What Are Neurodevelopmental Disorders?

The term ‘neurodevelopment disorder’ is commonly used, and there usually isn’t much context given about what a neurodevelopmental disorder is. This article hopes to give you a better understanding of the condition by giving you understandable and sensitive information gathered from trusted scientific sources.

A neurodevelopmental disorder is when a person’s brain development is atypical, affecting how the brain works.¹ This change in brain development can cause difficulties with acquiring and understanding information and negatively impact communication, motor skills, and behaviour.² Common neurodevelopmental disorders include autism spectrum disorder (ASD) and attention deficit and hyperactivity disorder (ADHD).³

This article will help give you an understanding of what typical neurodevelopment looks like, what factors affect neurodevelopment, various neurodevelopmental disorders, and some of the areas of a person’s life that can be affected by atypical brain development. 

Looking after somebody can be difficult, we acknowledge that. There is so much to look out for, making it understandable that this article, on top of all the other information that you are taking in, can seem daunting and maybe even overwhelming. However, it must be mentioned that despite any neurodevelopmental difficulties a person may face, creating and maintaining a home environment that is safe, supportive, and stimulating, along with parental responsiveness (being accepting, nurturing, supportive, sensitive, and warm), have been seen as very influential over a person’s development in life.

Typical neurodevelopment

As you have probably heard hundreds of times before, the human brain is incredibly complex. It develops from the tip of a 3-millimetre structure known as the neural tube (which the foetus develops in weeks 3-4 of pregnancy). Later, with the neural tube, the spinal cord will develop into a structure with over 100 billion neurons (brain cells).^4,5

Brain development can be broken up into 5 steps, beginning roughly 5 weeks after a foetus is conceived, with more than one of these steps potentially happening at the same time.

Step 1: A lot of brain cells are produced

In the beginning, many brain cells are produced, but these cells are not yet adapted to the environment of the brain, making them all very similar at this stage. The cells reproduce in a set area of the brain known as the ventricular zone. Here, cells divide in two, with this division happening in cycles – each division cycle doubling the cells in the brain. 

A small change in the timing, duration, or number of cycles can have a major impact on the brain, possibly causing a certain layer of the brain to become underdeveloped.⁴ 

Step 2: The brain cells (neurons) migrate to where they need to be

The brain develops from the inside outwards, with the cells able to travel as far as the outer layer of the brain (known as the cerebral cortex) from their start point – the ventricular zone. Each brain cell has a set path and destination, with different cells involved in these pathways to guide the neurons to their destination. 

Since the brain develops from the inner to the outer layers, neuron cells must move past other neurons that have already found their place in the brain. It is thought that the stationary neurons share information with the moving neurons to help with the next development stage of the brain. Issues in this process can lead to brain cells arriving at the wrong destination.⁴

Step 3: Forming regions in the brain

After a cell has migrated, it tends to group up with other similar cells in an organised way. Cells of the same type recognise each other and clump together to form an area of the brain, sometimes even arranging themselves to face the same direction. This grouping of cells into particular areas of the brain decides how each part of the brain forms and the function of that area. 

As more cells add themselves to an already crowded area of the brain (increasing its surface area), the outer layer of the brain will begin to scrunch up into folds and creases to accommodate a larger number of cells. While there, the cells also finish adapting themselves to their new role in that specific area of the brain.⁴

Step 4: Cells in the brain forming connections with each other

While the regions of the brain are developing, cells in these regions are forming connections to each other (called synapses) that allow them to send signals and information.⁶ 

Synapses can form between any of the following parts of the neuron: 

• Axons – which act as wires, allowing to send signals over large distances
• Dendrites – acting as input ports in a device, receiving information sent by other brain cells 
• Soma (cell body) – the core of the cell, receiving and sending the signals and integrating the information to control the neuron’s functions. 

Signals in these connections between the brain cells are sent through neurotransmitters – chemical signals, for example, dopamine, which allow the brain to communicate (or, instead, electrical signals in the case of connections between cell bodies). 

