Global Intellectual Ability Research Articles

The assessment and diagnosis of intellectual disability when development is atypical. A Norwegian population study of individuals with CHARGE syndrome

Aim This paper aimed to answer how psychometric methods based on neurotypical populations can serve as valid instruments in the assessment and diagnosis of intellectual disability in individuals with atypical development. The genetic, structural, and functional features of CHARGE make it uniquely suited to address this question. Method A Norwegian population of individuals with CHARGE (N = 35) underwent assessment procedures according to DSM-5 guidelines for the evaluation of an intellectual disability diagnosis. Results from cognitive testing (Wechsler Intelligence Scales) and parental evaluation of adaptive skills (Vineland Adaptive Behavioral Scale) were obtained and compared to their respective norm samples to explore any methodological inconsistencies. Result Significant differences emerged between the participants and the norm samples. Global cognition obtained from Wechsler revealed a bimodal distribution, suggesting a two-group sample, with the youngest children forming their own subgroup. Comparisons of the different age-groups’ performances demonstrated the lowest results among the preschoolers while the adults scored the highest. The global adaptive behavior score turned out significantly lower than the performance-based scores, thereby deflating the overall estimate of global intellectual abilities. Conclusion For individuals with CHARGE, the effect of the atypicality seemed most apparent during early childhood, stabilizing and subsiding towards adulthood. The test results’ interpretability was weakest for the preschoolers progressively increasing until peaking in adulthood, emphasizing the importance of delaying the assessment and diagnosis of intellectual disability. Because of several validity issues connected to the observation-based measure, complementary testing should precede clinical evaluations when possible in the diagnostics of individuals with CHARGE.

Global intellectual ability and adaptive functioning in children with FASD with and without sentinel facial features

ABSTRACT Background: Fetal Alcohol Spectrum Disorder (FASD) is a neurodevelopmental disorder characterized by cognitive and adaptive impairment. FASF can be presented or not with sentinel facial features (SFF). The presence of such SFF have been positively correlated with cognitive impairment in children with FASD. Objectives: The current study explores difference in global intellectual functioning and how cognition affects adaptive behavior in children with and without SFF. Methods: A total of 88 children and adolescents (55 males, 33 females) with confirmed FASD diagnosis were included in the study, of which 16 had sentinel facial features. Childrens’ neuropsychological functioning was assessed using the Wechsler Intelligence Scale for Children (WISC-V) and The Behavioral Assessment of the Dysexecutive Syndromes for Children (BADS-C). Adaptive behavior was explored through the Adaptive Behavior Assessment System (ABAS-3). Results: Children with SFF performed more poorly in tasks assessing processing speed (t = 2.495, t = .020) and executive functioning (t = 4.147, t = .001). Those children also had lower IQ scores than children without SFF (t = 2.658, t = .016). BADS-C overall scaled score was related to three of the four domains of the ABAS scale (conceptual, social, and practical) but only in the group of FASD children without SFF (B = 0.547, t = .020; B = 0.544,t = .049; B = 0.431,t = .040, respectively). Conclusions: The present study founds poorer cognitive outcomes in children who have FASD with sentinel facial features. In children without SFF, stronger executive functioning is also related to significantly stronger reported conceptual, social, and practical adaptive behaviors. Better understanding of cognitive and adaptive functioning in children with FASD may help in the design of tailored evidenced-based interventions.

The effects of sleep disordered breathing on sleep spindle activity in children and the relationship with sleep, behavior and neurocognition

Study objectivesObstructive sleep disordered breathing (SDB), has adverse neurocognitive and behavioral sequelae in children, despite conventional measures of sleep disruption being unaffected. There is growing evidence that sleep spindles may serve as a more sensitive marker of sleep quality. We investigated the relationship between sleep spindles and sleep fragmentation and neurocognition across the spectrum of SDB severity in children. MethodsChildren 3–12 years old referred for clinical assessment of SDB and age matched control children from the community were recruited and underwent polysomnography. Sleep spindles were identified manually during N2 and N3 sleep. Spindle activity was characterised as spindle number, density (number of spindles/h) and intensity (spindle density x average spindle duration). Children completed a battery of tests assessing global intellectual ability, language, attention, visuospatial ability, sensorimotor skills, adaptive behaviors and skills and problem behaviors and emotional difficulties. ResultsChildren were grouped into control, Primary Snoring, Mild OSA and Moderate/severe OSA, N = 10/group. All measures of spindle activity were lower in the SDB groups compared to the Control children and this reached statistical significance for Mild OSA (p < 0.05 for all). Higher spindle indices were associated with better performance on executive function and visual ability assessments but poorer performance on auditory attention and communication skills. Higher spindle indices were associated with better behavior. ConclusionThe reduced spindle activity observed in the children with SDB, particularly Mild OSA, indicates that sleep micro-architecture is disrupted and that this disruption may underpin the negative effects of SDB on attention, learning and memory.

