ABSTRACT
Pain research has always been hampered by the subjective nature of the phenomenon. In addition to the complexities of the independent variables being applied, pain researchers have also faced interpretational challenges related to the dependent variables being measured. The existence of pain in laboratory animals can never be ascertained with certainty, merely inferred from behaviors (e.g., withdrawal, licking, immobility, vocalization). Physiological signs (e.g., autonomic changes, EEG, evoked potentials) have proven to be even less reliable as indices of pain, since they
can be produced by arousing and/or threatening stimuli in the absence of pain.
