AP Psychology 5.4-5.5: Bipolar, Depressive, and Anxiety Disorders

Major depressive disorder (MDD)

A mental disorder involving a persistent depressive episode characterized by low mood and/or loss of interest or pleasure, along with other emotional, cognitive, behavioral, and physical symptoms that impair daily functioning.

What are the hallmark mood-related symptoms of major depressive disorder?

Pervasively depressed mood and anhedonia, meaning markedly reduced interest in or pleasure from normally enjoyable activities.

Anhedonia

A reduced ability to experience interest or pleasure in activities that were previously enjoyable; it is a core feature of depressive episodes.

What duration is generally required for a major depressive episode?

Symptoms must persist for at least two weeks and occur nearly every day, with clinically significant distress or impairment.

What cognitive symptoms can occur in major depressive disorder?

Poor concentration, impaired memory, hopelessness, pessimism, low self-esteem, excessive guilt, and recurrent thoughts of death or suicide.

What sleep changes are associated with major depressive disorder?

Depression may cause insomnia, including early-morning awakening, or hypersomnia. Disturbances in the sleep–wake cycle and daily variation in mood may also occur.

How can appetite and body weight change during depression?

Appetite and weight commonly decrease, but some people experience increased appetite and weight gain.

What physical symptoms may accompany major depressive disorder?

Fatigue, headaches, digestive complaints, unexplained pain, reduced energy, and psychomotor slowing or agitation may occur.

Psychomotor retardation versus psychomotor agitation

Psychomotor retardation involves slowed movements and speech, whereas psychomotor agitation involves observable restlessness or increased motor activity.

How may depression present differently in children and older adults?

Children may show irritability, loss of interest in school, and declining academic performance rather than overt sadness. Older adults may show recent cognitive problems, slowed movements, or less typical depressive symptoms.

What severe symptoms can occur in major depressive disorder?

Severe episodes may include psychotic symptoms such as delusions or hallucinations, as well as suicidal ideation, self-harm, self-neglect, or substantial risk of harm.

Why is suicide risk clinically important in major depressive disorder?

Depression can involve recurrent thoughts of death, suicidal ideation, or self-harm. Significant risk may require urgent intervention or hospitalization.

What is the typical age of onset for major depressive disorder?

The most common onset is during a person's twenties, although depression can occur at any age.

How variable is the course of major depressive disorder?

The course ranges from a single episode lasting months to recurrent episodes or a lifelong disorder. Future episodes are more likely in people with prior episodes, especially those with psychotic features.

What is the biopsychosocial model of depression?

It explains depression as arising from interacting biological, psychological, and social influences rather than from one single cause.

Diathesis–stress model

A model in which an underlying vulnerability, or diathesis, interacts with stressful life events to produce depression. Vulnerability may be genetic or shaped by learned psychological patterns.

How much of the variation in risk for major depressive disorder is estimated to be genetic?

Family and twin studies suggest that genetic factors account for approximately 40% of variation in risk. The remaining risk reflects environmental and psychological influences and their interactions with genes.

Why is major depressive disorder considered polygenic?

Risk is influenced by many genetic variants, each generally contributing a small effect, rather than by one gene with a simple inheritance pattern.

What environmental experiences increase the risk of major depressive disorder?

Adverse childhood experiences, abuse, neglect, family dysfunction, trauma, major life changes, unhappy relationships, social isolation, and possibly long-term air-pollution exposure can increase risk.

How does childhood trauma affect the course of depression?

It is associated with higher risk, greater severity, poorer treatment response, and longer-lasting illness, particularly when multiple forms of adversity occur.

What is the relationship between living alone and depression risk?

Living alone has been associated with increased depression risk, although this relationship may reflect interacting social, psychological, and health factors rather than a single direct cause.

Beck's cognitive triad

A pattern of negative automatic thoughts about the self, the world or environment, and the future that may contribute to depressive symptoms.

What medical conditions or substances can contribute to depressive symptoms?

Chronic or terminal illnesses, substance-use disorders, and some nutritional deficiencies may contribute. Depression can also be secondary to another medical condition or induced by medication.

What is medication-induced or iatrogenic depression?

Depressive symptoms caused or worsened by medical treatment. Reported medication classes include interferons, some beta blockers, isotretinoin, contraceptives, anticonvulsants, cardiac agents, and hormonal drugs.

Postpartum depression

A depressive disorder occurring after childbirth, associated in part with biological and hormonal changes surrounding pregnancy and delivery.

Seasonal affective disorder

A depressive pattern associated with seasonal changes, often involving reduced exposure to sunlight during certain times of year.

What are major pathophysiological systems implicated in depression?

Proposed mechanisms include monoaminergic neurotransmission, circadian rhythms, immune and inflammatory signaling, hypothalamic–pituitary–adrenal-axis function, and altered emotional brain circuits.

Monoamine theory of depression

The theory that inadequate signaling by monoamine neurotransmitters—especially serotonin, norepinephrine, and dopamine—contributes to depression. It is historically influential but does not fully explain the disorder.