O069 The effects of sleep disordered breathing on sleep spindle activity in children and the relationship with neurocognition

Abstract Introduction Conventional sleep macro-architecture measures of sleep disruption have not been associated with the adverse neurocognitive sequelae of sleep disordered breathing (SDB). Sleep spindles protecting the sleeping brain from external sensory stimuli and can serve as markers of sleep integrity. We investigated the relationship between sleep spindles and sleep fragmentation and neurocognition across the spectrum of SDB in children. Methods Children 3-12y referred for clinical assessment of SDB and age matched control children from the community were recruited. Sleep spindles were identified manually during N2 and N3 sleep. Spindle activity was characterised as spindle number, spindle density (number of spindles/ h) and spindle intensity (spindle density x average spindle duration). The Stanford-Binet Intelligence Scales measured global intellectual ability and the NeuroPSYchological assessment (NEPSY-II) measured language, attention, visuospatial ability and sensorimotor skills. Results Children were grouped into control, Primary Snoring, Mild OSA and Moderate/severe OSA, N=10/ group. All measures of spindle activity were lower in the SDB groups compared to the Control children and this reached statistical significance for Mild OSA (p&amp;lt;0.05 for all). Spindle activity was not correlated with any measure of the Stanford-Binet. Overall, all measures of spindle activity were positively correlated with the Design Copy and the Inhibition Naming combined scale score and negatively correlated with Auditory Attention subscales of the NEPSY-II. Conclusion The reduced spindle activity observed in the children with SDB, particularly Mild OSA, indicates that sleep micro-architecture is disrupted and that this disruption may underpin the negative effects of SDB on attention, learning and memory.

The Relationships Between Ataxia and Cognition in Spinocerebellar Ataxia Type 2.

The clinical spectrum of spinocerebellar ataxia type 2 includes motor manifestations and cognitive disturbances in executive functions, memory, and visuoconstructive skills. The relationships between severity of motor disturbances and altered cognition are poorly known. In this study, we assessed patients with spinocerebellar ataxia type 2 and age- and sex-matched healthy control subjects by a test battery including the Mini-mental State Examination, the Wisconsin Card Sorting test, and the Wechsler Memory Scale-Revised. The correlation between severity of motor ataxia (as assessed by a validated and widely used severity scale, the SARA scale, and by an objective automated computerized system of gait analysis) and altered cognition was then evaluated by Spearman correlation analysis. Patients performed worse than healthy controls in almost all administered neuropsychological tests. Nevertheless, only global intellectual abilities and executive functions significantly correlated with the overall severity of ataxia as assessed by the SARA scale, and impaired executive functions alone correlated with performance on several spatio-temporal gait analysis parameters. Our findings would probably suggest a prominent influence of executive functions on motor abilities in patients with spinocerebellar ataxia type 2 and raise the possibility that cognitive pharmaceutical or rehabilitative interventions may be of benefit in the management of motor problems in these patients.

Gender differences in academic achievement: The mediating role of personality

Research has shown pervasive gender differences in academic achievement. Because both genders present similar global intellectual ability levels, interest has arisen concerning the role of non-intellectual factors in explaining these differences. In this study, the mediating role of personality dimensions related to disconstraint and aggressiveness, in the relationship between gender and academic achievement is assessed. The sample consists of 351 adolescents, ranging in age from 14 to 18years old. The instruments are the aggressiveness and disconstraint PSY-5 dimensions of the MMPI-A and the School Life Survey (SLS). MANOVA shows that females report better indicators of achievement, the frequency of behavioral problems and overall satisfaction. Regression analyses using bootstrapping procedures reveal the full mediation effects of disconstraint, but not of aggressiveness, on the influence of gender on achievement. The results are discussed in light of the role of disconstraint-related personality characteristics for academic success and the potential factors underlying gender variability in these characteristics.

