ScienceDaily has an item (here) on a paper by Plailly, Delon-Martin and Royet on learning to imagine odours, something that most people are unable to do. They show it is a learned skill.
Here is the paper’s abstract:
Areas of expertise that cultivate specific sensory domains reveal the brain’s ability to adapt to environmental change. Perfumers are a small population who claim to have a unique ability to generate olfactory mental images. To evaluate the impact of this expertise on the brain regions involved in odor processing, we measured brain activity in novice and experienced (student and professional) perfumers while they smelled or imagined odors. We demonstrate that olfactory imagery activates the primary olfactory (piriform) cortex (PC) in all perfumers, demonstrating that similar neural substrates were activated in odor perception and imagination. In professional perfumers, extensive olfactory practice influences the posterior PC, the orbitofrontal cortex, and the hippocampus; during the creation of mental images of odors, the activity in these areas was negatively correlated with experience. Thus, the perfumers’ expertise is associated with a functional reorganization of key olfactory and memory brain regions, explaining their extraordinary ability to imagine odors and create fragrances.
The activation of the primary olfactory cortex is similar to the way that visual and auditory mental imagery uses their primary sensory cortex regions to produce images as well as perception. In other words our brain generates its own sensation.
As perfumers become more skilled, they have to rely less on memory. Processing becomes more streamlined with training, resulting in reduced activation of hippocampus and other areas.
In this study, the perfumers were able to imagine the odors rapidly, sometimes instantaneously, whereas the students experienced some difficulties and needed to concentrate their attention. By easily reactivating the mnesic representations of odors, perfumers can mentally compare and combine scents with the aim of creating new fragrances.
My opinion is that we can learn to make many things conscious with training. Some people learn to control bodily functions like heart rate by watching a needle on a dial. What seems to be needed is a good deal of motivation and some feedback channel to compare signal with perception or a ‘language’ to describe phenomena ie a mapping to something that is easily made conscious like words or sights/sounds. It seems that only a few hundred people in the world are motivated to be perfumers. There are probably only a small number of professional ‘noses’ in other fields.