Selective loss of cholinergic neurons projecting to the olfactory system increases perceptual generalization between similar, but not dissimilar, odorants

The neuromodulator acetylcholine is thought to modulate information process ing in the olfactory system. The authors used 192 IgG-saporin, a lesioning agent selective for basal forebrain cholinergic neurons, to determine wheth er selective lesions of cholinergic neurons projecting to the olfactory bul b and cortex affect odor perception in rats. Lesioned and sham-operated rat s were tested in an olfactory generalization paradigm with sets of chemical ly related odorants (n-aliphatic aldehydes, acids, and alcohols). Lesioned rats generalized more between chemically similar odorants but did not diffe r from controls in their response to chemically unrelated odorants or in ac quisition of the conditioned odor. Results show that cholinergic inputs to the olfactory system influence perceptual qualities of odorants and confirm predictions made by computational models of this system.