The four commonly used central pain stimuli are:

Take ten volunteer subjects, subject them to a pain stimulus accompanied by certain words and sounds and images.

In some conditions, excitation of pain fibers becomes greater as the pain stimulus continues, leading to a condition called hyperalgesia.

Dr. Spiegel found that the hypnotic instructions significantly reduced both parts of the response to a pain stimulus.

It signals high alert even when there's little pain stimulus.

In Nancy Greenly's case the only test would be reaction to pain stimulus.

He realized then that the itch and the pain stimuli did not derive from his own body.

After an initial titration period, doses may remain stable for long periods (months to years) if the pain stimulus remains unchanged.

Eye opening in response to pain stimulus.

It is impossible to imagine a creature larger than a flea without fears and hopes, or some such equivalent structure based on pain stimuli.