Cognitive Trajectories in 4 Patients With Pediatric-Onset Multiple Sclerosis

Cognitive dysfunction is common in pediatric-onset multiple sclerosis, but long-term data on cognitive maturation in these patients are sparse. We report the clinical features and cognitive trajectories in 4 pediatric-onset multiple sclerosis patients who were 10 years or younger at first attack and were followed between 1998 and 2010. Relapses in all 4 patients were frequent early in the disease and became infrequent or absent over time. Declines on neuropsychological testing were most pronounced on measures of processing speed, specifically visuomotor speed, and executive control requiring mental sequencing and set shifting, whereas global intellectual ability and phonemic fluency remained stable or improved over time. These case studies demonstrate a negative impact of multiple sclerosis on cognitive development in the long term and suggest that continued observation into adulthood is required to appreciate the vocational consequences of pediatric-onset multiple sclerosis.

Determinants of adult functional outcome in adolescents receiving special educational assistance

This study investigates the role of IQ, autistic traits and challenging behaviours in affecting adult outcomes among adolescents who receive special educational assistance. A total of 58 participants were recruited from an ongoing longitudinal study. All received assessments of IQ, behavioural patterns (using the Childhood Behaviour Checklist - CBCL) and autistic traits (using the Social Communication Questionnaire - SCQ) during adolescence and were followed up 6 years later (at a mean age of 22 years) using the World Health Organization Disability Assessment Schedule II (WHO-DAS II) to assess functional outcome. A significant positive relationship was found between CBCL score and WHO-DAS II score (β = 0.511, P = 0.001). IQ score showed a negative relationship with total WHO-DAS II score (β = -0.247, P = 0.04). SCQ score was not found to significantly influence total WHO-DAS II score (β = -0.028, P = 0.84). Although the role of global intellectual ability is important, these results stress the highly predictive value of adolescent behaviours on functional outcomes in adult life among young adults receiving special educational assistance.

Neuropsychological Profile of Italian Children and Adolescents with 22q11.2 Deletion Syndrome with and Without Intellectual Disability

As individuals with chromosome 22q11.2 deletion syndrome (22q11DS) show a wide range of IQs, intellectual heterogeneity could mask the neuropsychological profile of the syndrome. This study was designed to identify specific neuropsychological features of children and adolescents with 22q11DS by taking into account the possible source of variability deriving from intellectual disability (ID). First, we compared several neuropsychological domains involving linguistic, visual-motor/visual-perceptual and memory abilities in 34 children and adolescents with 22q11DS and 83 mental age-matched typically developing (TD) participants. Then, we selected participants with 22q11DS according to whether or not they had ID and compared their neuropsychological profiles with those of chronological age-matched TD controls. Although language and several aspects of memory have been found impaired only in children with 22q11DS with ID, deficits in visual-spatial abilities and visual-object short-term memory persist in participants without ID and might be considered a characteristic of 22q11DS, not just related to the presence of ID. On the basis of our findings, children and adolescents with 22q11DS cannot be considered as a single group with a homogeneous neuropsychological profile and must be studied in relation to their global intellectual abilities.

Extreme prematurity and neuropsychological outcome in the preschool years

With the increasing survival of extremely preterm (EP) birth infants in the surfactant era, the longer-term outcome of infants born at the threshold of viability has become a vital topic of study. The goal of this investigation was twofold. First, while taking into account the influence of sociodemographic confounds, we wished to investigate neuropsychological outcome differences between two groups of EP preschoolers: 23-24 weeks (n = 20), and 25-26 weeks' (n = 21) gestation at delivery. Second, we wished to explore whether, within the population of EP preschoolers, gestational maturity accounts for a unique portion of the variance in neuropsychological outcome, over and above the variance explained by ante-, peri-, and neonatal complications, or treatment factors. The findings revealed group differences, ranging from .70 to .80 of a standard deviation in general intellectual abilities, nonverbal intelligence, and global motor performance, in favor of the more mature EP group. Additionally, gestational maturity was found to explain a unique portion of the variance in global intellectual and motor abilities. These findings are interpreted from the perspective that gestational age is an index of the vulnerability of the central nervous system to disruption of developmentally regulated processes.

