A Work in Progress: the Adolescent and Young Adult Brain: A briefing paper

Background

Until recently it was thought that the structure and make-up of the human brain was largely fixed from early childhood onwards. However, research 1  on post-mortem human brains and the use of Magnetic Resonance Imaging (MRI) scanning technology have demonstrated that the human brain does, in fact, undergo changes after this early sensitive period and develops throughout adolescence, young adulthood and even beyond.

Since neuroscience is confirming what mental health professionals working with this age group have long observed – that adolescence and young adulthood is a time of great potential for change and development – then policymakers need increasingly to focus on the opportunities for helping and influencing young adults that this crucial stage presents.

This paper summarises some recent findings from the field of neuroscience into adolescent and young adult brain development. It explores these findings, discusses the links between brain development and mental health, and concludes with some implications for mental health service policy for the 16-25 age group.

Areas of anatomy important for brain functioning

The human brain has a hierarchical organisation, from the lower, simpler areas (which function automatically and control our basic instincts: breathing, heart rate, and sense of territory, for example) to more complex functioning carried out by the limbic system (which controls our emotions, sexuality, sleep and immune system, and plays an important role in long-term memory), right up to the most complex operations carried out by the cerebral cortex (where capacities such as those for using language and abstract thinking are based).

Linkages between these different structures – essentially how parts of the brain ‘talk’ to each other – have a great influence on how people function.

Brain changes in adolescence and young adulthood

Just prior to puberty a wealth of grey matter is created and, as neurons develop, a layer of myelin is formed which greatly increases the speed of transmission of electrical impulses from neuron to neuron. A period of synaptic pruning then occurs throughout adolescence, a process not completed until the early 20s 2 , which is believed to be essential for the fine-tuning of functional networks of brain tissue, rendering the remaining synaptic circuits more efficient 3  . ‘The frontal cortex [where this development takes place] is essential for such functions as response inhibition, emotional regulation, analysing problems and planning. Many of these aptitudes continue to develop between adolescence and young adulthood’ 3  , whereas spatial awareness functioning and sensory functions (such as hearing and language processing) are largely mature by adolescence.

This pruning occurs on the ‘use it or lose it’ principle: this means that the activities undertaken by adolescents are critical to ensuring that circuits (or processing systems) which underpin adaptive, rather than maladaptive, functioning strengthen and grow. The frequency and intensity of experience determines the likelihood of particular synapses surviving this period of pruning.

Emotional functioning in adolescence

Research findings 4  suggest that there is a mismatch between emotional and cognitive regulatory modes in adolescence. The brain structures mediating emotional experience change rapidly at the onset of puberty, generating powerful emotional urges for sexual behaviour, independence and the formation of social bonds. However, the maturation of the frontal brain structures that underpin cognitive control lag behind by several years. This leaves the adolescent with powerful emotional responses to social stimuli that he or she cannot easily regulate, contextualise, create plans about or inhibit.

Equally, over-stimulation or under-stimulation of certain responses can lead to miscommunication between different areas of the brain 5 ; and the consequences of early stress include attenuated development of the left neocortex, hippocampus and amygdala 6 .

Psychological development

Neuroscientists use the term ‘executive function’ to refer to capacities such as controlling and coordinating our thoughts and behaviour, directing our attention, planning future tasks, inhibiting inappropriate behaviour, and keeping more than one thing in mind at once. All these are crucial for our ability to make sense of the life experiences we accumulate and to enable us to deepen our understanding of other people.

Studies have shown that the parietal and frontal cortices – brain regions which undergo continued development during adolescence 3  – are associated with making the distinction between first-person perspective and third-person perspective. ‘In order to reason about others and understand what they think, feel or believe, it is necessary to step into their ‘mental shoes’ and take their perspective. 3 ’ These findings may link with Peter Fonagy’s work on mentalisation 7 .

Studies show that our perspective-taking capacity dips during puberty 3  (our capacity for prospective memory – the ability to hold in mind an intention to carry out an action at a future time – also dips during this period). The elimination and reorganisation of prefrontal synaptic connections after puberty may explain why pubescent children have been shown in studies to be significantly poorer at responding to third-person perspective scenarios compared to first-person scenarios, whereas pre-pubescent children and young adults showed no difference in ability.

Too much, too young

Since self-restraint in the face of intense emotional experience is often less than robust at this age, it is hardly surprising that consumerism and the availability of alcohol and other drugs, for example, present great risks. Despite this, society continues to allow the adolescent a degree of agency never before afforded to people so inexperienced. Not only is the range of issues that young people are expected to make decisions about arguably wider than for previous generations, but the consequences of these decisions are less clearly articulated than ever before. The result is a tacit condoning of almost all aspirations, behaviours and lifestyles, leaving young people largely without guidance.

Because young people whose brains are still developing have relatively limited capacity to regulate their emotional responses, the predictable and usual social challenges they face can prove very difficult to surmount. The timing of the ‘normal’ maturation of prefrontal structures suggests that society’s expectations for young people’s planning, organisational and self-regulating capacities are often misplaced and may – when inflexibly imposed – create excessive stress for the adolescent brain. This stress has the potential for adverse (neurotoxic) effects on neuronal growth, functioning and organisation 8 .

Implications for service providers, commissioners and policymakers

The neuroscience research discussed in this paper demonstrates the great neuroplasticity of the brain throughout adolescence and beyond. The growth of capacities which one might, in common parlance, term emotional maturity are being shown to depend upon the physical development of the brain. The structure and provision of mental health services for young people up to the age of 25 needs to take into account the possibility of positive changes in the brain. If some young people do not have the capacity to benefit from services as they are presently structured, then it is incumbent upon service providers to offer different kinds of intervention, rather than deeming those young people unsuitable for treatment.

