[Physiology and physiopathology of somatic sensations studied in man by the method of evoked potentials]

The physiology of somatic sensation can be investigated noninvasively in man by recording the electric activity of peripheral nerves, spinal cord and brain. Since these responses have a small voltage, it is necessary to use electronic averaging methods for improving the signal-to-noise ratio. These methods are described and discussed, as well as principles of interpretation of somatosensory evoked potentials. It is agreed that the traces thus obtained involve a series of components (extracellular potentials) which reflect distinct neural generators. These generators have been identified and localized at different levels of the subcortical somatosensory pathway and in different cortical areas. Several components reflect generators located under the recording electrodes (nearfield potentials), while other reflect extracellular potentials diffusing at a distance in the volume conductor of the neck and head (farfield potentials). The analysis of these components provides a wealth of new data for the physiology and pathophysiology of the somatic sensory system in man. Besides so-called "obligatory" components that are present irrespective of the attention of the subject, the studies have uncovered "cognitive" components which reflect neural mechanisms involved in the intellectual processus of perception and decision.