Assignment: scope of neuropsychological theory

Assignment: scope of neuropsychological theory

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Assignment: The scope of neuropsychological theory

How neuropsychology informs our understanding of developmental disorders

Bruce F. Pennington University of Denver, USA

This review includes 1) an explanation of what neuropsychology is, 2) a brief history of how develop- mental cognitive neuroscience emerged from earlier neuropsychological approaches to understanding atypical development, 3) three recent examples that illustrate the benefits of this approach, 4) issues and challenges this approach must face, and 5) a forecast for the future of this approach. Keywords: Developmental cognitive neuroscience, plasticity, molecular genetics, neural network models, dyslexia, neuropsychology.

This paper will present neuropsychology as a method for understanding childhood disorders. Very simply put, neuropsychology is the study of brain–behavior relations, and developmental neuropsychology is the study of how those relations develop in both typical and atypical cases. More recently, with advances in neural network models, neuroimaging, and genetics, a field of developmental cognitive neuroscience has emerged that tests links across several levels of analysis: etiology, brain development, neuropsy- chology, and behavioral symptoms. So, I will argue that neuropsychology provides an important bridge across these levels and thus among the other methods described in other articles in this Annual Research Review. As it interacts with these other methods,neuropsychology itself isbeing transformed, and will eventually merge into the wider inter- discipline of developmental cognitive neuroscience.

This review includes 1) an explanation of what neuropsychology is, 2) a brief history of how devel- opmental cognitive neuroscience emerged from earlier neuropsychological approaches to under- standing atypical development, 3) three recent examples that illustrate the benefits of this approach, 4) issues and challenges this approach must face, and 5) a forecast for the future of this approach.

What is neuropsychology?

Since the traditional role of neuropsychology has mainly been to understand the behavioral effects of acquired lesions in adults, it has always been a clinical science that has attempted to explain behavioral symptoms in terms of theories of normal brain function. So neuropsychology illustrates well the reciprocal relation that exists between basic and clinical science. We cannot understand clinical phenomena without a theory of normal function, but clinical phenomena sometimes force revisions in our theories of normal function. The history of neuro-

psychology provides many noteworthy examples of both parts of this dialectic: how basic cognitive theory has been revised in response to unexpected clinical data and how advances in basic cognitive theory have changed the constructs and measures clinical neuropsychologists use to understand patients. Patient data have led to theoretical revi- sions in virtually every domain of cognition: vision, attention, long-term memory, short-term memory, language, and reading (McCarthy & Warrington, 1990; Shallice, 1988; Squire, 1987). In each case, the observation of a surprising set of symptoms in a patient leads to much more detailed experimental investigations, and then to revisions of basic theory. Modern cognitive science would surely be quite different without the data provided by patients with acquired lesions, yet modern neuropsychology would not exist without modern cognitive science. For instance, contemporary clinical neuropsycho- logists, unlike those of a few decades ago, think in terms of interacting neural systems and are much more cognizant of the brain’s plasticity in the face of damage.

More recently, the application of neuropsychology to adult and child psychopathology has expanded the scope of neuropsychological theory to include domains like affective decision-making, inhibition, social cognition, imitation, emotion regulation, source-monitoring of thoughts and actions, and even the self. So there is no sharp line between neuro- psychological and psychological explanations of behavior. Neuropsychology just adds the additional requirement that we try to understand psychological processes in terms of how the brain works. Hence, neuropsychologists mainly use behavioral measures in their work, but they often relate such measures to measures of brain structure or function, or even to genetic measures.

So neuropsychology, like the rest of science, is solidly committed to materialism – behavioral phe- nomena result from complex physical interactions in the brain – but not necessarily to reductive materi- alism. That is, it is unlikely that we can reduceConflict of interest statement: No conflicts declared.

Journal of Child Psychology and Psychiatry 50:1-2 (2009), pp 72–78 doi:10.1111/j.1469-7610.2008.01977.x

� 2008 The Author Journal compilation � 2008 Association for Child and Adolescent Mental Health. Published by Blackwell Publishing, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA

phenomena like attention or memory to the behavior of individual neurons; instead, neuropsychology holds that such phenomena are an emergent prop- erty of the interactions among many neurons, and among networks of neurons. So we could say that neuropsychology is characterized by a commitment to ‘emergent materialism’ and is consequently com- mitted to interdisciplinary integration.

History

As is true in psychiatry and neurology generally, child neuropsychology began as the somewhat neglected stepchild of adult neuropsychology. Although interest in individual differences in brain– behavior relations has been part of neuropsychol- ogy since its beginnings in the early 19th century (Gall & Spurzheim, 1809), for the most part, clas- sical neuropsychology focused on the consequences of acquired lesions in adults and developed ‘box and arrow’ models of normal adult brain functions based on those findings. Only occasionally did these researchers consider childhood disorders. Freud (1897) wrote a monograph on cerebral palsy and Pringle-Morgan (1896) described developmen- tal dyslexia with the term ‘congenital word blind- ness.’ Hinshelwood (1917) elaborated this construct in a monograph with the same name. Based on cases of acquired dyslexia with similar symptoms, apparently caused by damage to, or disconnection from, the left angular gyrus (e.g., Dejerine, 1891), Hinshelwood (1917) speculated that a congenital problem in the angular gyrus caused developmental dyslexia. Hinshelwood thought of the angular gyrus as a memory center for visual word forms, a con- cept not too different from the construct of the fusiform word area identified by modern neuro- imaging, with the key difference that activity in the fusiform word area only emerges with increasing expertise in reading. Obviously, an innate center for reading per se would not make much evolutionary sense.

We can see in Hinshelwood’s theory of develop- mental dyslexia an example of a recurring problem in the application of neuropsychology to atypical development. Theories of brain–behavior relations based on discoveries in adults with acquired lesions were applied in a wholesale fashion to children. It did not occur to these early thinkers that brain–behavior relations might change over the course of develop- ment, as is true for the functions of the fusiform word area.