Assessment of shock discrimination in rats with signal detection theory

Nociception in six rats was evaluated with signal detection theory (TSD) techniques using a modified “yes-no” paradigm. A .1-sec, .075-mA shock was the discriminative stimulus for a choice to one side of a T-maze, and a .1-sec, .25-mA shock (capable of reliably eliciting a “flinch”) was the discriminative stimulus for the opposite choice. Response bias was manipulated through differential reinforcement for the two choices, and signal sensitivity was manipulated by varying the intensity of the higher intensity shock signal. Individual detection ROCs appeared linear with slopes of one when plotted on double-probability scales. Indices of signal sensitivity and response bias were independent, as predicted by TSD. Morphine sulfate (4 mg/kg) significantly reduced d’ but did not affect β, suggesting that, if appropriate parameters are used, TSD analyses may have value in assessing nociception in rats.