Psychology 4 10

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Psychology 4.10 Biological View of Depression

When you leave, you will be able to discuss the biological view of depression including genetic factors.

The goals of today

According to the Biological perspective/model, what would the source of depression be?

Three types of studies seem to suggest that people inherit a predisposition to depression:

Family Pedigree studies Twin Studies Adoption studies

The Biological View of Depression (Genetic Factors)

Select people suffering from depression as probands (the person who is the focus of the study).

Then, they examine their relatives and see whether depression is present in their family.

To have some sort of conclusive support for a genetic link, the proband’s relatives should have a higher rate of depression than the average population.

Some researchers report as much as 20% of relatives (in family pedigree research) compared to 10% of the general population.

Family Pedigree Studies

Examined sets of twins and rates of depression.

200 pairs of twins were looked at.

When a MZ twin suffered from depression, there was a 46% chance that the other would also have a similar diagnosis.

When a DZ twin had depression, the other twin had a 20% chance of developing the disorder.

Twin Studies: Gershon and Nurnberger (1995)

One specific study looked at the families of adopted persons who had been hospitalized for depression in Denmark.

The biological parents of these adoptees had a much higher incidence of severe depression than the biological parents of the control group.

Adoption Studies

Briefly, explain the importance of twin studies and how they are used to study depression from the biological perspective.

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Neurotransmitters carry messages from one neuron to another.

Biochemical Factors

Responsible for various physical and cognitive activities: Sleep, pleasure, arousal, memory, muscle contraction, etc.

Neurotransmitters

Low activity of two neurotransmitters: norepinephrine and serotonin, have been strongly linked to depression.

This relationship is supported by two important pieces of evidence (discovered in the 1950’s):

1. Medical researchers discovered that reserpine and other medications for high blood pressure can cause depression. Why do you think that might be?

2. The conclusion that was drawn was that depression could be relieved by increasing the activity of norepinephrine or serotonin.

Neurotransmitters and Depression

These findings led some theorists to conclude that depression is a product of low norepinenphrine activity.

Neurotransmitters and Depression

Norepinephrine belongs to a class of chemicals called catecholamines.

This theory aims to connect the onset of depression to lowered levels of catecholamines.

Catecholamine Theory

Produced evidence that drugs which decrease the levels of noradrenaline can produce depression-like symptoms.

In one study, participants were given a drug called physostigmine.

Within minutes of receiving the drug, some felt intense feelings of self-loathing and suicidal thoughts.

Janowsky et al. (1972)

Likewise, some researchers identify a connection with serotonin.

Serotonin is belongs to the indoleamines, thus the indoleamine theory relates to lower levels of serotonin.

Indoleamine Theory

For years, it was believed that low activity of either of these neurotransmitters was capable of producing depression.

Researchers now believe that it is the interaction between the serotonin and norepinephrine systems.

Some research suggests that, in those suffering from depression, there is an overall imbalance of neurochemicals.

Another variation of this theory states that serotonin helps regulate other neurotransmitters. Low levels of serotonin activity disrupts the activity of the other neurotransmitters.

The Interaction of these biochemicals

The endocrine system may also play an important role the onset of depression.

What does the endocrine system produce?

The role of the endocrine system

People suffering from depression have been found to have abnormal levels of cortisol (hormone released during times of stress).

This seems consistent with the prevalence of depression in certain segments of society.

Why?

Cortisol levels and depression

Another hormone tied to depression is melatonin.

This hormone plays an important role in our circadian rhythms.

This hormone is released by the brain’s pineal gland only when dark.

In animals, it helps control hibernation, activity levels, and the reproductive cycle.

As nights grow longer, they release more and more melatonin. During the spring, melatonin secretions are on the decline.

Melatonin

For humans, heightened melatonin levels in winter seem to slow us down.

Some humans may be so sensitive to these heightened secretions, they find it impossible to carry on about their daily business.

Their slowdown takes the form of depression each winter. This pattern can result in seasonal affective disorder (SAD)

Melatonin and depression

Not surprisingly, SAD is less common in areas that receive more annual sunlight.

Some who are susceptible to melatonin decreases may be sensitive in the other direction as well: Manic episodes during the summer months may take place.

SAD

Some of most cited research as relied on analogue studies (depression-like symptoms are created in animals).

Until recent years, technology was limited. Biological studies of human depression had no way to measure brain activity directly: Neurotransmitters were estimated by measuring the activity of chemical by-products in the bloodstream, urine, and spinal fluid.

Measures of these substances may not directly reflect neurotransmitters.

Current technology has improved these limitations, but the progress is slow.

Limitations of the Biological explanation of depression