Speech and school performance in children with benign partial epilepsy with centro-temporal spikes (BCECTS)

Purpose To assess prospectively language and speech ability in children with benign partial epilepsy with centro-temporal spikes (BCECTS). To evaluate academic performance and social competencies both during the active disease and after remission. Methods Right-handed school children with typical BCECTS and a control group matched by age, sex, handedness and socioeconomic status were examined. The German version of WISC-R, the “Tübinger Luria Christensen Neuropsychological Test Set for children” (TÜKI), the “Verbal Learning Memory Test” (VLMT), the “Heidelberger Speech Development Test-second edition” (HSET), and the “Salzburger reading and writing test” (SLRT) were applied. The Child Behavior Checklist (CBCL) and a semi-structured interview were performed with the children's teachers to gain insight into school performance, behavioral and emotional problems. Results During the active phase, the patient group – despite normal global intellectual abilities – showed few, but significant impairments both in expressive speech and in receptive and expressive vocabulary. A significant deficit in the ability to recognize and express interpersonal relations was also found. Patients’ teachers stated deficits concerning academic performance and complained about disturbing behavior. Parents reported significantly more psycho-pathological features in the subscales “Aggressive Behavior”, “Attention Problems” and “Anxious/Depressed” of the CBCL. Results were independent of medication and spike localization. After complete recovery from BCECTS, these problems were not found any more. Conclusions Both deficits of speech-related abilities (in both expressive and receptive vocabulary) and behavioral disturbances can be detected in children with typical BCECTS, but are no longer apparent after remission of the seizure disorder.

Neuropsychological attention deficits in tuberous sclerosis complex (TSC)

Tuberous sclerosis complex (TSC) (OMIM191100) is a genetic disorder with multi-system involvement including neurodevelopmental manifestations. There is great interest in understanding the pathogenetic mechanisms underlying these neurobehavioral and neurocognitive manifestations. However, there are still significant gaps in knowledge about the exact neuropsychiatric phenotypes observed in TSC. Here we report on the first systematic evaluation of neuropsychological attentional skills in a population-derived sample of children and adolescents with TSC. The study showed that, even when age, gender, IQ, and intra-familial clustering were controlled for, the TSC group had significantly lower scores than their unaffected siblings on a range of neuropsychological attentional tasks, and that they had significantly more neuropsychological attention deficits. Eighteen of the 20 children (90%) showed deficits on one or more attentional tasks, with dual task performance most consistently impaired (85%) and visual selective attention a relative strength. Active seizures and anti-epilepsy medication did not influence attentional profiles. Furthermore, parent rating of attention-related behaviors were not able to identify children at risk of neuropsychological deficits. The findings suggest that clinical neuropsychological evaluation of attentional skills should be performed in children and adolescents with TSC even when they have normal global intellectual abilities, no seizures, and no disruptive behaviors. Results suggest that the mechanisms underlying these deficits may include contributions from structural, seizure-related and molecular factors.

Executive Functions and the Ability to Sustain Vigilance During Sleep Loss

There is considerable individual variability in the ability to sustain performance during sleep loss. Preliminary evidence suggests that individuals with higher trait-like activation/functioning of the prefrontal cortex may be less vulnerable to fatigue. We tested this hypothesis in a sample of 54 healthy volunteers who were assessed bi-hourly on a variant of the Psychomotor Vigilance Test during 41 h of sleep deprivation. A subset of these subjects, representing the top and bottom 25% of the sample based on their ability to sustain vigilance performance during sleep deprivation, were compared with respect to baseline neurocognitive abilities. The sleep deprivation Resistant group (N = 13) scored significantly higher than the sleep deprivation Vulnerable (N = 13) group on all three baseline tasks assessing prefrontal executive function abilities (letter fluency, Stroop Color-Word test, Color Trails Form 2), whereas no differences were found on non-executive function tasks. Similarly, groups showed no differences on demographic variables including age, education, hand preference, morningness-eveningness preference, global intellectual ability, or pre-study sleep history. Findings are consistent with the hypothesis that greater prefrontal/executive functioning may be protective against the adverse effects of sleep deprivation and suggest that baseline executive function testing may prove useful for prediction of resilience during sleep loss.

