Neurodevelopmental Disorders

Research challenges and solutions

Jo Van Herwegen, Deborah Riby, Jo Van Herwegen, Deborah Riby

• Publisher: Psychology Press
• Year: 2014
• ISBN:
  9781317563594
• Edition: 1
• Topic: Psychologie
• Subtopic: Histoire et théorie en psychologie

Interest in the field of neurodevelopmental disorders has grown exponentially in recent years across a range of disciplines, including psychology, psychiatry, education and neuroscience. The research itself has become more sophisticated, using multidisciplinary methods to probe interdisciplinary questions. Neurodevelopmental Disorders: Research Challenges and Solutions provides a thorough overview of the key issues involved in researching neurodevelopmental disorders.

The volume includes 14 chapters, arranged over three sections. Chapters in the first section address general research challenges for the study of neurodevelopmental disorders. The second section draws upon specific disorders (such as Williams syndrome, Autism Spectrum Disorders, Down Syndrome, Fragile X Syndrome, ADHD, and Language Disorders) to consider the syndrome-specific issues or challenges that may be crucial to advancing our understanding of aspects of cognition and behavior associated with them. The final section considers how research evidence may be translated into practice to begin making an impact upon the lives of individuals who have neurodevelopmental disorders and their families. Each chapter in the book also includes 'practical tips' for either conducting research with individuals who have neurodevelopmental disorders or considering wider practical issues.

The book will be indispensable reading for advanced students, researchers, and practitioners in the fields of developmental psychology, developmental psychopathology, special needs education, neuropsychology, and neurodevelopmental disorders.

Part I
General research challenges

1
Neurodevelopmental Disorders

Definitions and issues

Jo Van Herwegen, Deborah Riby and Emily K. Farran

1.1 Introduction

Neurodevelopmental disorders are different from acquired disorders in that for the latter the cause or the onset can happen during any time of a person’s lifespan. A crucial component of neurodevelopmental disorders is that individuals show difficulties from birth onwards and the cause is often situated during gestation or birth. The term ‘neurodevelopmental’ disorder has seen an increased use over the past two decades (Bishop & Rutter, 2006), yet it is often used to cover a wide variety of meanings and disorders. Some, for example, have used the term in a very restricted sense to refer only to those conditions that affect children’s neurological development with a known genetic or acquired etiology, such as Fragile X syndrome (FXS) or fetal alcohol syndrome. However, others have taken a broader definition of neurodevelopmental disorders and included those conditions presumed to be of multifactorial etiology, such as Autism Spectrum Disorders (ASD), developmental dyslexia and Attention Deficit Hyperactivity Disorder (ADHD). The current DSM 5 criteria are even broader and include all developmental disorders; intellectual disabilities, communication disorders, ASD, ADHD, specific learning disorders, motor disorders (including developmental coordination and movements disorders, Tourette’s, and tic disorders), and other specified and unspecified neurodevelopmental disorders. Similarly, ICD-10 refers to disorders of psychological development and includes developmental disorders of speech and language, scholastic skills and motor function. The ICD-10 also includes pervasive developmental disorders (this includes ASD and Rett’s syndrome). Therefore, the work that is of relevance to this field is broad in its coverage of atypical development.

In this chapter (and throughout the current text), we will refer to neurodevelopmental disorders as those disorders that are of a genetic or multifactorial origin that result in one or more specific cognitive deficits. These deficits are present early in life and extend into adult life without showing relapse or remission. This therefore excludes acquired disorders, such as fetal alcohol syndrome, acquired motor disorders, or disorders that are akin to remissions, such as schizophrenia and anti-social behaviours.

1.2 The importance of researching neurodevelopmental disorders

The most important reason to study neurodevelopmental disorders is to obtain a better understanding that can subsequently inform better (more accurate) diagnosis and in turn lead to more successful training programmes or interventions. A more thorough understanding of neurodevelopmental disorders not only requires a description of the behavioural and biological aspects of a disorder, but the cognitive or psychological processes must be examined as these mediate the link between the brain and behaviour (see Chapters 2, 5 and 6 for discussion of some of these issues). One framework that incorporates all three levels (e.g. biological, cognitive and behavioural), as well as environmental factors, is the causal model by Morton and Frith (1995). This model aims to provide full causal explanations for neurodevelopmental disorders, incorporating developmental aspects to allow evaluation of different competing causal accounts for specific disorders. Yet, as we will discuss below there are a number of challenges and complexities typical to most disorders which challenge such causal frameworks.

