Primacy and recency effects in rhesus monkeys (Macaca mulatta) using a serial probe recognition task: II. Effects of atropine sulfate.

Nonhuman primates display both a primacy and a recency effect when trained on a 6-item serial probe recognition task. The author has previously shown that in the rhesus monkey, diazepam (3.2 mg/kg im) interferes with the memory processes that mediate the recency effect without affecting those memory processes involved in the primacy effect (C. A. Castro, 1995). This study assessed the effects of atropine sulfate (0.2, 0.3, and 0.4 mg/kg im) on the primacy and recency effects in these same monkeys. Opposite the effects of diazepam, atropine disrupted the primacy component of the serial position curve and had no measurable effect on the recency component. In addition, the 2 highest doses of atropine disrupted accuracy on the nonmatching probe trials, whereas all 3 doses of atropine resulted in increased response latencies. These reports indicate that the primacy and recency effects in the nonhuman primate can be pharmacologically dissociated.