Overlapping numerical cognition impairments in children with chromosome 22q11.2 deletion or Turner syndromes

Children with one of two genetic disorders (chromosome 22q11.2 deletion syndrome and Turner syndrome) as well typically developing controls, participated in three cognitive processing experiments. Two experiments were designed to test cognitive processes involved in basic aspects numerical cognition. The third was a test of simple manual motor reaction time. Despite significant differences in global intellectual abilities, as measured by IQ tests, performance on the two numerical cognition tasks differed little between the two groups of children with genetic disorders. However, both performed significantly more poorly than did controls. The pattern of results are consistent with the hypothesis that impairments were not due to global intellectual ability but arose in specific cognitive functions required by different conditions within the tasks. The fact that no group differences were found in the reaction time task, despite significant differences in the standardized processing speed measure, further supports the interpretation that specific cognitive processing impairments and not global intellectual or processing speed impairments explain the pattern of results. The similarity in performance on these tasks of children with unrelated genetic disorders counters the view that numerical cognition is under any direct genetic control. Instead, our findings are consistent with the view that disturbances in foundational spatiotemporal cognitive functions contribute to the development of atypical representations and processes in the domains of basic magnitude comparison and simple numerical enumeration.

A New Measure of Visual Location Learning and Memory: Development and Psychometric Properties for the Brown Location Test (BLT)

There are a variety of well-established neuropsychological tests that are helpful in identifying global and specific verbal memory deficits. In contrast, tests of visual memory have produced less consistent results likely due in part to confounding variables such as verbal encodability, administration difficulties, and insufficient differentiation of among types of visual memory. The Brown Location Test (BLT) was designed to specifically measure visual memory for location of identical objects (dots) and address limitations found in commonly employed visual memory tests. This paper describes the empirical basis for the BLT and reports the psychometric properties of the test. Results indicate good internal and alternate form reliabilities. Factor analysis of a brief test battery confirmed that BLT performance is generally independent of verbal memory and global intellectual abilities. BLT performance declined with age, but there was no association between performance and gender, education, or intellectual functioning. In view of the favorable psychometric properties observed during preliminary studies, additional normative and validation studies in healthy and patient populations are warranted.

Cognitive Functions in Juvenile and Adult Patients with Gelastic Epilepsy due to Hypothalamic Hamartoma

To describe extend and severity of cognitive deficits in juvenile and adult patients with gelastic seizures and hypothalamic hamartoma (HH) and to analyze the impact of epilepsy-related variables on cognitive performance. Thirteen juvenile and adult patients (mean age, 25 years; seven men) underwent comprehensive neuropsychological testing assessing intellectual performance, attention and executive functions, verbal and visual memory, and visuospatial abilities. Intellectual abilities ranged from moderate mental retardation to good average performance; 54% of the patients displayed below-average global intellectual abilities. Attentional and executive functions were impaired in 23% to 46% of the patients. Below-average visuospatial capabilities were observed in 39% of the cases. Memory functions were impaired regarding both visual (77%) and verbal learning (62%). Nonparametric correlation analysis revealed a significant relation between monthly partial seizure frequency and reduced cognitive flexibility and reduced performance in mental rotation. In addition, HH volume was significantly negatively correlated with cognitive flexibility, whereas age at onset and duration of epilepsy did not show significant correlation to cognitive performance. More than half of the adult patients with gelastic seizures and HH displayed deficits in a broad range of cognitive functions, expressed mostly in visual and verbal learning and memory. Some of the deficits could be shown to correlate with disease-related characteristics representing the severity of the epilepsy or the size of the underlying lesion. These findings prompt for a longitudinal investigation of the development of these cognitive deficits to analyze further the relevant factors contributing to this wide spectrum of cognitive impairments.

Functional Plasticity or Vulnerability After Early Brain Injury?

Traumatic brain injury (TBI) is a common, acquired, childhood disability that may be used as a model to understand more completely the impact of early brain injury on both brain structure and day-to-day function. Contrary to previously held views of the "plasticity" of the young brain, recent research suggests that such early insults may have a profound impact on development. To date, these suggestions remain largely untested. To plot changes in cognitive abilities after childhood TBI over the 30 months after injury and to examine the impact of age at injury on cognitive outcomes. Prospective longitudinal study. Royal Children's Hospital, Victoria, Australia. Global intellectual ability, verbal and nonverbal skills, attention, and processing speed. A total of 122 children admitted to the hospital with a diagnosis of TBI were divided according to injury age, ie, young (age: 3-7 years) or old (age: 8-12 years), and injury severity (mild, moderate, or severe) and were evaluated acutely and at 12 and 30 months after injury. An additional sample of children injured before 3 years of age (n = 27) was compared with these groups with respect to global intellectual ability only. A clear relationship was documented between injury severity and cognitive performance. For children who sustained severe injury, younger age at injury was associated with minimal, if any, recovery after injury, but better outcomes were observed after severe TBI among older children. Age at injury was not predictive of outcomes for children with mild or moderate TBI, although infants (age: 0-2.11 years) with moderate TBI showed poorer outcomes than did older children with injury of similar severity. Findings support a "double-hazard" model for severe and early brain insults and add to the ongoing debate regarding cerebral plasticity, suggesting that, contrary to traditional views, young children who sustain severe TBI in early childhood or moderate or severe TBI in infancy may be particularly vulnerable to significant residual cognitive impairment. From a clinical perspective, results indicate that long-term follow-up monitoring and management should be targeted to this high-risk group.

