Chapter 13 - Recording Evoked Potentials

Abstract

Publisher Summary This chapter discusses the recording of revoked potentials. Evoked potentials can be and have been recorded in many places in the brain. It is conceivable, for example, to have electrodes in the cochlear nucleus, medial geniculate, primary auditory cortex, and secondary auditory cortex and then record the successive potentials in these loci along the auditory path in response to a natural auditory stimulus, such as a brief click or tonal pip, or in response to electrical stimulation of the eighth cranial nerve. Evoked potentials have been and are still employed in this way to map connections in the nervous system. Often, it has been the case that although a pathway between two structures is not readily demonstrable with anatomical or histological methods, the stimulation of one structure nonetheless evokes potentials in the other, a datum that would strongly suggest a connection between the two. Similarly, evoked potentials have been employed traditionally to localize a structure to be stimulated or ablated later. The introduction of a larger electrode into or upon the surface of the brain may result in a recording, which integrates the activities of many cells. It is at present possible to record either the higher frequency spike activity from many cells at once (a population measure called hash) or the lower frequency macropotentials, which are presumably sums of all post-synaptic potentials from all cells in the region of the recording electrode. The latter events, when spontaneous, are generally referred to as the electroencephalogram (EEG). It is possible to intentionally activate a given neural pathway via natural or electrical stimulation. The macropotential integral of post-synaptic potentials resulting from stimulus bound activity is called an evoked potential.