depression

Meaning: Depression, or major depressive disorder, is a mood disorder. A person has a depressed mood or anhedonia (loss of interest or pleasure) for at least two weeks, with other symptoms such as disturbed sleep or appetite, low energy, poor concentration and feelings of worthlessness. Two accounts of its causes appear. The biological account links it to low activity of monoamine neurotransmitters (serotonin, norepinephrine), hippocampal changes and genetic risk. The cognitive and learning account points to learned helplessness (Seligman) and Beck's negative cognitive triad: negative views of self, world and future. In neuroscience, long-term depression (LTD) is a different idea: a lasting weakening of a synapse.

On the MCAT: Passages give a symptom list and ask you to classify it. A depressive episode with no mania is unipolar. Bipolar disorder includes manic or hypomanic episodes. Persistent depressive disorder is milder but lasts longer. You may predict that a treatment that raises serotonin or norepinephrine signaling would ease symptoms. You may also read a learned-helplessness design, in which animals given inescapable shocks later fail to escape avoidable ones. Sociology items link risk to factors such as social isolation and low socioeconomic status.

Common confusion: Depression as a disorder is not ordinary sadness. Diagnosis needs a set duration and impaired functioning. The monoamine link is a correlation and not a complete explanation, since the cognitive and social accounts also matter.