Second, research in neurodevelopmental disorders is vital in order to advance our theoretical understanding of typical developmental (TD) pathways and cognition in general. For example, it has been argued that infants are born with certain core systems for knowledge (Spelke & Kinzler, 2007). One core domain that has been well-researched in infants is number development. Research has shown that six-month-old infants can discriminate between large numerosities using their approximate number system and that this system is more predictive of number abilities later in life. In contrast, it has been argued that discrimination between small numbers is related to an object file system which is more akin to memory abilities (Feigenson, Dehaene & Spelke, 2004). Yet, as both core systems are already present in TD infants these studies can only show correlations between the early discrimination abilities and number development later in life. In contrast, neurodevelopmental disorders are often associated with uneven cognitive profiles with performance on certain cognitive abilities outperforming others. Therefore, neurodevelopmental disorders provide the perfect opportunity to investigate more subtle associations, or what abilities underlie successful performance on certain tasks. For example, studies have shown that participants with Williams syndrome (WS) perform better on number tasks that include verbal abilities, such as counting tasks, but perform worse on tasks that tap into the magnitude system or approximate number system (ANS). This pattern contrasts with that seen in Down syndrome (DS) where individuals show the opposite pattern (Ansari et al., 2003; Ansari, Donlan & Karmiloff-Smith, 2007; Paterson, Girelli, Butterworth & Karmiloff-Smith, 2006). A recent study by Karmiloff-Smith and colleagues (2012a) showed that, although infants with WS were able to discriminate between two and three dots, they could not discriminate between large numerosities such as eight and sixteen dots. Infants with DS on the other hand showed the opposite pattern. Yet, direct comparisons between older children and adults with DS and WS have demonstrated that those with DS have overall better number abilities compared to those with WS (Paterson et al., 2006). This evidence suggests that the ability to discriminate between large numerosities or the magnitude system is a better predictor for number outcomes later in life than the object file system (but see discussion in Chapter 2). This is important for our understanding of typical development because it can lead to better training and intervention programmes. Indeed, recent studies of TD children and adults have shown that training of ANS abilities positively impacts on overall mathematical abilities (Dewind & Brannon, 2012; Park & Brannon, 2013; Van Herwegen, Costa & Passolunghi, submitted).

Therefore, as illustrated by the area of number development, the study of developmental disorders not only informs knowledge of these disorders per se, but can also inform our understanding of the ‘typical’ path of development in individuals who do not have a disorder of development. The theoretical contribution that research within the field of developmental disorders can make is vast. However, to make both theoretical and applied contributions to knowledge there are a number of methodological issues that require consideration. These issues will be discussed across a number of chapters within this volume and the discussion below is a summary of some of the main issues to be addressed.

1.3 Critical issues when researching neurodevelopmental disorders

1.3.1 The need to study development and related issues

Research in the field of neurodevelopmental disorders has historically adopted models used for adult brain-damaged patients (for a detailed discussion see Chapter 2). For example, evidence from double dissociations has repeatedly been used to show that certain cognitive abilities can be either spared or impaired and thus, can exist independently from each other – which led to the development of theories of ‘modularity of mind’ by Fodor (1983). A frequently mentioned example of such a double dissociation in neurodevelopmental disorders is the fact that language abilities outperform non-verbal intelligence abilities in WS, in contrast to individuals with Specific Language Impairment (SLI) who show language difficulties in the absence of any general intelligence deficits (Pinker, 1999; though for further discussion on this issue see Chapter 8). Yet, notions of double dissociations are static and claims that the brain exists of specific modules are based on studies investigating the brain in its mature state. Recently, more subtle matching methodologies have suggested that it is highly unlikely that any area of functioning can be ‘intact’ and have instead suggested that neurodevelopmental disorders can be described in terms of relative proficiencies and deficits.

Additionally, studies that have investigated cognitive abilities in infants have shown that the course/pathway of development in neurodevelopmental disorders is often atypical. For example, while typically developing children generally point before they start speaking infants with WS only point after the emergence of their first word (Laing et al., 2002). In addition, it is less clear how the infant brain is structured and how the endstate is the result of developmental processes (Karmiloff-Smith, Scerif & Ansari, 2003). A recent view of cognitive development is that the specialisation of brain structures is the result of brain maturation over development through interaction with the environment, genes, brain and behaviour (Thomas, 2003). Thus, advocates of a neuroconstructivist approach have provided strong evidence that a more developmental approach is required when studying neurodevelopmental disorders (see discussion in Chapter 2; Karmiloff-Smith, 1998, 2009; Farran & Karmiloff-Smith, 2012; Thomas, Baughman, Karaminis & Addyman, 2012).

