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

Previous electrophysiological studies and computational modeling suggest th e hypothesis that cholinergic neuromodulation may reduce olfactory associat ive interference during learning (M. E. Hasselmo, B. P.Anderson, & J. M. Bo wer, 1992; M. E. Hasselmo & J. M. Bower, 1993). These results provide behav ioral evidence supporting this hypothesis. A simultaneous discrimination ta sk required learning a baseline odor pair (A+B-) and then, under the influe nce 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 predi cted by the model, rats that received scopolamine (0.50 and 0.25 mg/kg) wer e more impaired at acquiring overlapping than nonoverlapping odor pairs rel ative to their performance under normal saline or methylscopolamine. These results support the prediction that the physiological effects of acetylchol ine can reduce interference between stored odor memories during associative learning.