El cerebro adolescente (entrevista a Sarah-Jayne Blakemore)

Quizás el momento cumbre del desarrollo cerebral se de en la adolescencia. Esta etapa vital problemática, llena de grandes riesgos y oportunidades, el cerebro realiza su último gran desarrollo: el del lóbulo frontal. Durante el doloroso parto que constituye este proceso el niño que juega se convierte en adulto responsable, rompe la crisálida y echa a volar.

El proceso es ligeramente distinto en cada uno de nosotros, pero tienen todos y cada uno de esos procesos separados los suficientes elementos en común para que podamos considerarlos un mismo y único proceso biológico, de carácter universal.

Sarah-Jayne Blakemore, del University College de Londres, estudia el desarrollo del cerebro humano, poniendo especial atención al que acaece en el período de la adolescencia. Con test psicológicos y técnicas de neuroimagen observa circunspectamente como el cerebro pasa de una estructura y función infantiles a otras adultas,  cruzando el terreno minado emocionalmente de la transfiguración adolescente.

Ha escrito un libro junto con su colega Uta Frith sobre Cómo Aprende el Cerebro. Como lector entusiasta del mismo debo recomendarlo encarecidamente, en particular a aquellos que se dediquen profesionalmente a la educación.

La profesora Blakemore ha tenido la amabilidad de respondernos unas preguntas. José Miguel Guardia las puso en un correcto inglés.

En inglés:

1.- How does brain develop through the life cycle? What are the milestones of brain development?

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 neurons. Early in development, the brain begins to form new synapses, so that the synaptic density – the number of synapses per unit volume of brain tissue – greatly exceeds adult levels. This process of synaptic proliferation, ‘synaptogenesis’, lasts up to several months, depending on the species of animal.

The increase in the number of synapses is followed by a period of synaptic elimination (or pruning) in which excess connections wither away. This process is pre-programmed to a large extent – it will happen in all environments. However, the environment can also influence synaptic pruning, in that frequently used connections are strengthened and infrequently used connections eliminated.

This research suggested that brain development is particularly sensitive to environmental influence very early in life. It was not until the 1970s that research on post-mortem human brains revealed that some areas of the human brain, in particular the frontal cortex, continue to develop well beyond childhood. The frontal cortex is the area responsible for cognitive abilities such as the ability to make plans, remember to do things in the future, multi-task and inhibit inappropriate behaviour (executive functions). The frontal cortex also plays an important role in self-awareness and understanding other people. 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 adolescents. While in sensory brain areas such as the visual cortex, synaptogenesis and synaptic pruning occur relatively early and synaptic density has reached adult levels by mid-childhood, synaptic reorganisation in the frontal cortex continues much later, well into adolescence. Huttenlocher found that the number of synapses in the frontal lobe is high at around puberty, after which their number decreases (due to synaptic pruning) throughout adolescence.

Another developmental mechanism that occurs for several decades in the frontal cortex is myelination. As neurons develop, they build up a layer of myelin on their axon (the long fibre transmitting signals from each brain cell). Myelin is a fatty substance that insulates the axons and vastly increases the speed of transmission of electrical impulses from neuron to neuron. Whereas sensory and motor brain regions become fully myelinated in the first few years of life, axons in some cortical regions, particularly the frontal and parietal lobes, continue to be myelinated well into adolescence in the human brain.

Recent MRI studies have confirmed these early cellular studies, demonstrating that some regions of the human brain continue to develop for several decades (see below).

2.-As an observer of brain and psychological development, where do you think is brain more plastic -and behavior moldable- and where less?

Until relatively recently, it was widely believed that the adult brain is incapable of change. There used to be a strong assumption that after the first few years of life the brain is equipped with all the cells it will ever have, and that adulthood represents a downward spiral of loss of brain cells and deterioration in learning, memory, and performance generally. But research is beginning to show that this view of the brain is too pessimistic: the adult brain is flexible, it can grow new cells and make new connections, at least in some regions. Although laying down new information becomes less efficient with age, there is no age limit for learning.