Although there are services that address the psychosocial needs of young people, such as Early Intervention in Psychosis Teams and drop-in services linked to Young People’s Information, Advice, Counselling and Support Services (YIACS), these resources are not universally available.

Commissioners need to consider the specific needs of this age group when planning and commissioning services 9  ;  failure to do so may contribute to the development of mental health service users being stuck in a cycle of hopelessness, unable to realise their full potential.

Conclusions

• Advancements in medical technology and research are rapidly expanding our knowledge and understanding of the structure and function of the developing human brain.
• A growing body of research is demonstrating that the adolescent brain is remarkably neuroplastic and undergoes specific and significant remodelling at many levels from the basic cellular architecture to the formation of new neural pathways and networks.
• The nature and location of these underlying neurobiological changes occur in parallel with, and help to explain, key shifts in psychological development observed during the adolescent period, particularly in the areas of executive functioning, emotional processing and social cognition.
• There is accumulating evidence that the neuroplasticity of the developing brain, particularly during adolescence, may be experience-dependent. In essence, the life experiences of each young person have a unique influence in the development of that individual’s brain and his/her current and future patterns of thinking, relating and behaving. 
• The current understanding of the adolescent brain is pointing to the existence of a developmental period in which there is both increased vulnerability to negative environmental experiences and enhanced receptivity to positive, including therapeutic, life experiences – both of which may carry long-term consequences for adult life.
• An evolving awareness of the complex changes in the developing adolescent brain carries major implications for the types of interventions and policies designed to improve outcomes for youth, particularly those already identified as being at increased risk.

Glossary

Adaptive functioning

A term which refers to an individual’s ability to modify behaviour to meet the demands of a changing environment.

Amygdala

A region at the centre of the brain, involved in the speedy and automatic processing of emotions, in particular fear and distress.

Cerebral cortex

Outermost layer(s) of brain tissue, particularly evolved in the human brain.

Executive functioning

High-level psychological processes of the frontal cortex, such as the ability to inhibit inappropriate behaviour, plan, select actions, hold information in mind and do several things at once.

Frontal cortex/lobe

The large region at the front of the brain just behind the forehead. This region is responsible for high-level cognitive processes, including planning, integrating information, controlling emotions and decision-making.

Grey matter

Masses of cell bodies in the brain that appear grey to the naked eye and as viewed on MRI scans.

Hippocampus

A seahorse-shaped structure deep in the brain’s temporal lobe and part of the limbic system, involved in storage and retrieval of memories, and spatial navigation.

Limbic system

A part of the brain (comprising structures such as the hippocampus, amygdala and thalamus) associated with basic needs and emotions, for example hunger, pain, pleasure, satisfaction and sex.

Magnetic Resonance Imaging (MRI)

A brain-imaging technique used for viewing the structure of the living brain.

Mentalisation

A term used to describe the unique human capacity that enables us to experience the subjective experience of our fellow humans 10 .

Myelin

A white, fat-like substance that forms a sheath around nerve fibres and which speeds up transmission of electrical impulses along neurons.

Neuron

Brain cell; the human brain contains 100 billion neurons.

Neuroplasticity

The ability of the brain to change physically in response to stimulus and activity.

Neurotoxicity

The propensity of a substance (including hormones and neurochemicals produced within the body) to cause harm to neuronal growth or functioning; stressful experiences are known to produce excessive amounts of neurotoxic substances.

Parietal cortex

A large region of cortex at the top and back of the brain on both sides, where spatial processing occurs.

Sensitive period

The period during which the brain is particularly likely to be affected by experience.

Synapse

Connection or specialised junction that allows information to be passed between neurons.

 

References

 1  Sowell, E. R., Thompson, P. M., Holmes, C. J., et al. (1999). In vivo evidence for post-adolescent brain maturation in frontal and striatal regions. Nature Neuroscience, 2 (10), pp. 859-861.

 2  The adolescent brain: beyond raging hormones. (2005). Harvard Mental Health Letter (July). www.health.harvard.edu/newsletters/Harvard_Mental_Health_Letter.htm

 3  Blakemore, S-J. & Choudhury, S. (In Press). Development of the adolescent brain: implications for executive function and social cognition.

 4  Monk, C. S., McClure, E. B., Nelson, E. E., et al. (2003). Adolescent immaturity in attention-related brain engagement to emotional facial expressions. NeuroImage, 20 (1), pp. 420-428.

 5  Perry, B. D., Pollard, R. A., Blakley, T. L., et al. (1995). Childhood trauma, the neurobiology of adaptation, and 'use-dependent' development of the brain: How 'states' become 'traits'. Infant Mental Health Journal, 16 (4), pp. 271-291.

 6  Teicher, M. H., Andersen, S. L., Polcari, A., et al. (2003). The neurobiological consequences of early stress and childhood maltreatment. Neuroscience & Biobehavioral Reviews, 27 (1-2), pp. 33-44.

 7  Fonagy, P., Gergley, G., Jurist, E. L., et al. (2002). Affect regulation, mentalization, and the development of the self. New York: Other Press.

 8  Schore, A. N. (2001). The effects of early relational trauma on right brain development, affect regulation and infant mental health. Infant Mental Health Journal 22 (1-2), pp. 201-269.

 9   YoungMinds, (In Press). SOS Commissioning Guidelines. See www.youngminds.org.uk/sos/outputs.php

 10  Hartley-Brewer, E. (2005). Perspectives on the causes of mental health problems in children and adolescents. London: YoungMinds. See www.youngminds.org.uk/sos/YM_MH_Causes_Symposium.pdf