Major Depressive Disorder

Major Depressive Disorder (MDD): Definition

around 2 weeks of low mood, loss of interest, fatigue, and cognitive issues.

MDD: Prevalence

5% adults per year, 10% lifetime prevelance.
More common in females.

MDD: Symptoms

Sadness, no enjoyment, low energy, sleep issues, worthlessness, suicide thoughts, memory problems

MDD: Beeper Study

Participants carried a beeper that went off randomly.

ppl with MDD→ rated they were NOT having happy moments

MDD: Movie Study

🎥 People with depression reacted sad to sad movies like The Notebook
😊 But only felt happy during half of the happy movies

MDD: Sleep Issues

Shifted body temp rhythm; temp drops earlier, rises earlier → altered sleep.

MDD: Genetic Link

~65% concordance in MZ twins, 17+ gene variants.
Sadness may be adaptive.

5-HTTLPR Gene x Environment

2 Short allele + many stressful events = ↑ risk of depression.

Monoamine Hypothesis

Depression = low dopamine (reward), serotonin (mood), norepinephrine (energy).

Antidepressants: Types & How They Work

• Tricyclics: Block reuptake of DA, 5-HT, NE

• SSRIs: Block serotonin reuptake

• SNRIs: Block serotonin & norepinephrine reuptake

• MAOIs: Block enzyme that breaks down monoamines

Antidepressants: Delay in Effect

Drugs act fast at synapse, but mood improves after weeks (BDNF buildup).

BDNF Theory

a protein that plays a key role in survival/growth of nerve cells in the CNS

→ ppl wit MDD have lower

Antidepressants vs Placebo

Effective for severe MDD. Less effective vs placebo in mild/moderate cases.

CBT (Cognitive-Behavioural Therapy)

🧠 Effective for all levels of depression
🔥 Increases brain metabolism like antidepressants
🔄 More likely to prevent relapse long-term

TMS (Transcranial Magnetic Stimulation)

Magnetic pulses deactivate brain areas. Non-invasive.

ECT (Electroconvulsive Therapy)

Induces seizure for severe MDD. Can cause memory loss (less if right hemisphere only)