Trends in Cognitive Sciences
Mapping brain maturation and cognitive development during adolescence
Introduction
Adolescence represents a major transition that takes place over most of the second decade of human life. It is the final phase of a prolonged pattern of growth and maturation, which have emerged late in the evolution of our species and may confer an evolutionary advantage by providing ample time for the maturation of the brain and its cognitive apparatus before it reaches the full potential of a young adult (e.g. 1, 2, 3). In the shift from a caregiver-dependent child to a fully autonomous adult, the adolescent undergoes multiple changes in physical growth, physiology, and cognitive and emotional skills. As reviewed in the accompanying article by Steinberg [4], the interface between affect, reasoning and decision making, and action is one of the vital elements in adolescent development. This review focuses on current trends in the use of non-invasive techniques for brain mapping to further our understanding of brain–behaviour relationships during this period of human development. This is the first step towards studying the forces present in the subject's environment and/or genome that act on the neural substrate underlying complex behaviours of an adolescent.
Recent technological and conceptual advances have dramatically increased our ability to relate structural and functional maturation of the adolescent brain to that of the adolescent's behaviour. On the technology side, magnetic resonance imaging (MRI) represents a major advance; it allows us to measure in vivo subtle inter-individual differences in brain structure and to assess activity in distinct neural circuits from birth to adulthood. The concept of modular organization of the primate cerebral cortex is, arguably, the most fruitful heuristic framework for mapping function onto structure: distinct areas of the cortex specialize in processing different types of information while sharing it via specific neural circuits (reviewed in [5]). In this context, the importance of neural connectivity for smooth communication across specialized brain regions is increasingly recognized. These technological and conceptual advances go hand in hand. Brain mapping provides accurate localization of structural and functional changes in specialized grey-matter regions, as well as the assessment of structural and functional integrity of white-matter pathways that connect them. Put together with the ‘modular-circuit’ view of the primate brain, we can start mapping maturational changes in brain–behaviour relationships during adolescence.
Section snippets
Brain structure during adolescent development
Over the past decade, structural-MRI studies have provided the first comprehensive picture of age-related changes in the volume of grey and white matter of typically developing children and adolescents. These studies provide T1-weighted (T1W), T2-weighted (T2W) and proton-density-weighted (PDW) images of the brain (Box 1).
Structural images are colour-coded representations of MR signals measured throughout the brain and localized into individual 3D elements of the brain image (voxels). It is
Brain function during adolescence
The ultimate goal of research in this area is to understand how the human brain implements behaviour throughout the life span. Two general strategies are used to achieve this goal: (1) perturbation, and (2) correlation. Early brain lesions are the only model of region-specific perturbations used, albeit in a limited manner, in human developmental studies (see, for example, studies of early frontal-lobe lesions and aggression (e.g. [23]). On the other hand, advances in MRI have opened up
Challenges and future directions
Adolescence is a fascinating period of human development: the struggle for identity, choice of friends and first sexual partners, academic routes and vocations are but a few examples of complex behaviours that the brain must implement at the brink of adulthood. Today, we have an extensive range of tools that allow us to measure brain structure and function. This review has emphasized magnetic resonance imaging but there are many other techniques, most notably electro- and
Acknowledgements
The work and ideas expressed in this article arose over many years through interactions with my colleagues at the Brain Imaging Center of the Montreal Neurological Institute (Drs. Collins, Evans, Pike, Worsley and Zijdenbos), the MNI Cognitive Neuroscience Unit (Drs. Leonard, Milner, Petrides and Zatorre), the Child Psychiatry Branch of the National Institute of Mental Health (Drs. Giedd and Rapoport) and, most importantly, students and fellows in my laboratory. I would like to thank in
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