15.1: Biological Factors in Psychological Disorders- An Introduction
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- Describe how genetics and epigenetics contribute to psychological disorders.
Overview
This chapter discusses the biological perspective on psychological disorders, exploring how our brain structures, neural systems, and genetics contribute to the etiology of such disorders as schizophrenia, depression, bipolar, anxiety, and obsessive/compulsion.
Introduction
Although the term mental illness is often used when referring to disorders such as depression or anxiety, are these disorders really illnesses in the way that diabetes is an illness – that is a purely biological malfunction? Or are psychological disorders the product of something more intangible than a neurochemical imbalance or malfunctioning brain area, something such as a conditioned response to stress learned in childhood? The answer is both.
Within the field of psychology, it is generally acknowledged that psychological disorders develop out of a complex interaction of biological, social, and environmental factors. However, exactly how these factors interact with one another to produce a particular psychological disorder is still unclear. This is because diagnosing a psychological disorder is not like diagnosing other illnesses, such as diabetes or pneumonia.
When making a diagnosis of diabetes, a doctor may use a blood test to determine blood glucose levels. Similarly, to diagnose pneumonia, a doctor may order a chest x-ray to look for evidence of the infection. However, when it comes to diagnosing psychological disorders, there is currently no x-ray for depression or blood test for anxiety. Diagnosing psychological disorders is a more subjective process, based on the current symptoms an individual is experiencing.
The Diagnostic and Statistical Manual of Mental Disorders (DSM), 5th edition, (American Psychiatric Association, 2013) is the most widely accepted system used by clinicians and researchers for the classification of mental disorders, and outlines the diagnostic criteria for a specific mental disorder based on the symptoms an individual is experiencing. However, individuals suffering from the same disorder often display different symptoms while individuals suffering from different disorders may display many of the same symptoms, making the diagnosis of psychological disorders from outward symptoms alone, difficult.
The American Psychological Association periodically updates the Diagnostic and Statistical Manual of Mental Disorders - also called the DSM - so that it will accurately reflect our current understanding of the symptoms, etiology, and treatment of psychological disorders. The revisions to the DSM-5 were released in early 2022, in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR).
The remainder of this chapter focuses on the contributions of biological factors - such as brain structure abnormalities - to the development of psychological disorders.
Biology of Psychological Disorders
Research into the underlying biology of psychological disorders has primarily focused on the following three areas: (1) the structures of the brain, (2) the biochemistry of the brain, and (3) genetics and epigenetics.
Structures of the Brain
Research has shown that some psychological disorders appear to involve specific structures within the brain. For example, overactivity in an area of the brain known as Brodmann Area 25 (BA25), shown in Figure 17.1.1, is often present in individuals with clinical depression (also known as Major Depressive Disorder) (Mayberg et al., 2005). This area is part of a larger, limbic system structure known as the anterior cingulate cortex and interacts with other areas of the brain involved in mood, emotion and thinking. When this region is overactive, a person can experience an increased negative affect (e.g. sadness, anxiety) and decreased positive affect (e.g. happiness, joy) (Jumah & Dossani, 2021). We will explore the role of brain structures in more detail as we discuss specific disorders later in this chapter.
Check out the following article from Harvard Health for more on the brain and the biological factors that play a role in depressive disorders:
https://www.health.harvard.edu/mind-and-mood/what-causes-depression
Biochemistry of the Brain
In addition to the individual structures of the brain, researchers are also interested in what role our chemical communication systems – hormones and neurotransmitters –play in the development of psychological disorders.
The primary communication in the brain occurs between neurons (neurotransmission) using neurotransmitters at the junctions between neurons known as synapses. Many factors can influence synaptic communication in ways that may lead to maladaptive alterations or disruptions of this important form of communication. Such disruptions can then result in a display of symptoms associated with various psychological disorders.
For example, researchers believe that disruptions in the neurotransmitters, particularly dopamine, play an important role in schizophrenia (NIH, 2007). This link between dopamine and schizophrenia arose out of several observations including the benefit from drugs that blocked dopamine action. Later it was also observed that individuals addicted to cocaine or amphetamine sometimes showed symptoms very similar to those seen in cases of schizophrenia. Cocaine works by reducing the amount of monoamine neurotransmitters (dopamine, norepinephrine, epinephrine, and serotonin) that are taken back into the presynaptic neuron (Richards & Laurin, 2021), as shown in Figure 2. When this happens, more monoamine neurotransmitters, crucially dopamine, are available in the synapse for binding to the receptors on the postsynaptic neuron. We will discuss the dopamine theory of schizophrenia in more detail later in this chapter.
