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Sperry, Roger Wolcott

(Encyclopedia)Sperry, Roger Wolcott, 1913–94, American biologist, b. Hartford, Conn., Ph.D. Univ. of Chicago, 1941. He studied zoology before teaching biology at the Univ. of Chicago (1946–52) and the Californi...

feedback

(Encyclopedia)CE5 Basic feedback control system feedback, arrangement for the automatic self-regulation of an electrical, mechanical, or biological system by returning part of its output as input. A simple exam...

Parkinson's disease

(Encyclopedia)Parkinson's disease or Parkinsonism, degenerative brain disorder first described by the English surgeon James Parkinson in 1817. When there is no known cause, the disease usually appears after age 40 ...

stuttering

(Encyclopedia)stuttering or stammering, speech disorder marked by hesitation and inability to enunciate consonants without spasmodic repetition. Known technically as dysphemia, it has sometimes been attributed to a...

toxoplasmosis

(Encyclopedia)toxoplasmosis, infection caused by Toxoplasma gondii, a single-celled parasitic microorganism that can infect most warm-blooded animals but reproduces only in animals of the cat family, who shed the p...

obesity

(Encyclopedia)obesity, condition resulting from excessive storage of fat in the body. Obesity is now usually defined using a formula known as the body mass index (BMI), in which weight (in kilograms) is divided by ...

infarction

(Encyclopedia)infarction, blockage of blood circulation to a localized area or organ of the body resulting in tissue death. Infarctions commonly occur in the spleen, kidney, lungs, brain, and heart. The acute emerg...

Hubel, David Hunter

(Encyclopedia)Hubel, David Hunter hyo͞oˈbəl [key], 1926–2013, American neurobiologist, b. Ontario, Canada, to American parents. In 1958, Hubel joined Torsten Wiesel at Johns Hopkins; the two relocated to Harva...

learning disabilities

(Encyclopedia)learning disabilities, in education, any of various disorders involved in understanding or using spoken or written language, including difficulties in listening, thinking, talking, reading, writing, s...

serotonin

(Encyclopedia)serotonin sĕrˌətōˈnĭn [key], organic compound that was first recognized as a powerful vasoconstrictor occurring in blood serum. It was partially purified, crystallized, and named in 1948, and it...