The brain’s plasticity — its capacity to adapt continually to changing circumstances — depends critically on how much it is used. Research on plasticity suggests that the brain is well set up for lifelong learning and adaptation to the environment, and that educational rehabilitation in adulthood is possible and well worth investment. On the other hand, the research also suggests that there is no biological necessity to rush and start formal teaching earlier and earlier. Rather, late starts might be reconsidered as perfectly in time with natural brain and cognitive development. Of course, the aging brain becomes less malleable and, as everyone getting older experiences, learning new things takes longer.

We discuss these issues at length in our book The Learning Brain (Blakemore & Frith, Blackwell, 2005).

3 .- Why is adolescence such a conflicting period?

Adolescence is a time of profound mental change, affecting education, social adaptation and character, as well as disposition to several forms of mental illness. Until recently, there was surprisingly little scientific evidence about cognitive and neural development during this important period of human life.

Recent research on the human brain has revealed that the prefrontal cortex continues to develop well beyond childhood. This brain region is responsible for “executive” functions, such as the ability to inhibit inappropriate behaviour and attend to two things at once, as well as social understanding and self awareness.

In my research, we use computerised tests to study the development during adolescence of social cognitive skills such as self awareness and understanding other people. This research has demonstrated improvement and changes in these social cognitive processes during adolescence.

In addition, we use brain imaging techniques (functional Magnetic Resonance Imaging or fMRI) to track changes in brain function during the teenage years. fMRI can be used to view the living human brain at work. When brain cells are active, they cause a local increase of blood flow, which can be detected by the MRI scanner. This remarkable technique allows us to look inside the human brain and discover how it processes information. My research looks at how the brain allows to us understand other people’s intentions and emotions and how the brain activity underlying these social cognitive abilities develops. A series of studies have demonstrated changes in activity in the brain regions involved in understanding other people between adolescence and adulthood.

The finding that emotional and social understanding, and brain activity during social-emotional processing, is still developing during adolescence has potential implications for social policy and education. The highly social, potentially emotionally-charged context of a classroom/school environment may interfere with the cognitive resources that can be devoted to academic learning. Adolescents should also get the opportunity to learn about their own brain development in school, as this may be useful and interesting for them.

The finding that decision-making, and social-emotional and brain development continues into adolescence has implications for the understanding of psychiatric disorders, many of which have their mean age of onset during the adolescent years (e.g. mood disorders, schizophrenia, addiction). Understanding adolescent brain development is likely to have far-reaching implications for the early identification and preventative treatment of at-risk groups of children and adolescents.

4.-What are the prospects and perils of the New brain sciences for education?

Knowledge of how the brain learns could, and will, have a great impact on education. Understanding the brain mechanisms that underlie learning and memory, and the effects of genetics, the environment, emotion and age on learning could transform educational strategies and enable us to design programs that optimise learning for people of all ages and of all needs. Only by understanding how the brain acquires and lays down information and skills will we be able to reach the limits of its capacity to learn. Neuroscience can now offer some understanding of how the brain learns new information and processes this information throughout life (see Blakemore & Frith, 2005).

Understanding the brain basis of social functioning and social development is crucial to the fostering of social competence inside and outside the classroom. Social functioning plays a role in shaping learning and academic performance (as well as vice versa), and thus understanding the neural basis of social behaviour can contribute to understanding the origins and process of schooling success and failure. It can also facilitate an understanding of how children with additional socio-emotional needs can be included in mainstream schools and how to reduce exclusion.

5.-What are you now working on?

The social brain in adolescence, cognitive control in adolescence, and social cognition in autism. My lab’s research is summarised here:

En español:

La plasticidad del cerebro – su capacidad de adaptarse continuamente a nuevas circunstancias – depende críticamente de cuánto se usa. La investigación sobre plasticidad sugiere que el cerebro está bien preparado para el aprendizaje permanente y la adaptación al medio, y que la rehabilitación educativa en la edad adulta es posible y una inversión que vale la pena. Por otro lado, la investigación también sugiere que no hay una necesidad biológica de precipitarse y empezar la enseñanza formal cada vez más temprano. Más bien, el comienzo tardío podría reconsiderarse como perfectamente en tiempo con el cerebro natural y el desarrollo cognitivo. Por supuesto, el cerebro envejecido se vuelve menos maleable y, como todo el mundo experimenta al envejecer, aprender nuevas cosas lleva más tiempo.