Muscarinic cholinergic neuromodulation reduces proactive interference between stored odor memories during associative learning in rats.

Previous electrophysiological studies and computational modeling suggest the hypothesis that cholinergic neuromodulation may reduce olfactory associative interference during learning (M. E. Hasselmo, B. P. Anderson, & J. M. Bower, 1992; M. E. Hasselmo & J. M. Bower, 1993). These results provide behavioral evidence supporting this hypothesis. A simultaneous discrimination task required learning a baseline odor pair (A+B-) and then, under the influence of scopolamine, a novel odor pair (A-C+) with an overlapping component (A) versus a novel odor pair (D+E-) with no overlapping component. As predicted by the model, rats that received scopolamine (0.50 and 0.25 mg/kg) were more impaired at acquiring overlapping than nonoverlapping odor pairs relative to their performance under normal saline or methylscopolamine. These results support the prediction that the physiological effects of acetylcholine can reduce interference between stored odor memories during associative learning.