Escape learning in infant mice as a function of drive level and drive shifts during acquisition

Separate groups of 9-day-old Swiss-Webster mice began straight-alley escape training at .1 or .4 mA. After 12 trials, half of the mice in each group were shifted to .4 or .1 mA, respectively, whereas the remaining half continued at their original level for an additional 12 trials. Twenty-four hours later, half of each of the 4 shock-level groups were retested at .1 mA, half at .4 mA. The results indicated that those groups which made a large number of competing responses during early trials and showed a gradual reduction over training trials (.1-.1 and .1-.4) emitted the fewest number during retest at either shock level. In contrast, those groups with either limited (.4-.1) or no (.4-.4) opportunity to decrease competing responses during training showed evidence of poor (.4-.1) and no (.4-.4) retention of learned inhibition of that response. Running speed was clearly a performance measure, as it only reflected existing shock levels during both training and retention trials.