In addition to neurotransmitters, the brain also communicates via hormones, which are released by the endocrine system, and activate behaviors such as alertness or sleepiness, concentration, and reactions to stress. Elevated or depleted levels of certain hormones may be responsible for some of the symptoms seen in psychological disorders. For example, elevated levels of cortisol, a stress hormone, interfere with learning and memory as well as increase the risk of depression. High levels of cortisol have been shown to alter the function of serotonin receptors in the brain, leading to symptoms of depression (Qin et al., 2018).
Genetics and Epigenetics
Researchers have long recognized that many psychological disorders tend to run in families, suggesting a potential genetic factor. In family and twin studies, schizophrenia is significantly more likely to be present in an identical twin than a fraternal twin (Coon & Miller, 2007) and in individuals with a first-degree relative (e.g. mother or father) with schizophrenia.
Researchers have also linked several genetic variations, or mutations, to psychological disorders, including variations in two genes which code for the cellular machinery that helps regulate the flow of calcium into neurons (NIH, 2013). One of these calcium channel genes, CACNA1C, is known to affect the brain circuitry involved in emotion, thinking, attention and memory. Variations in this gene have been linked to disorders such as bipolar disorder, schizophrenia, and major depression.
Although individual genes, such as CACNA1C, have been linked to psychological disorders, most disorders are believed to be polygenic; that is linked to abnormalities in many genes, rather than just one. It is the complex interaction between multiple genes which may trigger a psychological disorder.
Furthermore, while researchers currently believe that genetic factors are implicated in all psychological disorders, they are not believed to be the sole cause. There are important gene-environment interactions, also known as epigenetic factors, unique to each individual (even identical twins) which may explain why some individuals with a genetic predisposition toward a certain disorder develop that disorder while others do not (e.g., why one identical twin develops schizophrenia, but the other does not).
References
American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). https://doi.org/10.1176/appi.books.9780890425596
Helen S. Mayberg, Andres M. Lozano, Valerie Voon, Heather E. McNeely, David Seminowicz, Clement Hamani, Jason M. Schwalb, and Sidney H. Kennedy (2005). Deep Brain Stimulation for Treatment-Resistant Depression. Neuron, 45(5), 651-660. https://doi.org/10.1016/j.neuron.2005.02.014
Jumah FR, Dossani RH. (2021) Neuroanatomy, Cingulate Cortex. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537077/
National Institutes of Health (US); Biological Sciences Curriculum Study. NIH Curriculum Supplement Series [Internet]. Bethesda (MD): National Institutes of Health (US); 2007. Information about Mental Illness and the Brain. Available from: https://www.ncbi.nlm.nih.gov/books/NBK20369/
Richards JR, Laurin EG. Cocaine. [Updated 2021 Jul 19]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK430769/
Qin, Dd., Rizak, J., Feng, Xl. et al. (2016). Prolonged secretion of cortisol as a possible mechanism underlying stress and depressive behavior. Sci Rep 6(30187). https://doi.org/10.1038/srep30187
Cross-Disorder Group of the Psychiatric Genomics Consortium (2013). Identification of risk loci with shared effects on five major psychiatric disorders: a genome-wide analysis. The Lancet, 381(9875), 1371-1379. https://doi.org/10.1016/S0140-6736(12)62129-1.
Attributions
Introduction: by Amy E. Coren, Ph.D., Pasadena City College and adapted by Alan Keys, Ph.D., Sacramento City College.
Biology of Psychological Disorders, Original material written by Amy E. Coren, Ph.D., Pasadena City College, Pasadena, CA and adapted by Alan Keys, Ph.D., Sacramento City College, Sacramento, CA.
Figure \(\PageIndex{1}\) Brodman Area 25. By Brodmann; Colured by was_a_bee; File:Brodmann_Cytoarchitectonics.PNG, Public Domain, via Wikimedia Commons.
Figure \(\PageIndex{2}\) Cocaine and DAT. RicHard-59, CC BY-SA 3.0, via Wikimedia Commons.