Habenular lesions and discrimination responding to olfactory and visual stimuli

Abstract

Twenty albino rats with either bilateral habenular lesions or sham operations were trained to discriminate on the basis of olfactory cues between two compartments of a Grice apparatus modified for odor presentation. The discriminative stimulus consisted of different relative concentrations of the odor substance Lilial ranging from 0.1% to 10% air-diluted concentrations. The animals were initially trained using a 10% relative odor stimulus and subsequently tested with a descending series of odorant concentrations. All animals except one acquired the initial discrimination, but successive lowering of the odor concentration disrupted the performance of the experimental group while all controls successfully reached criterion at the lowest concentration used. The rat failing to make the initial odor discrimination was able to discriminate between the two compartments when a visual cue was substituted for the olfactory stimulus. We conclude that the habenular area serves as an important link between olfactory sensory input and motor systems in the rat. It appears that the behavioral changes observed are related more to threshold elevation or an impairment in olfactory integration than to generalized disruption of response inhibition mechanisms.