An algedonic signal is a pre-emptive message concerning pleasure or pain.
[1] An arousal mechanism can generate an algedonic signal, and thus provide an important survival mechanism to a living organism by alerting it to a threat.
An example of the disastrous consequences of such a system not being in place is that of a moth attracted by the light of an open flame without recognising the danger of fire.
In the human nervous system a variety of algedonic signals are brought together in the midbrain reticular formation from across the whole body.
[2] A source of pain, such as touching a burning surface or treading on broken glass, creates such an algedonic signal which interrupts consciousness and provokes a reflex action.