Premenstrual dysphoric disorder: A disorder marked by repeated experiences of significant depression and related symptoms during the week before menstruation.

Unipolar depression: Depression without a history of mania.

Norepinephrine: A neurotransmitter whose abnormal activity is linked to panic disorder and depression.

Serotonin: A neurotransmitter whose abnormal activity is linked to depression, obsessive-compulsive disorder, and eating disorders.

MAO inhibitor: An antidepressant drug that prevents the action of the enzyme monoamine oxidase.

Major depressive disorder: A severe pattern of unipolar depression that is disabling and is not caused by such factors as drugs or a general medical condition.

Depression: A low, sad state marked by significant levels of sadness, lack of energy, low self-worth, guilt, or related symptoms.

Bipolar disorder: A disorder marked by alternating or intermixed periods of mania and depression.

Electroconvulsive therapy (ECT): A treatment for depression in which electrodes attached to a patient’s head send an electrical current through the brain, causing a seizure.

Depressive disorders: The group of disorders marked by unipolar depression.

Mania: A state or episode of euphoria or frenzied activity in which people may have an exaggerated belief that the world is theirs for the taking.

Persistent depressive disorder: A chronic form of unipolar depression marked by ongoing and repeated symptoms of either major or mild depression.

Selective serotonin reuptake inhibitors (SSRIs): A group of second-generation antidepressant drugs that increase serotonin activity specifically, without affecting other neurotransmitters.

Tricyclic: An antidepressant drug such as imipramine that has three rings in its molecular structure.

Cyclothymic disorder: A disorder marked by numerous periods of hypomanic symptoms and mild depressive symptoms.

Vagus nerve stimulation: A treatment procedure for depression in which an implanted pulse generator sends regular electrical signals to a person’s vagus nerve; the nerve, in turn, stimulates the brain.

Interpersonal psychotherapy (IPT): A treatment for unipolar depression that is based on the belief that clarifying and changing one’s interpersonal problems will help lead to recovery.

Symbolic loss: According to Freudian theory, the loss of a valued object (for example, a loss of employment) that is unconsciously interpreted as the loss of a loved one. Also called imagined loss.

Cognitive therapy: A therapy developed by Aaron Beck that helps people identify and change the maladaptive assumptions and ways of thinking that help cause their psychological disorders.

Bipolar I disorder: A type of bipolar disorder marked by full manic and major depressive episodes.

Cognitive triad: The three forms of negative thinking that theorist Aaron Beck theorizes lead people to feel depressed. The triad consists of a negative view of one’s experiences, oneself, and the future.

Lithium: A metallic element that occurs in nature as a mineral salt and is an effective treatment for bipolar disorders.

Mood stabilizing drugs: Psychotropic drugs that help stabilize the moods of people suffering from a bipolar mood disorder. Also known as antibipolar drugs.

Transcranial magnetic stimulation (TMS): A treatment procedure for depression in which an electromagnetic coil, which is placed on or above a person’s head, sends a current into the person’s brain.

Deep brain stimulation (DBS): A treatment procedure for depression in which a pacemaker powers electrodes that have been implanted in Brodmann Area 25, thus stimulating that brain area.

Bipolar II disorder: A type of bipolar disorder marked by mild manic (hypomanic) and major depressive episodes.

Learned helplessness: The perception, based on past experiences, that one has no control over one’s reinforcements.

Second messengers: Chemical changes within a neuron just after the neuron receives a neurotransmitter message and just before it responds.