Olfactory functioning and callosotomy: a report of two cases

Two callosotomy patients with presumably intact anterior commissures were evaluated on a battery of olfactory tasks including sensitivity, discrimination, memory, identification, cross-modality matching, bilateral summation (dirhinic vs. monorhinic thresholds), and localization of odorants. One case was evaluated both pre- and post-surgery. He showed marked decrements after surgery in odor memory and in matching across modalities. After surgery, both patients were better able to name odorants presented to the left nostril than the right nostril. The patient who was asked to remember odorants that could be readily labeled was better able to remember those odorants presented to the left nostril. The findings that both cases performed equally well whether olfactory and tactile information was projected to the same hemisphere or a different one, that some bilateral summation was evident, and that the cases were unable to localize odorants suggests that the remaining neuronal pathways allow for some communication between hemispheres.