Theories of Depression

Depression is one of the most common mental health disorders. In 2017, over 19% of the UK population showed symptoms of either depression or anxiety. Globally, 280 million are reported to have depression.¹ Depression can be debilitating. Due to its prevalence in society, identifying the causes of depression has been of interest to psychologists for decades. We will discuss the two leading theories of depression that guide contemporary treatment approaches.

Depression is one of the most common mental health disorders, freepik.com

What is depression?

How can we tell when the low mood becomes clinical depression? To diagnose depression, clinicians use diagnostic manuals like the International Classification of Diseases 10 (ICD 10) and the Diagnostic and Statistical Manual of Mental Disorders (DSM). Let's examine the criteria outlined for a depression diagnosis.

The characteristics of clinical depression

The International Classification of Diseases lists ten symptoms of depression based on which an individual is diagnosed. If a patient has experienced at least four of these symptoms in the past two weeks, they can be diagnosed with mild depression; experience of five to six suggests moderate depression and more than seven symptoms point to severe depression.

The frequency of symptoms is also essential for making diagnoses. Here is an overview of depressive symptoms from the ICD.

• Depressed mood for most of the day and almost every day
• Decreased energy and fatigue
• Loss of interest or pleasure in activities that are usually enjoyable
• Changes in appetite and weight
• Changes in sleep patterns or sleep disturbance (e.g. sleeping more or less than usual)
• Decrease in confidence and self-esteem
• Feelings of guilt, excessive self-criticism
• Thoughts of death and suicide
• Decreased ability to concentrate or think
• Excessive agitation or retardation (slower movements)

Key statistics on depression

• The reported prevalence of depression varies. It is estimated that 4.5% of the adult population in the UK suffers from depression.
  • However, this number is likely larger. In 2017, 17% of the adult population was prescribed antidepressants.
• Statistics also show differences in prevalence depending on gender (higher rates of depression tend to be reported for women) and age (higher rates of depression have been reported in groups of older adults).
• Differences have also been reported based on ethnicity. Black women are more at risk of experiencing depression than White women.

• Recovery from depression is common. According to NHS 2017-18 statistics, over 50% of treatments for depression end with the patient's recovery.

What are the psychological theories of depression?

Traditionally, the biological theory of depression argues that biological dysfunction in the body causes depression. Often you can hear that mental illness results from a 'chemical imbalance' in the brain.

However, there's little evidence that biological factors cause depression. The psychological theory of depression looks beyond biological correlates and focuses on cognitive and behavioural processes in depression.

Both approaches have informed treatment approaches, the biological theory has led to the development of antidepressant medications, and the psychological theory has informed therapeutic treatment approaches like cognitive behavioural therapy.

Psychological theories of depression

Psychological theories of depression focus on cognition and behaviour in regulating mood. This approach stresses the influence of our past experiences (nurture) in shaping our thought patterns that can result in depressive symptoms.

Past experiences can cause people to develop negative schemas – biased patterns of thinking about ourselves, others and the world around us, maintaining psychological distress. The psychological theories of depression are supported by the effectiveness of therapies like CBT, which aim to challenge negative schemas in treating depressive symptoms.

Negative schemas maintain depressive symptoms, freepik.com

Biological theories of depression

Biological theories of depression identify biological factors like genes, brain structure, and the function of neurotransmitters and hormones as the cause of depression. Biological theories stress the influence of nature in causing depression.

Biological theories focus on physical factors that correlate with depression, flaticon.com

Depletion of neurotransmitters: the monoamine theory of depression

The monoamine theory of depression predicts that depression results from reduced levels of monoamines like serotonin. Serotonin is a neurotransmitter. It functions as a messenger in the brain and is associated with regulating functions that are affected in depressed individuals, like mood and sleep.

Based on this theory, antidepressants (SSRIs) have been developed and shown to reduce depressive symptoms in some patients. A significant criticism of antidepressants is that their effectiveness is not much higher than a placebo, and they can cause serious side effects in some patients. However, antidepressant treatment can be more accessible than therapy for many patients.

Behavioural theory of depression

Behavioural theory of depression proposes that depressive symptoms are perpetuated by avoidance behaviour. Depressed individuals will often avoid potentially rewarding activities and become withdrawn, making their symptoms worse. One way this approach influences treatment is by informing behavioural interventions like Behavioural Activation, which encourages clients to schedule pleasant activities. Rather than focusing on changing one's thoughts and feelings, this approach attempts to increase the amount of positive experiences in one's daily life, which can in turn influence one's mental state.

The social rank theory of depression

Stevens and Price developed the social rank theory of depression. They proposed depression is an evolutionary adaptation; it allows individuals that fell to lower social ranks to accept their position.

Depressive symptoms prevent weaker individuals from engaging in conflicts that threaten their survival. Accepting one's lower position allows people to save resources instead of spending energy on conflicts and trying to regain a lost social rank, which could result in greater losses upon defeat.

While some literature findings align with this theory, it has been criticised for reductionism. In this case, depression is reduced to only evolutionary influences and situations when one loses social status. Still, we know depression is not limited to these situations and can result from a variety of life events.

Cognitive theory of depression

The ABC Model of clinical depression proposed by Ellis (1957) argues that distorted irrational beliefs (B) cause distress, forming as a response to an activating event (A). According to this model, depression is the consequence (C) of irrational beliefs.

Irrational beliefs can form automatically, and we may not even realise that we hold them. Irrational beliefs can include catastrophising, 'black and white' thinking and personalising.

Therapy helps individuals identify their irrational beliefs and challenges them so they can replace them with more adaptive ones.

Beck's negative cognitive triad

Aaron Beck (1967) proposed three main types of beliefs that maintain depressive symptoms. These include negative thoughts and beliefs about the self, the world, and the future. The three types of negative beliefs can be mutually reinforcing; for example, a negative belief about the world can strengthen a negative belief about the future.

Beck proposed different types of cognitive distortions commonly present in depressed individuals.

• Beck's cognitive distortions include minimisation of positive events, overgeneralising a single event, magnification of negative events, personalisation (feeling guilty for things you shouldn't), arbitrary inference (making conclusions that fit with negative beliefs without sufficient evidence) and selective abstraction (focusing only on negative elements of a situation and making conclusions based on that).

Seligman's negative attributions

According to Seligman, depression is an outcome of learned helplessness. Depressed individuals feel like no matter what they do, they cannot control the negative events in their life.

Learned helplessness is maintained by believing that we are the cause of the failure; we cannot change the cause, it's stable, and the failure is global. We will always fail in every situation. By challenging these thoughts, individuals can learn to feel more in control of their life and reduce the sense of learnt helplessness associated with depressive symptoms.

1. World Health Organization, Depression, 13 September 2021