Primacy and recency effects in rhesus monkeys (Macaca mulatta) using a serial probe recognition task. I. Effects of diazepam.

In this study, we evaluated the effects of diazepam (0.2, 0.8, 1.6 and 3.2 mg/kg; IM) on the primacy and recency memory effects in four rhesus monkeys trained on a six-item serial probe recognition (SPR) task. Only the highest dose of diazepam (3.2 mg/kg) consistently affected the shape of the monkeys' serial position curves. Accuracy on the probe trials was disrupted for list items which occurred in the middle portion and recency memory component of the serial position curve, without affecting the primacy component. Diazepam, however, also produced several nonspecific effects on SPR performance. Both the 1.6 and 3.2 mg/kg diazepam doses disrupted accuracy on the non-matching probe trials, and the 3.2 mg/kg dose caused an increase in response latencies which were unrelated to any one component of the serial position curve. This is the first demonstration in nonhuman primates showing that the primacy and recency memory effects can be differentiated on the basis of diazepam dose.