Evoked potential

An evoked potential or evoked response is an electrical potential recorded from the nervous system of a human or other animal following presentation of a stimulus, as distinct from spontaneous potentials as detected by electroencephalography (EEG), electromyography (EMG), or other electrophysiological recording method.

Evoked potential amplitudes tend to be low, ranging from less than a microvolt to several microvolts, compared to tens of microvolts for EEG, millivolts for EMG, and often close to a volt for ECG. To resolve these low-amplitude potentials against the background of ongoing EEG, ECG, EMG, and other biological signals and ambient noise, signal averaging is usually required. The signal is time-locked to the stimulus and most of the noise occurs randomly, allowing the noise to be averaged out with averaging of repeated responses.

Signals can be recorded from cerebral cortex, brain stem, spinal cord and peripheral nerves. Usually the term "evoked potential" is reserved for responses involving either recording from, or stimulation of, central nervous system structures. Thus evoked compound motor action potentials (CMAP) or sensory nerve action potentials (SNAP) as used in nerve conduction studies (NCS) are generally not thought of as evoked potentials, though they do meet the above definition.

Prag

Prag may refer to:

Edgar Allan Poe

Edgar Allan Poe (/poʊ/; born Edgar Poe; January 19, 1809 – October 7, 1849) was an American writer, editor, and literary critic. Poe is best known for his poetry and short stories, particularly his tales of mystery and the macabre. Widely regarded as a central figure of Romanticism in the United States and American literature as a whole, he was one of the country's earliest practitioners of the short story. Poe is generally considered the inventor of the detective fiction genre and is further credited with contributing to the emerging genre of science fiction. He was the first well-known American writer to try to earn a living through writing alone, resulting in a financially difficult life and career.

Born in Boston, Poe was the second child of two actors. His father abandoned the family in 1810, and his mother died the following year. Thus orphaned, the child was taken in by John and Frances Allan, of Richmond, Virginia. Although they never formally adopted him, Poe was with them well into young adulthood. Tension developed later as John Allan and Edgar repeatedly clashed over debts, including those incurred by gambling, and the cost of secondary education for the young man. Poe attended the University of Virginia for one semester but left due to lack of money. Poe quarreled with Allan over the funds for his education and enlisted in the Army in 1827 under an assumed name. It was at this time his publishing career began, albeit humbly, with an anonymous collection of poems, Tamerlane and Other Poems (1827), credited only to "a Bostonian". With the death of Frances Allan in 1829, Poe and Allan reached a temporary rapprochement. Later failing as an officer's cadet at West Point and declaring a firm wish to be a poet and writer, Poe parted ways with John Allan.