Abstract
In order to study the ability of olfactory discrimination, thirsty rats were trained to distinguish a water containing clove oil odor from a water containing anise oil odor and a drop of a rat repellent, naramycin (Tanabe Phamaceutical Comp.) for several days. Then, their ability of discrimination was tested for ten or more days. Experiments were performed on normal rats and on the rats with the anterior limbs of the anterior commissure sectioned, the lateral olfactory tracts sectioned or the olfactory bulbs removed uni- or bilaterally. Thus, the roles played in the olfactory discrimination by these olfactory elements were examined.
1. It was found that fresh untreated normal rats could discriminate these odors completely after training for about six days. When these rats were trained to discriminate between several pairs or odors, their conditioned reactions gradually grew faster.
2. When the olfactory bulbs were removed unilaterally in the fully conditioned rats, discriminative ability decreased once but then began to recover day by day, and recovered nearly completely in about twenty three days. However, it was made clear that the level of the discriminative ability by bilateral olfactory nervous systems can not be attained by a unilateral nervous system. Hemispheric predominance in the discriminative ability was not found between the bilateral olfactory bulbs.
3. Sectioning of the lateral olfactory tracts lowered the ability of the odor discrimination more markedly than sectioning of the anterior limbs of the anterior commissure. This is coincident with Allison's hypothesis that the lateral olfactory tract has finer ability of odor discrimination than the anterior commissure.
4. Rats with both the anterior limbs of the anterior commissure and the lateral olfactory tracts sectioned bilaterally showed better results in the learning ability of discrimination and in the recovery of the discriminative ability after the operation than the rats with the olfactory bulbs removed bilaterally. This suggests the presence of a third olfactory nervous pathway in addition to the above two ones.
5. It was clearly proved that the trigeminal nerve takes a part in the odor discrimination, but that role is not necessarily large.
