Maureen Dennis

Why IQ is not a covariate in cognitive studies of neurodevelopmental disorders

IQ scores are volatile indices of global functional outcome, the final common path of an individuals genes, biology, cognition, education, and experiences. In studying neurocognitive outcomes in children with neurodevelopmental disorders, it is commonly assumed that IQ can and should be partialed out of statistical relations or used as a covariate for specific measures of cognitive outcome. We propose that it is misguided and generally unjustified to attempt to control for IQ differences by matching procedures or, more commonly, by using IQ scores as covariates. We offer logical, statistical, and methodological arguments, with examples from three neurodevelopmental disorders (spina bifida meningomyelocele, learning disabilities, and attention deficit hyperactivity disorder) that: (1) a historical reification of general intelligence, g, as a causal construct that measures aptitude and potential rather than achievement and performance has fostered the idea that IQ has special status and that in studying neurocognitive function in neurodevelopmental disorders; (2) IQ does not meet the requirements for a covariate; and (3) using IQ as a matching variable or covariate has produced overcorrected, anomalous, and counterintuitive findings about neurocognitive function.

Social Outcomes in Childhood Brain Disorder: A Heuristic Integration of Social Neuroscience and Developmental Psychology.

The authors propose a heuristic model of the social outcomes of childhood brain disorder that draws on models and methods from both the emerging field of social cognitive neuroscience and the study of social competence in developmental psychology/psychopathology. The heuristic model characterizes the relationships between social adjustment, peer interactions and relationships, social problem solving and communication, social-affective and cognitive-executive processes, and their neural substrates. The model is illustrated by research on a specific form of childhood brain disorder, traumatic brain injury. The heuristic model may promote research regarding the neural and cognitive-affective substrates of childrens social development. It also may engender more precise methods of measuring impairments and disabilities in children with brain disorder and suggest ways to promote their social adaptation.

Neuropsychological sequelae of the treatment of children with medulloblastoma

SummaryWhen a malignant tumor invades the childs cerebellum, the cost of successful treatment is often significant cognitive morbidity. A review of neuropsychological outcome revealed that survivors of childhood medulloblastoma (MB) have long-term deficits in intelligence, memory, language, attention, academic skills, psychosocial function, and a compromised quality of life. These deficits varied with chronological age at tumor diagnosis and/or adjuvant treatment, type and duration of presenting symptoms, tumor extension beyond the cerebellum, a history of adjuvant radiation treatment, and time since treatment. The effects on neuropsychological outcome of other factors, such as post-surgical hydrocephalus, were less clear. To understand the interaction between two factors predictive of outcome, age at diagnosis and time since treatment, we analyzed IQ results for a new sample of 25 surgically-treated and radiated MB survivors, and found that age at diagnosis and time since treatment made separable contributions to intellectual morbidity. PIQ appeared to measure some general effects of diffuse cerebral insult because it varied with chronological age of the child at tumor diagnosis but was relatively constant in magnitude, once established. VIQ, in contrast, was somewhat less sensitive to age at diagnosis in treated MB survivors, but declined with time since treatment. These results are important for understanding the academic attainments and continuing rehabilitation needs of childhood MB survivors, because they suggest that these children progressively fail to assimilate new verbally-based knowledge at a developmentally-appropriate rate.

Attentional–inhibitory control and social–behavioral regulation after childhood closed head injury: Do biological, developmental, and recovery variables predict outcome?

Attentional-inhibitory control and social-behavioral regulation are two outcome domains commonly impaired after childhood closed head injury (CHI). We compared neuropsychological tests of attentional-inhibitory control (vigilance, selective attention, response modulation) and social discourse and intentionality (inferencing, figurative language, and speech acts) with parent ratings of attention and behavioral regulation in relation to four injury-related variables: age at CHI, time since CHI, CHI injury severity, and frontal lobe injury moderated by CHI severity. Participants were 105 school-aged children in the chronic stage of CHI, divided into mild, moderate, and severe injury severity groups, and further subdivided according to frontal lobe injury. Outcome indices were imperfectly correlated in the group as a whole, although several relations between neurocognitive tests and parent ratings were observed within CHI subgroups. Different domains of cognitive function had different predictors. For attentional-inhibitory control, age at injury and time since injury were most predictive of outcome; for social discourse, predictors were injury severity and frontal lobe injury moderated by injury severity. Variability in cognitive outcome after childhood CHI is not random, but appears related to age, time, and biological features of the injury.

Understanding of literal truth, ironic criticism, and deceptive praise following childhood head injury

Children with closed head injury (CHI) have semantic-pragmatic language problems that include difficulty in understanding and producing both literal and nonliteral statements. For example, they are relatively insensitive to some of the social messages in nonstandard communication as well as to words that code distinctions among mental states. This suggests that they may have difficulty with comprehension tasks involving first- and second-order intentionality, such as those involved in understanding irony and deception. We studied how 6- to 15-year-old children, typically developing or with CHI, interpret scenarios involving literal truth, ironic criticism, and deceptive praise. Children with severe CHI had overall poorer mastery of the task. Even mild CHI impaired the ability to understand the intentionality underlying deceptive praise. CHI, especially biologically significant CHI, appears to place children at risk for failure to understand language as externalized thought.

