Electrophysiological measures visual evoked potentials

The International Association for the Study of Pain (lASP) has defined pain as an unpleasant sensory and emotional experience that is evoked by actual or potential noxious (i.e. tissue-damaging) stimuli or by tissue injury. Normally, pain is the subjective result of nociception. Nociception is the encoding and processing of noxious stimuli in the nervous system. It can be objectively measured with various techniques, i.e. with electrophysiological recordings. By contrast, pain as a subjective experience can be verbally or visually described by humans, and it cannot be measured objectively However, animals (as well as humans) show reflex responses to acute noxious stimuh, which can be assessed for the relationship between nociception and pain. 

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