Many different signalling molecules are used to direct this growth of connections between the neurons. It’s done by cells by giving directions to other cells on where to form connections or by giving nutrients to another cell. It is because of the way these connections “connect everything with everything” that the brain is so effective at integrating information.

Step 5: Removing extra cells and connections plus fixing errors

Far too many synapses and a few too many neurons are formed during early brain development. The brain removes many of these connections and a few neurons to work at its best. The connections in each person’s brain are unique and affected by many experiences and exposures. It is theorised a person may have too many synapses and neurons at birth so that the body can choose which are most useful to keep.

Neurons and synapses must compete for nutrients. The following are thought to help decide if a connection or neuron stays: 

• A cell targeted by the connection gives nourishment 
• The targeted cell’s outer surface has enough space to maintain a connection
• An active brain cell communicates back to its cell body to increase its growth.

The process of modifying connections also removes cells that were misplaced in the brain due to misreading directions given during the migration process. If these misplaced cells are not removed, they can contribute to certain developmental disorders of the brain.⁴ 

What happens next?

After 18 months, no new neurons are added, and the cells have roughly finished grouping together in specific regions. The removal of excess connections in the brain is a process that happens for years after the first 5 weeks of gestation (pregnancy).⁴ The brain continues to develop until a person is in their late 20s.

Factors affecting neurodevelopment

The widespread changes in the brain’s structure that lead to neurodevelopmental disorders are caused by the brain’s development process being interrupted by factors affecting the foetus in the womb or an individual in early life. There are usually multiple causes of a neurodevelopmental disorder rather than one specific reason.^8,9 These factors include:

• Genetics – certain genes have been associated with some neurodevelopmental disorders. However, genetic factors alone do not explain a direct cause of ‘most’ neurodevelopmental disorders.⁹
• Toxicities – many toxins, including toxins in the environment such as lead, methylmercury, and PCBs (polychlorinated biphenyls) can contribute to the risk of neurodevelopmental disorders arising. Foetuses are particularly vulnerable due to a lack of protection from the blood-brain barrier (a barrier that stops harmful substances from getting into the blood that reaches the brain). Children are also more sensitive than adults due to children having worse detoxifying mechanisms and worse immune systems. Substances such as illicit drugs and alcohol can also negatively impact brain development.^9-12
• Environmental – for a foetus, the mother can be considered as their external ‘environment’, so alcohol, tobacco and illicit drug use during pregnancy are risks for neurodevelopmental disorders. There are also certain contaminants in the environment (like those mentioned under toxicities) that impact neurodevelopment.⁹
• Social – Maternal stress, the composition of the family (whether there are two parents and if those parents are living together or separated), and even the child’s order of birth compared to their siblings.^13,14
• Psychological – maternal psychological well-being during pregnancy has been shown to impact the neurodevelopment of the child. Additionally, socioeconomic status and early life stress experienced by the child were considered factors affecting the brain’s development.^9,14-15
• Educational – the brain is both physically and chemically changed during learning, allowing for new connections to form. For this reason, making a good school environment, having quality early childhood education, and increasing parental involvement is beneficial for neurodevelopment.¹⁶
• If the baby was born preterm or with a low birthweight.⁹
• Sometimes, some connections even form accidentally.⁴

There are also factors related to the foetus itself which affect its brain development (through synaptic formation), such as;

• The foetus moving (kicking, turning, and thumb sucking)
• The foetus’ senses picking up on its’ environment including; temperature, pressure, and what the foetus hears (although the foetus’ brain isn’t able to associate the sound with anything yet).⁴

Types of neurodevelopmental disorders

Often, a person will suffer from multiple neurodevelopmental disorders at once.¹⁷ Some of the examples include:

