Multimodal Learning of Pheromone Locations

Abstract

Memorizing pheromonal locations is critical for many mammalian species as it involves finding mates and avoiding competitors. In rodents, pheromonal sensing happens through both vomeronasal organ (VNO) and main olfactory epithelium (MOE). It remains unclear as to which modalities and cues are used by rodents to form these long-term memories efficiently. Here, we addressed this problem by training female mice on a multimodal task to locate pheromones by sampling volatiles emanating from male urine and associating with the dimensions of certain shapes sensed by their vibrissae. In this novel pheromone location assay, female mice' preference towards male urine scent decayed over time while permitting them to explore pheromones versus neutral stimuli, water. On training the animals for associations involving olfactory and whisker systems, they were able to memorize the location of opposite sex pheromones, when tested 15 days later. This memory was not formed either when the somatosensory inputs through whisker pad were blocked or pheromonal cues were replaced by that of same sex. On investigating the neural correlates of volatile pheromone information processing, we observed increased neurogenesis in the main olfactory bulb (MOB) after two weeks of learning. However, the pheromonal exposure induced Whitten effect, the estrous cycle synchronization, did not cause any differences in the MOB mediated discrimination learning pace for various non-pheromonal volatiles. Our study thus provides the evidence for associations formed between different sensory modalities facilitating the long-term memory formation in social and reproductive behaviors.