Neurodiversity. A phenomenon of thousands upon thousands of variations within the complex human brain. A concept representing variations in the beautiful, complex human brain. A sign of uniqueness following the evolution and growth of man. And like all such phenomena, there is sound research and science behind it. Let’s delve deeper into understanding the causes of these variations.

The science behind neurodivergence is multi-faceted. There are several factors that come into play concerning mental variations. These factors include genetics, infectious disease, immune disorders, environmental factors, and physical trauma. Every individual has had different experiences, so every brain is altered uniquely and distinctively – as the concept of neurodiversity explains.

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Inside the Brain

The most direct cause of mental conditions is the altered function of the brain. The brain itself consists of several specialized areas that control human behavior. A changed brain can result in changed behavior. Under performing or over performing areas of the brain can ultimately lead to a set of symptoms categorized as a mental disorder. 

An example of over activity of an area in the brain lies within treatment-resistant depression. This type of depression is caused by under activity in Brodmann area 25, which is home to most serotonin transporters. Another example lies within autism, where it is caused by excessive growth and under connectivity in certain brain regions.

What causes these effects in the brain? Let’s answer that question below.

Causes of Mental Disorders


As many of us have learned in biology classes, evolution occurs with a key component: variation in characteristics. Our ancestors passed down a multitude of differing traits throughout the course of history, providing us with the DNA we have today. 

The concept of mental illness isn’t new. In fact, the first recorded instances of mental illness come to us from over 6000 years ago in ancient Mesopotamia.  With this in mind, it’s important to realize that we all  have certain mental disorders that are passed down through generations. These include autism, attention deficit hyperactivity disorder (ADHD), bipolar disorder, major depression and schizophrenia. These conditions are commonly inherited through certain single genes and calcium channel genes. The genes 5-HTT, SLC6A4, and MAOA are seen as common factors in many mental disorders.

An example of inheritance of mental disorders is that children of parents with schizophrenia, bipolar disorder, and severe depressive behavior have a 1 in 3 chance of developing the disorder by adulthood. This is twice the probability of children with parents without such disorders. Overall, it can be concluded that genetics have a crucial role within neurodiversity.

Prenatal Trauma

Surprisingly enough, mental conditions can originate from an incident in pregnancy. Researchers have found many instances where this is true. For example, mothers who had influenza in pregnancy are three times more likely to give birth to a child with schizophrenia. Mothers with maternal iron deficiency during pregnancy are four times more likely to have a child with this condition. Undernourished mothers experienced a dramatic increase in the risk of having a child with future mania and depression. Additionally, exposure to infections, toxins, and maternal stress can even contribute to problems with depression, anxiety, autism, mood disorders, and attention-deficit hyperactivity disorder within the child.

Stress is a main factor in affecting the fetus. An unnecessary amount of stress responses can lead to inflammatory symptoms, causing long term harm to the fetus’ immune systems. The immune system strongly impacts brain function, so an alteration of the system could have consequences with the child’s future behavior. 

In general, inflammatory immune responses for mothers can lead to many issues. Behavioral differences in offspring related to autism were observed, as well as anxiety commonly seen in schizophrenia. Prenatal immune responses can also affect the reception of serotonin in children. They heighten the child’s immune response, causing their immune systems to overact and fight against the serotonin in the brain. This condition can result in depression later on in life.

Infections and Immune Responses

Inflammatory immune responses can occur in and affect people throughout their lives as well – not just mothers and their children. Severe infections leading to inflammation result in a 84% increased risk of developing a mental disorder diagnosis for the patient. This is accompanied with an increased 42% risk of the use of psychotropic medications.  Developing mental conditions from infectious diseases can happen to pretty much anyone – no matter the age and circumstances – if the disease is severe enough. As many may have concluded from the last few paragraphs, hyperactive immune responses largely impact brain function.

Physical Trauma

Unfortunately, it was recently discovered that almost 30% of the cases of mental illness are related to childhood trauma. Trauma itself is so common that around 70% of all adults in the US have experienced it from a major event in their lives. It is devastating to see the effects of something so tragic, as it sadly often results in mental disorders. Trauma inflicts extreme fear, panic, anxiety, stress, and depression. Those who experience it are susceptible to PTSD, anxiety disorders, and severe depression. 

However, all individuals have their separate reactions to trauma. Some may be affected more severely than others. Some may develop certain conditions while others won’t. Trauma is simply another instance where neurodiversity can emerge. 

Environmental Factors & Epigenetics

The study of epigenetics describes how the environment triggers gene expression

interactions between environment and biological predispositions. In other words, it studies how external factors can affect DNA. These factors can cause different conditions to appear in certain ways. Recent epigenetic research concludes that pollutants, pesticides, exercise, and even dietary choices can affect DNA, resulting in a change in the amount of people with mental conditions.

In 1985, there was a drastic observed change in the amount of people with mental conditions. For example, in a four- to five-year span, the rate of kids getting diagnosed with ASD (Autism Spectrum Disorder) went from 1:120 to 1:44. PTSD, depression, anxiety, stress, Alzheimer’s were increasing greatly as well. At the same time, big changes in common foods, pollutants, and exercise were made. There were more pesticides and pollutants, in addition to more sugary and processed food. High levels of exposure to such environmental factors generate stress and inflammation in the human body, which in turn causes hyperactivity in the immune system (again with the unfortunate immune responses). All of this ultimately results in affected brain function.


Conclusively, neurodiversity is affected by several factors, as mental conditions may arise from many situations. Whether it is trauma, disease, genetics, or the surrounding environment, many individuals are impacted by them, some more than others. Everyone has different, unique experiences, therefore making each and every one of us diverse. It is this foundation of diversity, of Neurodiversity, that our modern society needs to be built upon.