Behavioral and Cognitive Aspects of Tuberous Sclerosis Complex

Tuberous sclerosis complex is a multisystem genetic disorder. Of all the possible manifestations of this complex disorder, the cognitive and behavioral problems represent the area of greatest concern to parents and caregivers. This review outlines the current evidence regarding global intellectual abilities, behavioral problems, psychiatric diagnoses, learning disorders, and specific neuropsychologic deficits for which individuals with tuberous sclerosis complex are at particularly increased risk, and outlines approaches to intervention. Approximately half of individuals diagnosed with tuberous sclerosis complex present with global intellectual impairment and developmental psychopathologies. Those with normal intellectual abilities are also at high risk of specific neuropsychologic deficits and behavioral, learning, and other psychiatric disorders. There is no evidence for an inevitable decline in cognition or behavior, and any such changes should be investigated. The evolving neurocognitive literature suggests that frontal brain systems might be most consistently disrupted by tuberous sclerosis complex-related neuropathology, thus leading to abnormalities in regulatory and goal-directed behaviors.

The effects of multiple shunt revisions on neuropsychological functioning and memory

The focus of this study was to determine the effect of multiple shunt revisions on cognition and memory. The present study attempted to document a discrepancy in the functioning of children with hydrocephalus having numerous shunt revisions compared to those with only an initial shunt surgery. Researchers have found an increasing number of children with hydrocephalus requiring shunt revisions. In the current literature there are many conflicting views regarding the effects of hydrocephalus on cognition and memory. Many researchers report that properly treated hydrocephalus will not have a negative impact on cognitive functioning. Furthermore, researchers found that factors such as the total number of shunt revisions do not negatively impact global intellectual ability. Forty-six subjects between the ages of six and 16 years participated in the study. The subjects were recruited from the Department of Neurosurgery at an urban pediatric hospital. Specific inclusion and exclusion criteria were met. Independent variables for the study included shunt revisions; seizures, and Attention Deficit Hyperactivity Disorder (ADHD). Subject groupings were based on whether the subjects required multiple shunt revisions or single shunt placement and the presence or absence of seizures and ADHD. Dependent variables included the subject’s performance on measures of cognition and memory. Measures of functioning included the Wechsler Intelligence Scale for Children-Third Edition and the Wide Range Assessment of Learning and Memory- Screener. The results of this study did not support the presence of cognitive or memory impairments as a result of multiple shunt revisions. Anecdotal findings noted that seizures were the only independent variable to significantly account for the observed variance in scores of cognition, specifically Full Scale IQ, Verbal Comprehension, and Perceptual Organization. [Neurol Res 2000; 22: 131-136]

Category specific semantic loss in dementia of Alzheimer's type. Functional-anatomical correlations from cross-sectional analyses.

In the context of focal brain injury, selective loss of semantic knowledge in the domain of either natural kinds or artefacts is usually considered to reflect the differential importance of temporal and frontoparietal regions to the representations of perceptual and functional attributes, respectively. It is harder to account far as a feature of a more diffuse process, and previous cross-sectional analyses of patients with dementia of Alzheimer's type (DAT) have differed over whether category effects occur. In our series of 58 patients with probable DAT, we demonstrated a significant group advantage for artefacts, and explored possible reasons for the inconsistency of this finding in other studies. A multiple single-case strategy revealed not only individuals with consistent advantages for artefacts but also individuals with consistent advantages for natural kinds. By ranking the individuals according to measures of naming performance and global intellectual ability, we showed that the strength of the group advantage for artefacts was dependent on the former but not the latter variable. The findings are discussed in the context of two competing theories of semantic breakdown in DAT. One differentiates between domains of knowledge in terms of the structure of semantic representations within a single distributed network; the other emphasizes the importance of different brain regions in the category distinction. We conclude that our findings are in keeping with the predictions of the latter hypothesis.