Research in the area of pain, particularly a model of hyperalgesia that was created and investigated by our professor, Eric Weirtelak, suggests that the perception of pain extends beyond the area of damaged tissue, and can be influenced by our previous experiences. In the experiment, rats undergo the tail flick test to determine their baseline (or normal) pain sensitivity. The tailflick test consists of a little metal box with a hole in the top. Inside the box is a lightbulb. The rat's tail is put over the hole in the box and the lightbulb is turned on. When the rat feels the heat of the lightbulb it flicks it's tail away from the box. The time from when the light is turned on to when the rats flicks it's tail is the measure of pain sensitivity. When the rat is given an injection of LiCl it becomes hyperalgesic over its entire body for several hours. When the tailflick test is given after the LiCl injection one sees that the rat flicks its tail away from the tailflick box more quickly than before as now it is more sensitive to pain.
The second part of the experiment involves giving the rat access to water flavored with saccharine after the injection. The rat still becomes ill, but on later presentations of the same taste the rat will become hyperalgesic. This is because it associates the taste with the pain sensation. When offered the choice between the saccharine water and regular water the rat will refuse the saccharine water. Thus the rat's past experience with the saccharine water influences how it feels when presented with it again. Most people have had a similar experience, when they get sick and associate their illness with the last thing they eat. That last meal when thought of again, makes one cringe and feel sick. So it is fairly likely that the particular food or meal will be avoided in the future.