Research throughout the years continues to provide evidence that depressive disorders have some biological cause. While it does not explain every depressive case, it is safe to say that some individuals may at least have a predisposition to developing a depressive disorder. Among the biological factors are genetic factors, biochemical factors, and brain structure:
- Endocrine system
- Brain anatomy
If there is a genetic predisposition to developing depressive disorders, one would expect a higher rate of depression within families than that of the general population. Researchers support this with regards to depressive disorders as there is nearly a 30 percent increase in relatives diagnosed with depression, compared to 10 percent of the general population (Levinson & Nichols, 2014). Similarly, there is also an elevated prevalence among first-degree relatives for both bipolar I and bipolar II disorders as well.
Another way to study the genetic component of a disorder is via twin studies. One would expect identical twins to have a higher rate of the disorder as opposed to fraternal twins, as identical twins share the same genetic make-up whereas fraternal twins only share that of siblings, roughly 50%. A large-scale study found that there was nearly a 46% chance that if one identical twin was diagnosed with depression, that the other was as well. In contrast, the fraternal twin rate was only 20%. Despite the fraternal twin rate still being higher than that of a firs-degree relative, this study provided enough evidence that there is a strong genetic link in the development of depression (McGuffin et al., 1996).
Low activity levels of norepinephrine and serotonin, have long been documented as contributing factors to developing depressive disorders. This was actually discovered accidentally in the 1950s when MAOIs were given to tuberculosis patients, and miraculously, their depressive moods were also improved. Soon thereafter, medical providers found that medications used to treat high blood pressure by causing a reduction in norepinephrine also caused depression in their patients (Ayd, 1956).
While these initial findings were premature in the identification of how neurotransmitters affected the development of depressive features, they did provide insight as to what neurotransmitters were involved in this system. Researchers are still trying to determine exact pathways; however, it does appear that both norepinephrine and serotonin are involved in the development of symptoms, whether it be between the interaction between them, or their interaction with other neurotransmitters (Ding et al., 2014).
ENDOCRINE SYSTEM :
As you may know, the endocrine system is a collection of glands responsible for regulating hormones, metabolism, growth and development, sleep, and mood among other things. Some research has implicated hormones, particularly cortisol, a hormone released as a stress response, in the development of depression (Owens et al, 2014). Additionally, melatonin, a hormone released when it is dark outside to assist with the transition to sleep, may also be related to depressive symptoms, particularly during the winter months (seasonal affective disorder).
BRAIN ANATOMY :
More specifically, drastic changes in blood flow throughout the prefrontal cortex have been linked with depressive symptoms. Similarly, a smaller hippocampus, and consequently, the fewer number of neurons, have also been linked to depressive symptoms. Finally, heightened activity and blood flow in the amygdala, the brain area responsible for our fight or flight emotions, is also consistently found in individuals with depressive symptoms.
There are a number of structural abnormalities in individuals with bipolar disorder; however, what or why these structures are abnormal is yet to be determined. Researchers continue to focus on areas of basal ganglia and cerebellum, which appear to be much smaller in individuals with bipolar disorder as opposed to the general public. Additionally, there appears to be a decrease in brain activity in regions associated with regulating emotions, as well as an increase in brain activity among structures related to emotional responsiveness (Houenou et al., 2011). Additional research is still needed to determine exactly how each of these brain structures may be implicated in the development of the bipolar disorder.
The cognitive model, arguably the most conclusive model with regards to depressive disorders, focuses on the negative thoughts and perceptions of an individual. One theory often equated with the cognitive model of depression is learned helplessness. Coined by Martin Seligman (1975), learned helplessness was developed based on his laboratory experiment involving dogs. This study has been linked to humans through the research in attributional style (Nolen-Hoeksema, Girgus & Seligman, 1992).
- Maladaptive attitudes, or negative attitudes about one self, others, and the world around them, are often present in those with depressive symptoms.
- The cognitive triad also plays into the maladaptive attitudes in that the individual interprets these negative thoughts about their experiences, themselves, and their futures.
- Cognitive distortions, also known as errors in thinking, are a key component in Beck’s cognitive theory. Beck identified 15 errors in thinking that are most common in individuals with depression
- Finally, automatic thoughts, or the constant stream of negative thoughts, also leads to symptoms of depression as individuals begin to feel as though they are inadequate or helpless in a given situation. While some cognitions are manipulated and interpreted in a negative view, Beck stated that there are another set of negative thoughts that occur automatically.
The behavioral model explains depression as a result of a change in the number of rewards and punishments one receives throughout their life. This change can come from work, intimate relationships, family, or even the environment in general. Among the most influential in the field of depression is Peter Lewinsohn. He stated depression occurred in most people due to the reduced positive rewards in their life. •Because they were not being positively rewarded, their constructive behaviors occurred more infrequently until they stop engaging in the behavior completely (Lewinsohn et al., 1990; 1984). An example of this is a student who continues to receive bad grades on their exam despite studying for hours. Over time, the individual will reduce the amount of time they are studying, thus continuing to earn poor grades.
In the sociocultural theory, the role of family and one’s social environment play a strong role in the development of depressive disorders. There are two sociocultural views- the family-social perspective and the multi-cultural perspective.
FAMILY-SOCIAL PERSPECTIVE :
Similar to that of the behavioral theory, the family-social perspective of depression suggests that depression is related to the unavailability of social support. This is often supported by research studies that show separated and divorced individuals are three times more likely to experience depressive symptoms than those that are married or even widowed (Schultz, 2007). While there are many factors that lead a couple to separate or even end their marriage, some relationships end due to a spouse’s mental health issues, particularly depressive symptoms. Depressive symptoms have been positively related to increased interpersonal conflicts, reduced communication, and intimacy issues, all of which are often reported in causal factors leading to a divorce (Najman et al., 2014).
MULTI-CULTURAL PERSPECTIVE :
Common depressive symptoms such as feeling sad, lack of energy, anhedonia, difficulty concentrating, and thoughts of suicide are hallmarks in most societies, other symptoms may be more specific to one’s nationality. More specifically, individuals from non-Western countries (China and other Asian countries) often focus on the physical symptoms of depression- tiredness, weakness, sleep issues, and less of an emphasis on the cognitive symptoms. Individuals from Latino and Mediterranean cultures often experience problems with “nerves” and headaches as primary symptoms of depression (American Psychiatric Association, 2013).
GENDER DIFFERENCES :
There is a significant difference between gender and rates of depression, with women twice as likely to experience an episode of depression than men (Schuch et al., 2014). There are a few speculations of why there is such an imbalance in the rate of depression across genders.
- Artifact theory
- Hormone theory
- Life stress theory
- Gender roles theory
- Rumination theory