132 • Alternatives to Animal Use in Research, Testing, and Education 
food as and when it wants to eat. In this way, 
any deprivation would be self-imposed as 
under natural conditions (121,151). This tech- 
nique has been used successfully in work on 
sensory -motor functioning in monkeys (168). 
Pain Research and the Use of 
Electric Shock 
The experience of pain is a highly adaptive ca- 
pacity. It prevents organisms from engaging in be- 
haviors that would otherwise prove maladaptive. 
For example, humans who are congenitally insen- 
sitive to pain become terribly scarred and muti- 
lated, often develop a sense of being invincible, 
and have short life expectancies (141, 143, 196). Per- 
haps because pain plays such an essential role in 
regulating the behavior of organisms, pain thresh- 
olds are surprisingly consistent across a great 
diversity of species (115). The discovery of en- 
dogenous opiates in earthworms (5) and recent 
findings with spiders (61) suggest that inverte- 
brates may also feel pain. 
Pain can be induced through mechanical, ther- 
mal, electrical, or chemical stimuli (127). Of the 
various stimuli used for research purposes, elec- 
tric shock at the levels normally used in experimen- 
tation is the only one that does not damage tissue. 
Most studies of pain in animals use what are called 
flinch -and-jump thresholds— an index of the min- 
imal amount of electric shock or heat needed to 
produce a reaction. Electric shock is used as a 
stimulus for research into the mechanism of pain 
for several reasons: 
• Electric shock is easily quantifiable. The pa- 
rameters of shock can be manipulated and 
specified with a high degree of precision over 
a wide range. 
• Electric shock can be administered so as to 
have a discrete or gradual onset and offset. 
• Electric shock of the type most often used (i.e., 
a brief current of 0.001 amperes, the equiva- 
lent of a tingling sensation in the finger) does 
not yield physical damage, bleeding, or tissue 
destruction. 
However, electric shock is a highly atypical stimu- 
lus (79). No contemporary terrestrial species ap- 
pears to have evolved under conditions of elec- 
tric shock. The question of whether data obtained 
this way are widely generalizable in mechanisms 
of pain remains unanswered. 
A survey of the 608 articles appearing from 1979 
through 1983 in the American Psychological Asso- 
ciation journals that typically publish animal re- 
search (e.g., Journal of Comparative and Physio- 
logical Psychology and its successors Behavioral 
Neuroscience and Journal of Comparative Psychol- 
ogy) identified 10 percent of the studies as using 
electric shock. Four percent of the studies admin- 
istered inescapable shocks stronger than 0.001 am- 
peres. Most of the experiments with electric shock 
involved rodents; those with monkeys, dogs, and 
cats accounted for 0.5 percent of the total 608 arti- 
cles (43). 
Recommendations that have been made to re- 
duce pain or discomfort in animal experiments in- 
volving aversive stimulation include: 
• The lowest possible level of electric shock 
should be used that will at the same time main- 
tain the behavior under study (52). However, 
this may reduce the statistical power and re- 
quire a large sample size. 
• Animals should be given predictable rather 
than unpredictable shock and an opportunity 
to control its termination (52). Rats, for ex- 
ample, will choose to receive more shocks at 
greater intensity in order to receive a warn- 
ing cue prior to each shock delivery (10). 
• If aversive stimulation must be used, alterna- 
tives to electric shock such as loud noise or 
bright lights should be considered (121). 
• In developing models of chronic pain, the 
model should closely simulate a particular 
chronic pain syndrome in humans (e.g., arthri- 
tis or cancer). Otherwise, there is no justifi- 
cation for the procedure (114). 
• Animals should have an opportunity to con- 
trol the intensity of the stimulus in chronic 
pain studies . While the objection to this might 
be that, given this option, the animal would 
“turn off” the pain stimulus, this might be cir- 
cumvented by giving a preferred food reward 
for keeping the stimulus “on” at a given level, 
as in experiments with electric shock titration 
techniques (114). 
• A reward, such as a preferred food, should 
be used for the correct responses instead of 
a punisher, such as electric shock, for incor- 
rect response (121). 
