Why it's never too late to grow

10th August 2007 at 01:00
Small children don't need cramming and teenagers are not as unreceptive as they seem. Sarah-Jayne Blakemore looks at the development of the human brain from birth to adolescence

A few decades ago, many people would have found it hard to believe that the brain changes after early childhood. Some would even have argued that it was largely fixed by the age of three. Now, due to recent research using modern brain-imaging techniques, we know better. Some brain regions, in particular the frontal cortex, continue to develop during adolescence and beyond.

It is probably dramatic transformations in the brain, not just hormones, that create the typically moody, uncommunicative teenager and may also cause the dip in performance that affects some pupils in Year 8.

Much has been known about early brain development since experiments on animals carried out in the 1950s and 1960s. One major developmental process affects the "wiring" of brain cells (neurons) the intricate network of connections (synapses) between them.

Early in development, the brain begins to form new synapses, so many in fact that the number of connections in a baby's brain greatly exceeds adult levels. This process, known as synaptogenesis, is followed by a period of pruning (or synaptic elimination) in which excess connections wither away.

The research showed that synaptic pruning can be influenced by the particular environment an animal experiences. Synapses that are frequently used are strengthened, while infrequently-used synapses are eliminated the "use it or lose it" phenomenon. The early animal experiments demonstrated that these processes are mostly over by about three, at least in sensory regions of monkeys' brains.

On the basis of this research, educational literature often suggests that the crucial phase of brain development in humans occurs as early as from birth to three years and that during this time children should be exposed to hot housing and formal education.

However, this argument neglects the fact that monkeys do not go through the same extended developmental period as humans and are sexually mature by the age of three1. Indeed, research carried out in the 1970s and 1980s demonstrated that the timetable for synaptogenesis and synaptic pruning is not the same for humans as it is for monkeys.

In the late 1970s, Peter Huttenlocher at the University of Chicago collected post-mortem brains from humans of all ages and found that the frontal cortex was remarkably different in the brains of pre-pubescent children and post pubescent adolescents2.

While in sensory brain areas the number of synapses has reached mature levels by mid-childhood, there is a second wave of synaptic reorganisation in the frontal cortex that starts at around the onset of puberty.

The frontal cortex governs cognitive abilities, such as making plans, remembering to do things in the future, multi-tasking and inhibiting inappropriate behaviour. It also governs self-awareness and understanding others. Huttenlocher's findings have been confirmed by recent research using non-invasive brain imaging techniques such as Magnetic Resonance Imaging (MRI). In the past decade, several MRI studies, which have acquired brain scans from hundreds of people of different ages, have consistently shown that the volume of grey matter in the frontal cortex increases gradually during childhood and peaks at around the onset of puberty about 11 in girls and 12 in boys3.

This is followed by a gradual decrease in grey matter during adolescence and early adulthood. Grey matter contains synapses, and so changes are thought to reflect alterations in the number of synapses in a particular brain region.

These findings have important implications for education. First, there is no need to "hot-house" young children. Contrary to much popular belief, there is no convincing neuroscientific case for starting formal education as early as possible. Second, teenagers may seem surly and unreceptive, but the brain is still adaptable during adolescence, so education is crucial at this time. It's not too late to learn

Dr Sarah-Jayne Blakemore is a cognitive neuroscientist at Univerity College London

Further reading

1 Blakemore, S. J., Frith, U. The Learning Brain: Lessons for Education. Blackwell (2005)

2 Huttenlocher, P. R. et al (1983). Synaptic development in human cerebral cortex. International Journal of Neurology, 16-17, 144-154

3 Toga A. W., Thompson P. M., Sowell E. R. (2006) Mapping brain maturation, Trends in Neuroscience. 29(3) 148-159

See also Neuroscience and Education: Issues and Opportunities, by the Teaching and Learning Research Programme, which can be downloaded at www.tlrp.org

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