Basic Techniques of Evoked Potential Recording

Abstract

The electrical activity arising from peripheral and central nervous systems may be subdivided broadly into spontaneous activity, e.g., electroencephalogram (EEG), and evoked potentials (EPs). The latter are time-locked and follow a fixed time period in response to a discrete sensory stimulus. Evoked potentials are mainly of two types: 1. Stimulus-related EPs: They occur with short latency (greater than 1.50 msec) and elicited by stereotype stimuli of specific modality. Examples are brainstem auditory, visual, somatosensory, and motor evoked potentials. 2. Event-related EPs: These are late potentials (e.g., P300), which are dependent on the information content of the stimulus. They appear when a subject "attends" to a "meaningful" stimulus. These EPs are not stimulus specific; equivalence in "task relevance" is the major determining factor in their elicitation. The stimulus-related EPs are utilized most for diagnostic purposes. These will constitute the main subject for discussion in this text.