Discriminative properties of aversive electrical stimulations of the so-called "mesencephalic locomotor region": a parametric study.

The classical 2-lever food-reward-reinforced discrimination paradigm, although already successfully applied to study discriminative properties of positively reinforcing electrical brain stimulations (EBS), has not yet been used for negatively reinforcing (aversive) EBS. This study was aimed at assessing if such a discrimination paradigm could be used to demonstrate discriminative properties of aversive EBS of the so-called "mesencephalic locomotor region" (MLR). Fourteen rats were trained for food reward to press one lever in the presence of EBS of the MLR and the other lever in the absence of EBS. Discriminative control by EBS of the MLR was obtained in 11 rats, which were subsequently subjected to a parametric study. It was found that the discriminative properties of EBS of the MLR covaried with changes in the intensity, frequency and pulse duration of the EBS. Our data also suggest that the aversive dimension of the stimulation might constitute a component of the discriminative cue induced by these EBS.