Cortical thickness of the frontopolar area in typically developing children and adolescents

The development of the frontopolar cortex (FPC) through late childhood and adolescence was investigated using measures of cortical thickness. T(1)-weighted structural MRIs from 35 typically developing participants aged 8-20 years were used to construct 3D models of the brain, from which cortical thickness was measured. There was a significant inverse association between age and cortical thickness, such that cortical thickness decreased as age increased between 8 and 20 years. There was no effect of laterality or gender on cortical thickness.

A model of neurocognitive function in spina bifida over the life span

Spina bifida myelomeningocele (SBM), a neural tube defect that is the product of a complex pattern of gene-environment interactions, is associated with naturally occurring, systematic variability in the neural phenotype and in environmental factors that lead to systematic variability in the cognitive phenotype. We characterize the basis for variability in the cognitive phenotype of children with SBM with reference to a model of key biological, cognitive, and environmental events unfolding over the course of development from infancy to middle age. The cognitive phenotype is not domain-specific, but represents manifestations of unobservable constructs involving associative and assembled processing, the latter directly reflecting the impact of the neural phenotype on core deficits involving movement, timing, and attention orienting. The expression of the cognitive phenotype is variable, being moderated by features of the neural phenotype involving secondary CNS insults (such as hydrocephalus) that impair assembled processing, as well as by environmental factors (such as poverty, parenting, and education) that impair associative processing. The preservation of strengths in associative processing depends in part on the severity of the CNS deficits in SBM and the impact of the environment.

Changes in Working Memory after Traumatic Brain Injury in Children

The impact of traumatic brain injury (TBI) on working memory (WM) was studied in 144 children (79 with mild, 23 with moderate, and 42 with severe injuries) who underwent magnetic resonance imaging (MRI) at 3 months and were tested at baseline and at 3, 6, 12, and 24 months postinjury. An n-back WM task for letter identity was administered with memory load ranging from 1- to 3-back and a 0-back condition. A TBI Severity x Quadratic Tune interaction showed that net percentage correct (correct detections of targets minus false alarms) was significantly lower in severe than in mild TBI groups. The Left Frontal Lesions x Age interaction approached significance. Mechanisms mediating late decline in WM and the effects of left frontal lesions are discussed.

Prediction of cognitive sequelae based on abnormal computed tomography findings in children following mild traumatic brain injury

OBJECT The aim of this study was to determine whether the presence of intracranial pathophysiology on computed tomography (CT) scans obtained within 24 hours of mild traumatic brain injury (MTBI) in children adversely affects neuropsychological outcome during the 1st year postinjury. METHODS A prospective longitudinal design was used to examine the neuropsychological outcomes in children (ages 5-15 years) who had been treated for MTBI, which was defined as a loss of consciousness for up to 30 minutes and a lowest Glasgow Coma Scale (GCS) score of 13-15. Exclusion criteria included any preinjury neurological disorder. Outcome assessments were performed within 2 weeks and at 3, 6, and 12 months postinjury. Outcomes were compared between patients with MTBI whose postinjury CT scans revealed complications of brain pathophysiology (32 patients, CMTBI group) and those with MTBI but without complications (48 patients, MTBI group). RESULTS Significant interactions confirmed that the pattern of recovery over 12 months after injury differed depending on the intracranial pathology, presence and severity of injuries to body regions other than the head, preinjury attention-deficit hyperactivity disorder (ADHD), and socioeconomic status. Children in the CMTBI group had significantly poorer episodic memory, slower cognitive processing, diminished recovery in managing cognitive interference, and poorer performance in calculating and reading than patients in the MTBI group. Among the patients with mild or no extracranial injury, visuomotor speed was slower in those in the CMTBI group; and among patients without preinjury ADHD, working memory was worse in those in the CMTBI group. CONCLUSIONS Neuropsychological recovery during the 1st year following MTBI is related to the presence of radiographically detectable intracranial pathology. Children with intracranial pathology on acute CT performed more poorly in several cognitive domains when compared with patients whose CT findings were normal or limited to a linear skull fracture. Depending on the presence of preinjury ADHD and concomitant extracranial injury, working memory and visuomotor speed were also diminished in patients whose CT findings revealed complications following MTBI. Computed tomography within 24 hours postinjury appears to be useful for identifying children with an elevated risk for residual neuropsychological changes.

Attention Problems and Executive Functions in Children With Spina Bifida and Hydrocephalus

This study addressed the incidence of Attention-Deficit/Hyperactivity Disorder (ADHD) subtypes in children with spina bifida meningomyelocele and shunted hydrocephalus (SBH) as well as differences in executive functions among these subtypes. Parent rating scales revealed that 31% of the group with SBH could be identified with AD/HD, mostly the Inattentive type (23%). The group with SBH differed from normal controls on cognitive measures of executive functions, but subtype differences were not significant. Multivariate tests showed that children with SBH were rated with greater difficulties on the Behavior Rating Inventory of Executive Function (BRIEF) compared to controls; those with SBH and any subtype of ADHD differed from those with SBH and no ADHD; and those with ADHD (Combined Type) differed significantly from those with ADHD (Predominantly Inattentive Type). Subtype differences on univariate tests in the latter comparison were significant on the BRIEF Inhibit scale, showing more disinhibition in those with SBH and ADHD (Combined Type), but no significant differences were apparent on the BRIEF Sustain, Shift, and Initiate scales. The results show that the incidence of ADHD in children with SBH exceeds the population rate, is represented by problems with inattention rather than with impulsivity and hyperactivity; and that as with non-brain injured individuals, subtype differences in cognitive function remain to more clearly delineated.