Development of the adolescent brain: implications for executive function and social cognition Sarah-Jayne Blakemore 1 and Suparna Choudhury 2 1 Institute of Cognitive Neuroscience, Department of Psychology, University College London, UK; 2 Behavioural & Brain Sciences Unit, Institute of Child Health, University College London, UK Adolescence is a time of considerable development at the level of behaviour, cognition and the brain. This article reviews histological and brain imaging studies that have demonstrated specific changes in neural architecture during puberty and adolescence, outlining trajectories of grey and white matter development. The implications of brain development for executive functions and social cognition during puberty and adolescence are discussed. Changes at the level of the brain and cognition may map onto behaviours commonly associated with adolescence. Finally, possible applications for education and social policy are briefly considered. Keywords: Adolescence, brain development, cognition, puberty, social cognition. Adolescence is a time characterised by immense hormonal and physical changes (Coleman & Hendry, 1990; Feldman & Elliott, 1990). This transition from childhood to adulthood is also characterised by dramatic changes in identity, self-consciousness and cognitive flexibility (Rutter & Rutter, 1993). There seems to be a qualitative shift in the nature of thinking such that adolescents are more self-aware and self-reflective than prepubescent children. Ado- lescents develop a capacity to hold in mind more multidimensional concepts and are thus able to think in a more strategic manner. Empirical research on cognitive and neural development during puberty and adolescence is in its initial stages. In the past few years, several pioneering experiments have investigated the development of brain and cognitive processes during this period of life. This review begins by describing the cellular studies that first demonstrated anatomical brain develop- ments during adolescence. It then describes how re- cent brain imaging techniques have supported these findings and have shed some light on the trajectories of structural brain maturation during adolescence. The following sections discuss investigations of cog- nitive development, in particular studies of executive functions and social cognition using behavioural and functional imaging techniques. Finally, applications for education and social policy are briefly suggested. The first experiments on adolescent brains Until recently, very little was known about brain development during adolescence. The notion that the brain continues to develop after childhood is relat- ively new. Experiments on animals, starting in the 1950s, showed that sensory regions of the brain go through sensitive periods soon after birth, during which time environmental stimulation appears to be crucial for normal brain development and for normal perceptual development to occur (Hubel & Wiesel, 1962). These experiments suggested the human brain might be susceptible to the same sensitive periods in early development. Indeed, later experi- ments demonstrated sensitive periods in the first year of life for sensory capacities such as sound categorisation (Kuhl, Williams, Lacerda, & Stevens, 1992). Based on these experiments, the idea that the human brain may continue to undergo substantial change after early sensitive periods seemed unlikely. It was not until the late 1960s and 1970s that research on post-mortem human brains revealed that some brain areas, in particular the prefrontal cortex, continue to develop well beyond early child- hood. Studies carried out in the 1970s and 1980s demonstrated that the structure of the prefrontal cortex undergoes significant changes during puberty and adolescence (Huttenlocher, 1979; Huttenlocher, De Courten, Garey, & Van Der Loos, 1983; Yakovlev & Lecours, 1967). Two main changes were revealed in the brain be- fore and after puberty. As neurons develop, a layer of myelin is formed around their extension, or axon, from supporting glial cells. Myelin acts as an insul- ator and massively increases the speed of transmis- sion (up to 100 fold) of electrical impulses from neuron to neuron. Whereas sensory and motor brain regions become fully myelinated in the first few years of life, although the volume of brain tissue remains stable, axons in the frontal cortex continue to be myelinated well into adolescence (Yakovlev & Le- cours, 1967). The implication of this research is that the transmission speed of neural information in the frontal cortex should increase throughout childhood and adolescence. The second difference in the brains of pre-pub- escent children and adolescents pertains to changes Journal of Child Psychology and Psychiatry 47:3/4 (2006), pp 296–312 doi:10.1111/j.1469-7610.2006.01611.x Ó 2006 The Authors Journal compilation Ó 2006 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