The Somatosensory Evoked Potential

Abstract

Three decades have elapsed since Dawson (1947) recorded the first somatosensory evoked potential (SEP). Simple superimposition of individual responses was possible because the patient had progressive myoclonic epilepsy. In this disease the SEP amplitude is much enhanced (Shibasaki et al, 1978; Kelly et al, 1981). Subsequently Dawson (1951, 1954) presented his averager to the Physiological Society, thereby initiating the present-day explosive growth of evoked potentials.SEPs are made up of components with varying latencies. The components are best identified by latency and polarity as recorded at the scalp (P = positive and N = negative). Nevertheless, the nomenclature of somatosensory evoked potentials can be extremely confusing, mainly because the same component can have a different polarity depending on the electrode montage used. Generally speaking (but this is not a firm rule), far-field (subcortical) potentials are positive in polarity when a non-cephalic reference is used, whereas these same components have a negative polarity when the reference is on the scalp. It is therefore useful to always indicate the recording montage being employed. In addition, use of absolute latencies in the terminology can cause confusion because they are dependent upon length and body height. For example, the brachial plexus component usually occurs at about 9 msec, but may extend to as long as 11 or more msec in a very tall individual. Subsequent components then become difficult to identify in relation to normal means.

Repair of electrically injured median nerve with the aid of somatosensory evoked potential

“…The latency of SSEP is mainly corresponding to the integrity of nerve's sheath, and the amplitude reflects the quantity of functional axons. According to previous reports, [21][22][23] the normal amplitude of SSEP in median nerve ranges from 2.5 to 3.1 lv. The amplitude of 2.5 lv was selected as the criterion for determination of the healthy nerve in our procedure.…”

“…Then the stimulus were given to the nerve at interval of 0.5 cm as the electrode moved proximally until to the site where the SSEP amplitude of 2.5 lv was elicited. [21][22][23] This point was regard as suitable plane for nerve resection. In some cases, the amplitude of SSEP was still lower than 2.5 lv even when the stimulate electrode reached the bifurcation of the anterior interosseous nerve.…”

Findings of Somatosensory Evoked Potential to Stimulation of the Sciatic Nerve in Two Different Rat Strains.

“…There are many studies about EP in humans as well as animals, but there is no study to compare SEP findings on different laboratory rat strains. SEPs and their neural generators are described in many reports [3,[4][5][6]. Scalp recordings show not only cortex-generated potentials, but also far field (Ff) potentials which are generated by structures far from the active electrode and reach the recording site by volume conduction.…”

“…Central conduction time (CCT) [3,5,11] is a kind of interpeak latency measurement and gives information about intracranial lesions.…”

Electrophysiological Detection of the Neurotoxic Effects of Acrylamide and 2,5-Hexanedione on the Rat Sensory System

“…Somatosensory evoked potentials (SEP) are also used in human medicine for evaluation of neurological disorders. The median nerve is stimulated and waveforms are recorded at successive intervals between the stimulus site and cortex (Dyer 1985;Eisen 1982;Otto 1986;Starr 1978).…”