Psychological Disorders

Why This Is Tested

Psychological disorders sit squarely in MCAT content category 7A, which asks you to connect individual behavior and mental processes to their biological bases. Passages routinely present a symptom vignette and ask you to identify the disorder, its neurotransmitter correlate, or the treatment mechanism, so you need both the diagnostic distinctions and the underlying neurobiology.

Major Disorder Classes

Mood disorders. Major depressive disorder requires at least two weeks of depressed mood or anhedonia plus associated symptoms (sleep, appetite, energy, concentration changes, guilt, suicidal ideation). Persistent depressive disorder (dysthymia) is milder but lasts at least two years. Bipolar I requires at least one manic episode; bipolar II requires hypomania plus a major depressive episode. Cyclothymia is a chronic pattern of subthreshold highs and lows.

Psychotic disorders. Schizophrenia involves positive symptoms (hallucinations, delusions, disorganized speech and behavior) and negative symptoms (flat affect, avolition, alogia, social withdrawal), with disturbance lasting at least six months. Shorter courses are labeled brief psychotic disorder (under one month) or schizophreniform disorder (one to six months).

Anxiety disorders. Generalized anxiety disorder is excessive, free-floating worry more days than not for at least six months. Panic disorder features recurrent unexpected panic attacks plus persistent worry about future attacks. Specific phobias are intense irrational fears of particular objects or situations; social anxiety disorder centers on fear of negative evaluation by others.

OCD and trauma-related disorders. OCD pairs intrusive obsessions with anxiety-reducing compulsions, maintained by negative reinforcement. PTSD follows exposure to trauma and includes intrusion, avoidance, negative mood and cognition, and hyperarousal, lasting more than one month (shorter presentations are acute stress disorder).

Somatic and dissociative disorders. Somatic symptom disorder involves real, distressing physical symptoms with excessive health anxiety; illness anxiety disorder is preoccupation with disease despite minimal symptoms; conversion disorder produces neurological symptoms incompatible with organic disease. Dissociative disorders include dissociative identity disorder, dissociative amnesia (sometimes with fugue), and depersonalization/derealization disorder.

Personality disorder clusters. Cluster A (odd-eccentric): paranoid, schizoid, schizotypal. Cluster B (dramatic-erratic): antisocial, borderline, histrionic, narcissistic. Cluster C (anxious-fearful): avoidant, dependent, obsessive-compulsive.

Eating disorders. Anorexia nervosa requires significantly low body weight with intense fear of gaining weight; bulimia nervosa involves binge-purge cycles at roughly normal weight; binge-eating disorder involves bingeing without compensatory behavior.

Neurodevelopmental disorders. ADHD combines inattention and hyperactivity-impulsivity beginning before age 12 across multiple settings. Autism spectrum disorder involves deficits in social communication plus restricted, repetitive behaviors and interests, with early-developmental onset.

Biological Bases

• Monoamine hypothesis of depression: deficient serotonin, norepinephrine, and dopamine signaling; supported by the efficacy of SSRIs and SNRIs, which block presynaptic reuptake to raise synaptic levels.
• Dopamine hypothesis of schizophrenia: excess dopamine in the mesolimbic pathway drives positive symptoms (hence D2-blocking antipsychotics work), while reduced mesocortical dopamine contributes to negative and cognitive symptoms.
• Brain-region findings: reduced hippocampal volume in PTSD and chronic depression, linked to prolonged cortisol exposure; amygdala hyperactivity in anxiety and PTSD; prefrontal hypoactivity in depression and schizophrenia; basal ganglia and orbitofrontal circuits implicated in OCD.
• Treatment mechanisms: CBT restructures maladaptive thoughts and behaviors; exposure therapies (including systematic desensitization) extinguish conditioned fear via classical conditioning principles; stimulants for ADHD boost dopamine and norepinephrine transmission.

High-Yield Distinctions

• Bipolar I vs bipolar II: I requires full mania; II requires hypomania plus a major depressive episode, never full mania.
• Panic disorder vs GAD: panic disorder is discrete, intense attacks with anticipatory worry; GAD is chronic, diffuse worry lasting six months or more without necessarily any attacks.
• OCD vs OCPD: OCD has ego-dystonic obsessions and compulsions the person finds distressing; OCPD is an ego-syntonic personality style of perfectionism and control with no true obsessions.
• Schizophrenia vs schizoaffective disorder: schizoaffective requires a major mood episode plus at least two weeks of psychosis without mood symptoms; in schizophrenia, mood symptoms are brief or absent.
• Anorexia vs bulimia: anorexia requires significantly low body weight; bulimia patients are typically normal weight or above, even though both may involve purging and fear of weight gain.

Quick Self-Check

1. A patient has had hypomanic episodes and one major depressive episode but has never been hospitalized or psychotic. What is the diagnosis?
2. Which dopamine pathway explains why antipsychotics relieve hallucinations but not flat affect, and what is the pathway's abnormality in each symptom class?
3. What brain structure shows reduced volume in both PTSD and chronic depression, and what hormone is implicated in that change?