One reason why a developmental approach is needed is the fact that the brain changes over time. Brain plasticity is often defined as changes to the brain system as a result of external (environmental) or internal (brain damage) factors (Huttenlocher, 2002). Plasticity of the brain is larger in children than in adults, which is evidenced by the fact that children recover better and faster after brain damage compared to adults (but see Thomas, 2003, for a discussion). This means that subtle differences over time can impact the development of cognitive abilities. This is especially true for specialisation of the brain in neurodevelopmental disorders:

brain volume, brain anatomy, brain chemistry, hemispheric asymmetry and temporal patterns of brain activity are all atypical […]. How could the resulting system be described as a normal brain with parts intact and parts impaired, as the popular view holds? Rather, the brains of infants with [neurodevelopment disorders] develop differently from the outset, which has subtle, widespread repercussions.

(Karmiloff-Smith, 1998, p. 393)

As a consequence, a developmental approach is required to study neuro-developmental disorders.

More developmental approaches have emerged within the field of neurodevelopmental disorders in recent years. First, research studies have started to adopt more developmental research methods, including inclusion of wider age ranges and tracing development back to infancy, and are gradually using fewer matched group designs. For example, in the past studies of neurodevelopmental disorders often investigated narrow age ranges and matched groups of neurodevelopmental disorders to control groups (e.g. typically developing individuals or other neurodevelopmental disorders) based on either chronological age or mental age abilities. Such approaches are common in adult neuropsychology but again they represent a static timepoint in development in that they do not capture any of the changes over time. In addition, matching participants with neurodevelopmental disorders to a typically developing control group based on chronological age (CA) often underestimates the disorder group, as disorder groups rarely perform at their CA level. However, matching groups on mental age requires groups to be matched on a specific standardised task, for example matching groups on their receptive vocabulary using the British Picture Vocabulary Scale (Dunn, Dunn, Whetton & Burley, 1997), or the Ravens Coloured Progressive Matrices task (RCPM: Raven, Court & Raven, 1990). Not only does this mean that the matching is theoretically driven, which can interfere with the findings of the study, depending on what abilities the groups are matched, performance in the disorder group will again be under- or over-estimated, due to the often uneven cognitive profiles of neurodevelopmental disorders (see Thomas et al., 2009 for a discussion). Finally, matching studies often apply the rule that two groups are matched when their performance is not significantly different (or p value is larger than 0.05). Yet, the question is how matched the two groups really are as differences in performance often have to be quite large in order for the statistical result to be significant and statistically non-significant group differences might still include large differences and significance in the real world.

The best developmental solution to a matching approach is to study cognitive changes in neurodevelopmental disorders over development using longitudinal studies. Yet, longitudinal studies are time consuming and often expensive. An alternative method that is becoming frequently used is that of a developmental trajectory or cross-sectional approach in which different participants across a large age range are examined and trajectories of the neurodevelopmental group are compared to those of the control group (see Thomas et al., 2009). Yet, the developmental trajectory approach is not without criticism and recent studies have shown that outcomes from cross-sectional studies differ from those using longitudinal designs (see discussion in Chapter 10; Cornish, Cole, Longhi, Karmiloff-Smith & Scerif, 2013). Cross-sectional studies include snapshots of cognitive abilities across different age groups and thus the individual differences between these individuals might mask any real changes over time across an entire group. As a result, although cross-sectional studies can give an indication of the developmental profile in neurodevelopmental disorders, these studies should be followed up by longitudinal research. In addition, other difficulties for crosssectional studies include the fact that standardised tasks need to include a wide age range in order to avoid floor and ceiling effects between the two groups (see the discussion in Thomas, Purser & Van Herwegen, 2012) and importantly, this design assumes that individuals with the same disorder will follow the same developmental trajectory (this may not always be the case: see Chapter 7 for a discussion of heterogeneity within disorders and Little et al., 2013 for a study using cluster analysis to explore variability within one disorder group).

A second developmental trend in recent studies is the examination of domain-general abilities (such as eye movement behaviour, attention, processing speed, cognitive control, memory abilities, etc.) and how these building blocks affect the development of cognitive abilities later in life. This is important in that even when development in neurodevelopmental disorders appears to be within the typical range, because of plasticity and compensation strategies in the brain, this behaviour might be reliant upon alternative cognitive strategies or abilities. For example, individuals with WS are often reported to have relatively good face processing abilities on some aspects of recognition, despite their lower general intelligence. Yet studies have shown that they rely upon atypical strategies to complete basic face re...