Describe the signal averaging technique for measuring weak evoked electrical responses from the brain with scalp electrodes

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Medical Sciences

Describe the signal averaging technique for measuring weakevoked
electrical responses from the brain with scalp electrodes

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An evoked potential or evoked response is an electrical potential in a specific pattern recorded from a specific part of the nervous system especially the brain of a human or other animals following presentation of a stimulus such as a light flash or a pure tone Different types of potentials result from stimuli of different modalities and types EP is distinct from spontaneous potentials as detected by electroencephalography EEG electromyography EMG or other electrophysiologic recording method Such potentials are useful for electrodiagnosis and monitoring that include detections of disease and drugrelated sensory dysfunction and intraoperative monitoring of sensory pathway integrity 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 20 millivolts for ECG To resolve these lowamplitude potentials against the background of ongoing EEG ECG EMG and other biological signals and ambient noise signal averaging is usually required The signal is timelocked 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 Evoked potential is different from eventrelated potential ERP although the terms are sometimes used synonymously because ERP has higher latency and is associated with higher cognitive processing Sensory evoked potentialsEdit Sensory evoked potentials SEP are recorded from the central nervous system following stimulation of sense organs for example visual evoked potentials elicited by a flashing light or changing pattern on a monitorauditory evoked potentials by a click or tone stimulus presented through earphones or tactile or somatosensory evoked potential SSEP elicited by tactile or electrical stimulation of a sensory or mixed nerve in the periphery Sensory evoked potentials have been widely used in clinical diagnostic medicine since the 1970s and See Answer

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