• Attention deficit hyperactivity disorder (ADHD) 
  Individuals with this condition may find it difficult paying attention, controlling impulsive behaviour, and/or be overly active. ADHD is one of the most common childhood neurodevelopmental disorders.
  For more information: https://adhduk.co.uk/about-adhd/
• Autism spectrum disorder (ASD) 
  A person with ASD may communicate, interact, learn, and behave in ways different to those without the condition, along with often having repetitive behaviours or interests. 1 out of every 100 children born in the world are thought to have autism.
  For more information: https://www.autism.org.uk/advice-and-guidance/what-is-autism
• Learning disabilities 
  Those with learning disabilities can have difficulties with understanding language (spoken or written), mathematics, coordination, or with attention.
  For more information: www.mencap.org.uk/learning-disability-explained/what-learning-disability 
• Intellectual disability 
  An intellectual disability is when an individual has limits to their ability to learn and function when compared to an expected level in day-to-day life.
  For more information: www.psychiatry.org/patients-families/intellectual-disability/what-is-intellectual-disability 
• Conduct disorders 
  These disorders involve behaviours that affect children’s development and interfere with their normal lives. These behaviours include ongoing aggression towards other people and serious violations of and social norms.
  For more information: www.nationwidechildrens.org/conditions/conduct-disorders 
• Cerebral palsy
  A motor disability that causes weakness in or issues with using muscles, which can lead to issues with movement and posture.
  For more information: www.nhs.uk/conditions/cerebral-palsy/ 
• Vision impairments
  Severe vision impairments commonly have an association with other kinds of impairments, with vision impairment being at an increased rate in children with neurodevelopmental issues. It is recommended that children with neurodevelopmental issues have routine vision checks.¹⁸ For more information: www.nhs.uk/conditions/vision-loss/ 
• Hearing impairments
  Hearing impairments can cause difficulties with communication, language development, social isolation, loneliness, and frustration.
  For more information: www.nhs.uk/conditions/hearing-loss/ 
• Schizophrenia
  Those with schizophrenia may have difficulties distinguishing their thoughts and ideas from reality, with symptoms including hallucinations, delusions, muddled thoughts and speech, and the person feeling disconnected from their feelings or emotions.¹⁹
  For more information: www.nhs.uk/mental-health/conditions/schizophrenia/overview/ 
• Bipolar disorder
  A condition that affects an individual’s mood which can change from one extreme to another. The person who experiences bipolar disorder can experience episodes of depression and mania (feeling high moods and being overactive).¹⁹
  For more information: www.mind.org.uk/information-support/types-of-mental-health-problems/bipolar-disorder/about-bipolar-disorder/ 

Areas of life typically impacted by neurodevelopmental disorders 

The symptoms and behaviours caused by neurodevelopmental disorders and the impact that a condition has on an individual are dependent on its severity. The condition is likely to alter as a child grows - however, some disabilities are permanent.⁹ 

Areas that can be affected in an individual’s life include

• Language and speech
• Motor skills and function
• Behaviour
• Memory
• Learning
• Mental health
  It is not known for certain whether having neurodevelopmental disorders makes a person more prone to poor mental health. ²⁰ However, additional mental health problems are much more common in people with certain neurodevelopmental conditions. For example, high levels of anxiety arise from difficulties with communication or being overwhelmed.

Summary 

Neurodevelopmental disorders are conditions forming as a result of atypical brain development, resulting in problems with cognition, communication, motor skills and behaviours of an affected individual. Typical neurodevelopment takes place from early pregnancy and early childhood and continues till the early 20s. During that time, the brain develops in five key stages: production of cells, their migration, formation of brain regions, making connections and refining them. 

Multiple factors can alter the brain’s development, including genetics, environment, social, psychological and educational aspects of life. Atypical neurodevelopment may lead to widely known ADHD and autism spectrum disorder, as well as learning difficulties, impairment of sensory systems, schizophrenia and bipolar disorder. Each of those conditions comes with particular difficulties of different severity that can negatively affect an individual’s well-being. It’s important to note that as the presentation of the disease may change over time, some of the disabilities may be permanent.