Abstract
Zusammenfassung: Numerische Kenntnisse bilden ein wichtiges Fundament für die schulische und berufliche Entwicklung. Viele Kinder leiden jedoch unter großen Schwierigkeiten beim Erlernen numerischer Kompetenzen und werden oft mit einer «entwicklungsbedingten Dyskalkulie» diagnostiziert. Eine wachsende Anzahl von Studien mit Hilfe bildgebender Verfahren zeigt nun, dass spezifische Regionen im Gehirn von Kindern mit Dyskalkulie einen atypischen Entwicklungsverlauf beim Erlernen basisnumerischer Kompetenzen – wie dem Vergleichen numerischer Mengen – aufweisen. Diese Studien deuten somit auf eine domänenspezifische Ursache der Rechenschwäche hin. In der vorliegenden Übersichtsarbeit möchten wir die Befunde zur typischen und atypischen Gehirnentwicklung der Zahlenverarbeitung von einer neurowissenschaftlichen Perspektive diskutieren. Weiters werden wichtige Implikationen für Diagnostik und Intervention besprochen.
Neurocognitive Foundations of Typical and Atypical Number Development
Background: The acquisition of basic mathematical abilities represents an essential component of leading a successful and healthy life in modern societies. While the majority of children are able to learn basic numerical concepts rather effortlessly, some children display severe difficulties in acquiring basic number skills (such as being able to rapidly retrieve the answers to basic arithmetic problems). Children with persistent difficulties in basic numerical processing in concert with otherwise relatively normal verbal and non-verbal intelligence are referred to as children with ’Developmental Dyscalculia’ (DD). In comparison to the vast amount of literature on ’Developmental Dyslexia’, which is a specific developmental difficulty in acquiring reading skills, little is know about the causes of DD. Notwithstanding, recent technological and methodological advances in imaging the human brain – such as functional Magnetic Resonance Imaging (fMRI) – have fostered a new line of research that seeks to understand the brain mechanisms associated with the typical and atypical development of numerical competencies. These new insights point to potential causal, neurobiological factors in DD and pave the way towards new investigations of the typical and atypical developmental trajectories of number development through the combined use of behavioral and neuroimaging methods.
Aims: Against this background, the main purpose of the present paper is to provide an accessible introduction and review of the state-of-the-art understanding of the neural correlates associated with both typical and atypical number development. In view of this the review will also assess the utility of a cognitive neuroscience approach to better understand how children both succeed and fail at acquiring numerical and mathematical skills.
Methods: To achieve these objectives, the presented paper reviews and critically discusses empirical investigations with both adults and children that have used functional and structural Magnetic Resonance Imaging (MRI) and/or event-related potential (ERP) to investigate the neural basis of basic numerical abilities, such as estimating and comparing numerical magnitudes. More specifically, an overview of the present empirical evidence from studies with adults suggests that the intraparietal sulcus (IPS) within the parietal lobe is a key structure for representing and processing numerical magnitudes. Having presented the neural correlates of numerical magnitude processing in adults, we will move on to discussing a growing body of research that has investigated the typical development of numerical processing in the child’s brain. This review will discuss studies with children and adults that have investigated to which extent the neural mechanisms underlying numerical processing change over the course of learning and development.
Results: The data of this developmental research suggests that the brain activation within the IPS during numerical magnitude processing tasks (such as number comparison) increases over developmental time. However, not only does activation within the IPS increase over the course of development, but furthermore, it has been found that activation in frontal areas – which are commonly associated with executive functions, cognitive control and working memory – decreases with age. Convergent with these developmental changes in brain activation researcher have recently suggested that the brain undergoes an ontogenetic specialization for representing numerical magnitudes within the IPS. This process of ontogenetic specialization reflects an increasingly fluent processing of numerical magnitudes within the IPS, which requires less augmentation by prefrontal resources that are engaged when number processing is effortful and immature. Having reviewed the literature on the neural correlates of number processing in typically developing adults and children, the review will examine the extent to which the present literature suggests that brain function and brain structure in children with DD differs from brain function and brain structure in children without DD. Consistent with the hypothesis that DD is characterized by atypical activation of the IPS, we will review a series of studies that have shown that children with DD activate their IPS differently than their typically developing peers (though studies differ on whether more or less activation is exhibited by children with DD relative to their typical developing peers). These data suggest that children with DD may fail to specialize the IPS for basic number processing in the typical way, which deprives them of a crucial scaffold (fluent processing of numerical magnitude) to develop efficient, higher-level mathematical skills. In addition to a possible functional deficit within the IPS, a reduction in gray matter volume in children with DD has been found in areas in and around the IPS and thus both the structural and functional neuroanatomy of DD will be considered in this paper.
Discussion: Taken together, neuroscientific evidence suggests that the IPS – a structure that has been shown to be critical for basic numerical magnitude processing in adults and typically developing children – displays an atypical functional and structural development in children with DD. Thus it is plausible to argue that difficulties in mathematical competences may be associated with a deficit in representing numerical magnitudes within the IPS. These neuroscientific findings are consistent with a growing body of studies that suggest that, at least in part, the deficits that children with DD have in mental arithmetic are driven by their weaknesses in processing and representing numerical magnitude. In other words, early-developing, low-level numerical magnitude processing skills constrain the acquisition of higher-level calculation abilities. Much of the early work on atypical and typical number development was focused on mental arithmetic and the domain-general factors (such as working memory and speed of processing). While such work is undoubtedly important and will continue to constrain our understanding, the relatively more recent work, using both traditional methods from cognitive psychology and novel tools from cognitive neuroscience, is adding a new perspective to research on the ontogeny of typical and atypical number skills.
The paper concludes with a discussion of the potential implication of the cognitive neuroscience approach to the study of typical and atypical number development for the design and implementation of new diagnostic/screening tools and early intervention for children who might be at risk of developing DD.
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