Exploring behavioural development
Studies on the plasticity of behavioural development across ages could help better explain and even enhance human behavioural development. Behavioural development is best studied using a multidisciplinary, integrated approach in large-scale longitudinal studies. Adhering to scientific criteria and collaboration across studies can improve research efforts.
Behavioural development is an essential survival tool, whereby experience modifies the way we interact with our environment. This process begins in the womb and continues into old age1 (Fig. 1), Behavioural development is influenced by multiple environmental factors, from parents’ educational aspirations to state retirement policies. Over a lifetime, brain biology, behaviour and environment interact and influence each other to determine an individual’s overall development.
It is helpful to distinguish three types of mechanism that jointly determine behavioural development: age-related brain mechanisms that are especially pronounced during early development (maturation); degenerative processes that become more important later (senescence); and learning throughout life, induced by behaviour–environment interactions. Maturation and learning work together in early life to shape neuronal connections2, and at least some relevant mechanisms subsist into old age. Senescence-related changes in brain chemistry begin in early adulthood. All three interact and influence each other throughout life, and all are dependent on and influenced by physical and social environments.
The study of behavioural development faces three integrative tasks. First is the need to relate research across functional domains. Often, domains such as sensation, perception or motor performance, as well as various aspects of cognition, volition and motivation, are studied in isolation, even though their functioning and evolution are highly interdependent.
Second is the need to discriminate between processes operating at different timescales, and to understand the mechanisms that link transient short-term variations to more permanent long-term change3. Establishing these links will help identify mechanisms that are short-term precursors of long-term development.
Third, to arrive at mechanistic explanations of behavioural change, behaviour must be connected with neuronal organization and genetic composition. These connections are rarely one-to-one, as many behaviours have multiple underlying implementations within the brain. Therefore, as an individual develops, changes in behavioural repertoires are likely to be associated with ongoing changes in multiple brain–behaviour mappings. Some of these re-mapping gradients might be relatively universal and age-graded, whereas others might be more variable, reflecting genetic differences, person-specific learning histories, the path-dependent nature of developmental dynamics or a combination of the three.
INTEGRATION IN ACTION
Considering these concepts and challenges, studies on behavioural development should meet one or more of three criteria: focus on how individuals develop in the context of their physical and social environments, explore and track the ability of individuals to change their behaviour (behavioural plasticity) in response to new demands from the environment4,5 (Fig. 2), and integrate neuronal and psychological evidence across timescales, while taking into account functions of behaviour. A growing number of recent studies fulfil one or more of these criteria.
For example, the interactive effects of learning and senescence on the ability to process multiple sensory inputs was investigated by Lövdén6. His team asked adults aged 20–30 or 60–70 years to find their way to a bistro in a museum, represented as a virtual reality projection on a screen in front of a treadmill. Walking demands affected navigation performance only in the older adults, implying that sensori-motor behaviour is more attention-demanding in this population.
In a separate study, a team led by Brehmer tracked how learning and maturation affect episodic memory — remembering specific events — and how this changes and develops with age7. Four groups, aged 9–10, 11–12, 20–25 and 65–78 years, were taught a memory technique. Children and older adults were at a similar level at baseline and immediately after instruction, but the children improved more with practice and reached higher levels than the older adults. Retested after 11-months, all children had improved, but the older adults’ performance had declined. Re-instruction had little effect on the children’s performance but improved that of the older adults. This suggests that learning and maturation forge a strong alliance in middle childhood, which enhances episodic memory plasticity.
Other studies have adopted a more integrated approach, for example by studying how birth cohorts differ in the way they age, investigating how short-term fluctuations in behaviour predict long-term changes and exploring whether the effects of genes on individual differences in cognition differ by age.
LOOKING AHEAD: THE MULTIDISCIPLINARY APPROACH
Taking an integrated, multidisciplinary approach to the study of behavioural development over an individual’s lifetime requires large-scale group studies that bridge the gap between natural and social sciences, combining experimental intervention with longitudinal observation. Critical design features include the following: looking at whole households instead of single individuals, which allows the recruitment of more people, including children yet to be born8,9; including a sufficient number of households, which enhances heterogeneity and population estimates; including a disproportionately large number of identical and non- identical twins and other sibling relations, which allows the study of genetic and environmental mechanisms; including more old people, which ensures that causes, correlates and consequences of longer lives can be studied; using state-of-the-art technology, which helps describe physical and social aspects of environments; following different birth cohorts, which allows the analysis of factors that have changed over historical time; and studying several countries at once, which allows the identification of trends across and within cultures.
The more of these characteristics that are included in a study, the more likely it is to produce advances in knowledge, which might help influence, and even improve, behavioural development.
Improving understanding of behavioural development will need a sustained, collaborative effort across disciplines10. Researchers must integrate evidence on functions of behaviour across timescales and types of analysis, and overcome the divide between the natural and social sciences. Combining experimental and longitudinal research designs in large- scale studies will improve understanding of behavioural development and potentially allow us to influence its course.
There are massive benefits of taking an integrated, multi-disciplinary approach to the study of behavioural development over an individual’s lifetime. This requires establishing large-scale group studies that combine the natural and social sciences, and experimental intervention and longitudinal observation. Several Max Planck Institutes have initiated, and are participating in, such studies. Examples include the Berlin Aging Studies, which are co-ordinated by the Max Planck Institute for Human Development.