Mood Research Background
Validated mood research has produced brief self-report measures spanning the nine DSM-5 Major Depressive Disorder symptom domains, with strong sensitivity and specificity demonstrated across primary-care and obstetric samples totalling thousands of participants. These measures show excellent test-retest reliability, are sensitive to treatment response, correlate with clinician-administered structured interviews and longer rating scales, and perform equivalently across age, gender, and ethnic groups. They are among the most widely deployed depression screening tools globally.
DSM-5 Major Depressive Disorder Criteria
MDD requires ≥5 of 9 symptoms present most days for ≥2 weeks, with at least one being depressed mood or anhedonia. Symptoms include: persistent depressed mood, anhedonia (diminished interest/pleasure), appetite change, sleep disturbance, psychomotor retardation/agitation, fatigue, feelings of worthlessness, concentration difficulty, and suicidal ideation.
The episode must cause clinically significant distress and represent change from baseline functioning. 12-month prevalence in the U S. is 7 1%, with females:males ratio of 1 7:1 (Kessler et al.
2012). Mean age of first episode is 32-35 years. Recurrence rate for those with one episode is 50%; for those with two episodes, 80% (Kupfer et al. 1992). Untreated episodes last 8-15 months (Solomon et al. 2000). Depression ranks as leading cause of disability globally (WHO 2017).
Monoamine Hypothesis
The monoamine hypothesis, first articulated by Schildkraut (1965) and refined by Lapin and Oxenkrug (1969), proposes that depression results from functional deficiency of serotonin, norepinephrine, and/or dopamine. Supporting evidence: SSRIs (selective serotonin reuptake inhibitors) block serotonin reuptake with 50-60% response rates, matching depression remission.
Norepinephrine-dopamine reuptake inhibitors (bupropion) are equally effective, supporting involvement of these monoamines. However, monoamine levels normalize within hours of SSRI administration, yet clinical response requires 2-4 weeks, suggesting secondary neuroadaptive processes.
Proposed mechanisms include downregulation of presynaptic autoreceptors, increased BDNF (brain-derived neurotrophic factor) signaling, and restoration of HPA axis function. Serotonin transporter (5-HTTLPR) polymorphisms predict antidepressant response: the long allele predicts better SSRI response (r=0
12-0 25, modest effect; Serretti et al. 2007). Neuroimaging shows reduced serotonin transporter availability in depression (Parsey et al. 2006) and reduced dopamine in striatum (Meyer et al. 2006).
Beck's Cognitive Triad and Cognitive Theory
Aaron Beck's cognitive theory (1967, 1976) identifies the cognitive triad of depression: negative view of self ('I am worthless'), negative view of world ('The world is demanding and defeating'), and negative view of future ('The future is hopeless'). Automatic negative thoughts are involuntary and habitual.
Beck demonstrated that depressed patients show negative cognitive biases: selective attention to negative information, overestimation of negative event probability, catastrophizing, and overgeneralization (Beck et al. 1979).
Compared to non-depressed controls, depressed individuals show 2-3x more automatic negative thoughts (Haeffel et al. 2005). The cognitive model explains why cognitive restructuring (CBT) is effective: modifying maladaptive thought patterns changes mood and behavior, creating positive feedback loops.
Neuroimaging shows depressed patients activate lateral prefrontal regions less during negative thought challenge (Ochsner et al. 2002).
STAR*D Trial and Treatment Algorithm
The Sequenced Treatment Alternatives to Relieve Depression (STAR*D) trial, the largest effectiveness trial of depression treatment (n=4,041), demonstrated a stepped algorithm approach (Trivedi et al. 2006). Level 1: citalopram (SSRI) monotherapy—41 8% remission rate (9 weeks). Patients not remitted moved to Level 2: switch to different class (bupropion, sertraline, venlafaxine) or augment with buspirone/bupropion—30 7% additional remission. Level 3 options (mirtazapine, nortriptyline, or augmentation with lithium/triiodothyronine): 15 9% additional remission. Level 4 (tranylcypromine ± augmentation): 13 7% additional remission. Cumulative remission across all levels: 67% (Gaynes et al. 2008). The trial showed that treatment resistance (failure to respond to two adequate antidepressant trials) occurs in ~33% and increases functional impairment more than baseline depression. Side effects and tolerability, not efficacy, drive treatment switches. Mean time to remission was 6-8 weeks per trial. Long-term follow-up showed 44% experienced relapse within 1 year post-remission (Perlis et al. 2006).