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la belle indifférence: The blasé attitude people with conversion disorder have toward their symptoms.

labelling theory: The general view that serious psychopathology, such as schizophrenia, is caused by society’s reactions to unusual behaviour.

labile: Easily moved or changed, quickly shifting from one emotion to another, or easily aroused.

language disorder: Difficulties understanding spoken language (receptive) or expressing thoughts verbally (expressive).

lanugo: A fine soft hair that develops on the bodies of people with anorexia nervosa.

latency period: In psychoanalytic theory, the years between ages six and twelve, during which id impulses play a minor role in motivation.

latent content: In dreams, the presumed true meaning hidden behind the manifest content.

lateral hypothalamus: A section of the brain that, if lesioned, is associated with a dramatic loss of appetite.

law of effect: A principle of learning that holds that behaviour is acquired by virtue of its consequences.

learned helplessness theory: The theory that individuals acquire passivity and a sense of being unable to act and to control their lives; this happens through unpleasant experiences and traumas against which their efforts were ineffective; according to Seligman, this brings on depression.

learning disabilities: General term for learning disorders, communication disorders, and motor skills disorder.

learning disorders: A set of developmental disorders encompassing dyslexia, mathematics disorder, and disorder of written expression and characterized by failure to develop in a specific academic area to the degree expected by the child’s intellectual level. Not diagnosed if the disorder is due to a sensory deficit.

learning (behavioural) paradigm: In abnormal psychology, a set of assumptions that abnormal behaviour is learned in the same way as other human behaviour.

least restrictive alternative
: The legal principle according to which a committed mental patient must be treated in a setting that imposes as few restrictions as possible on his or her freedom.

lesion: Any localized abnormal structural change in organ or tissue caused by disease or injury.

libido. See Eros.

Life Change Unit (LCU) score: A score produced by totaling ratings of the stressfulness of recently experienced life events; high scores are found to be related to the contraction of a number of physical illnesses.

life-span developmental psychology: The study of changes in people as they grow from infancy to old age.

lifetime prevalence rate: The proportion of a sample that has ever had a disorder.

limbic system: The lower parts of the cerebrum, made up of primitive cortex; controls visceral and bodily changes associated with emotion and regulates drive-motivated behaviour.

linkage analysis: A technique in genetic research whereby occurrence of a disorder in a family is evaluated alongside a known genetic marker.

lithium carbonate: A drug useful in treating both mania and depression in bipolar disorder.

lobotomy: A brain operation in which the nerve pathways between the frontal lobes of the brain and lower brain structures are cut in hopes of effecting beneficial behavioural change.

logotherapy: An existential psychotherapy, developed by Viktor Frankl, aimed at helping the demoralized client restore meaning to life by placing his or her suffering in a larger spiritual and philosophical context. The individual assumes responsibility for his or her existence and for pursuing a meaningful life.

longitudinal studies: Investigation that collects information on the same individuals repeatedly over time, perhaps over many years, in an effort to determine how phenomena change. Compare with cross-sectional studies.

loose associations (derailment): In schizophrenia, an aspect of thought disorder wherein the patient has difficulty sticking to one topic and drifts off on a train of associations evoked by an idea from the past.

LSD: d-lysergic acid diethylamide, a drug synthesized in 1938 and discovered by accident to be a hallucinogen in 1943.

Luria–Nebraska test: A battery of neuropsychological tests that can detect impairment in different parts of the brain.