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(mĕnʹstroo-ŭm) [L. menstruus, menstrual fluid] A solvent; a medium. It was once believed that menstrual fluid had solvent qualities. SEE: vehicle.


(mĕnʹsū-ăl) [L. mensis, month] Monthly.


(mĕn-sū-rāʹshŭn) [L. mensuratio] The process of measuring.


(mentʹăl) [L. mens, stem ment-, mind] Pert. to the mind.


[L. mentum, stem ment-, chin] Pert. to the chin.

mental fog

Clouding of consciousness, usually with some loss of memory.


(men-talʹĭt-ē) Mental power or activity.

mentally ill

Affected by any condition that affects mood or behavior, such as depression, dysphoria, personality disorders, phobias, schizophrenia, or substance abuse, among others.

Mental Measurements Yearbook

A widely used index of commercially published, standardized tests.

mental retardation

Below average intelligence evident before the age of 18.

 INCIDENCE: Between 5 and 25 people out of every thousand have some degree of intellectual disability (ID). This is approximately the same number of people who have an Intelligence Quotient (IQ) of 70 or less. Severe intellectual disability is prevalent in about 0.5% of the population.

 CAUSES: In many persons, the cause is not identified. Injuries that occur during fetal or embryonic development (such as asphyxia or exposure to infections or toxins in utero); genetic syndromes (such as Tay-Sachs disease or Down syndrome); childhood exposure to toxins (such as lead); or social and emotional deprivation during infancy or childhood all may contribute to impaired intellectual development.

 SYMPTOMS AND SIGNS: Mental retardation is associated with impaired ability to learn; impaired communication; poor social, community or interpersonal adjustment, and, in some instances, inability to function independently, e.g., to support oneself financially, and to live safely and healthfully.

 DIAGNOSIS: Tests of intelligence quotient (IQ tests) are used to diagnose mental retardation, esp. when poor scores on these tests correlate with observed difficulties in adaptation to the environment.

 PREVENTION: Fetal alcohol syndrome, intellectual disability secondary to hypothyroidism, and some other forms of intellectual disability are preventable when they are detected early and interventions, e.g., maternal alcohol abstinence, are put into place. Patients with known genetic forms of mental retardation who want to avoid pregnancy may use contraception.

 TREATMENT: Treatment depends on the underlying cause and any associated neurological, endocrine, or gastrointestinal conditions. Many forms of congenital mental retardation are not directly treatable; associated conditions, such as seizures, are remediable with ...

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