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RESEARCH PRODUCT

The Adequate Stimulus

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The term adequate stimulus describes that class of environmental phenomena that requires the least amount of energy to elicit a percept mediated by a particular sensory system, implying that the receptive organs of that sensory system are specialized to detect those phenomena. It was difficult to transfer this concept to the perception of pain and to the nociceptive system. Many different stimuli may cause pain (pin prick, burn injury, freeze injury, inflammation, etc.), none of which needs particularly low amounts of energy. The common denominator of those stimuli is that they threaten to cause tissue damage (in Greek: νoξη Noxe). Hence the adequate stimulus to elicit pain is traditionally called a noxious stimulus, defined as An actually or potentially tissue damaging event. But not all noxious stimuli are detected by the nociceptive system (e.g., sunburn of the skin, damage to solid visceral organs). Therefore, the adequate stimulus for this system in the strict sense is that subset of noxious stimuli that can be encoded by the nociceptive system (nociceptive stimuli). It is not unusual for a sensory system to encode only a part of the range of environmental phenomena that its receptive organs are specialized for (cf. visual stimuli or auditory stimuli). Likewise, nociceptive stimuli consist of a restricted range of actually or potentially tissue-damaging events.