Why is the simple monoamine-deficiency explanation insufficient?

Antidepressants can increase monoamine levels rapidly but often require weeks to improve symptoms; serotonin depletion does not reliably cause depression in healthy people, and some effective treatments do not primarily target monoamines.

What is the hypothalamic–pituitary–adrenal (HPA) axis's proposed role in depression?

Some depressed people show abnormal stress-hormone regulation, including altered cortisol responses and reduced dexamethasone suppression. These findings are not sufficiently sensitive or specific to diagnose depression.

How might inflammation and the immune system relate to depression?

Some people with MDD show increased pro-inflammatory cytokines and other immune abnormalities. Inflammation may affect neural signaling and behavior, but immune findings are variable and are not diagnostic by themselves.

What is the kynurenine pathway's proposed connection to depression?

Inflammatory activation may divert tryptophan metabolism toward kynurenine and quinolinic acid rather than serotonin production. Quinolinic acid can activate NMDA receptors, and higher levels have been associated with more severe depressive symptoms.

What is the gut–brain axis?

A two-way communication system between the gastrointestinal tract and the central nervous system. Differences in gut microbiota and gastrointestinal disorders have been associated with depression, but causation remains under investigation.

What brain-circuit changes are proposed in depression?

Models describe excessive activity in limbic, paralimbic, or salience regions that process negative stimuli, together with insufficient activity in prefrontal regulatory circuits.

How is major depressive disorder diagnosed?

Diagnosis is clinical: it uses the person's reported experiences, observations from family or friends when available, a history and mental-status examination, and evaluation of functional impairment. No laboratory test directly confirms MDD.

What does a mental-status examination assess in a depression evaluation?

It assesses current mood, thought content, cognition, behavior, hopelessness, pessimism, self-harm or suicide risk, and the presence of psychotic symptoms.

Why might laboratory tests be ordered when evaluating suspected depression?

They help rule out medical conditions that can mimic or worsen depressive symptoms, such as hypothyroidism, metabolic disturbances, anemia, infection, chronic disease, or medication effects.

What is the role of depression rating scales?

Scales such as the Hamilton Rating Scale for Depression and Beck Depression Inventory estimate symptom severity over a defined period. They support assessment and monitoring but do not independently establish the diagnosis.

How do DSM and ICD systems classify depressive disorders?

The DSM-5-TR and ICD-11 provide standardized diagnostic criteria. ICD-11 distinguishes single-episode depressive disorder from recurrent depressive disorder and allows specifiers for severity, psychosis, and remission.

What distinguishes single-episode from recurrent depressive disorder?

Single-episode disorder involves no prior depressive episodes, whereas recurrent disorder involves a history of previous episodes. A history of mania would shift consideration toward bipolar disorder.

What is the importance of differential diagnosis in depression?

Conditions such as bipolar disorder, ADHD, autism-spectrum disorder, dementia, substance effects, medical illness, and ordinary sadness can resemble or coexist with depression and must be distinguished during evaluation.

Why must bipolar disorder be considered before treating depression?

A depressive presentation may be part of bipolar disorder. Identifying past mania or hypomania changes diagnosis and treatment planning because treatment for unipolar depression may be inappropriate alone.

How can major depressive disorder affect functioning?

It can impair relationships, work, education, sleep, eating, physical health, concentration, and general self-care. It is a major contributor to years lived with disability.

What are the principal evidence-based treatments for major depressive disorder?

Common treatments include psychotherapy and antidepressant medication. Depending on severity, response, and risk, options may also include exercise, electroconvulsive therapy, and transcranial magnetic stimulation.

Psychotherapy for major depressive disorder

Structured talking therapies help modify unhelpful thoughts and behaviors, improve coping, and address interpersonal or environmental contributors. They are a major first-line treatment option.

What is electroconvulsive therapy (ECT) used for in depression?

ECT is a biological treatment that can be particularly useful for severe, psychotic, treatment-resistant, or urgently life-threatening depression.

What is transcranial magnetic stimulation (TMS)?

TMS uses magnetic stimulation to influence brain regions involved in mood regulation. It is a noninvasive treatment option, often considered when depression has not responded adequately to initial treatments.

Why might hospitalization be necessary for someone with major depressive disorder?

Hospital care may be needed when there is substantial suicide or violence risk, severe self-neglect, psychosis, or inability to maintain basic safety. In some circumstances, hospitalization may be involuntary.

How does depression differ from ordinary sadness?

Sadness is a common emotional response that may be proportionate to circumstances and usually resolves over time. MDD is more pervasive or persistent, includes characteristic symptoms such as anhedonia, and causes significant impairment.

How can cultural and social factors affect depression diagnosis?

People may express distress primarily through physical symptoms, and stigma or pressure to conceal symptoms can reduce help-seeking. These factors can lead to underrecognition, especially in primary care and older adults.