradigm.
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