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(BQ) Part 2 book "A concise guide to intraoperative monitoring" presents the following contents: Evoked activity, spine surgery, cranial surgery, artifacts and troubleshooting, closing remarks. | chapter 7 Evoked Activity 7.1 Introduction A clinically important tool in assessing the integrity of cortical and subcortical neuronal relays is the study of evoked responses ERs which result from external stimulation of a neural pathway. The rationale for using ERs intraoperatively is very simple all naturally occurring external stimuli detected by the sense organs such as sounds and lights are transmitted to the brain in the form of electrical signals through various sensory neural pathways. If these pathways are structurally and functionally intact the signals reaching the brain give rise to certain patterns of activity. Thus like the natural stimuli the delivery of experimental stimuli such as tones or electrical pulses and the simultaneous observation of the resulting patterns of activity provide an instantaneous display of the status of the sensory neural structures intervening between the stimulation and recording sites. ERs can be subdivided further into averaged and nonaveraged responses examples of which are the familiar evoked potentials EPs and the electrically triggered EMG respectively. In this chapter we present details on the use features stimulation and recording procedures as well as interpretation criteria of the various kinds of averaged and nonaveraged ERs. 7.2 Evoked Potentials An EP is the electrical response of the nervous system to external stimulation. There are two major types of EPs sensory and motor. In the former category a stimulus is delivered peripherally e.g. at a leg nerve and the resulting response is recorded centrally e.g. the cortex . In the latter category a stimulus is delivered centrally e.g. at the cortex and the resulting response is recorded peripherally e.g. at a leg nerve or muscle . Depending on the stimulus modality sensory EPs are divided into somatosensory auditory and visual indicated as SEPs AEPs and VEPs respectively. Early AEPs are referred to as brainstem auditory evoked responses BAERs . Motor EPs can be 89 .
