The vast majority of neuroscience research is conducted using animal models. This, unfortunately, is the nature of the beast, and until non-invasive methods can reach a level where they can tell us something meaningful about how the human brain works, is likely to remain the case.
It is nice, therefore, when you stumble upon a bit of research that uses humans as lab-rats and, in their recent article ‘Neural activity at the human olfactory epithelium reflects olfactory perception’, Lapid and colleagues at the Weizmann Institute of Science in Israel did exactly that.
The title of the article is ostensibly complicated, but really it just means that the activity of the receptors in your nose (olfactory=sense of smell) are organised in such a way as to represent the perception of the smells that activate them. You see, in your other senses, there is an organisation of the receptive field that relates to the thing being sensed. For example, the sensory cells in your retina are organised such that each cell represents a point in space. In your ear, cochlear coordinates represent tone. In contrast, it had been assumed that olfactory receptors responding to different smells are distributed along the inside of your nose in a uniform, random way.
However, Lapid and colleagues smelled a rat in this hypothesis and decided to directly test whether or not this was actually the case. They did this by sticking electrodes up the nasal cavity of human subjects and presenting them with a set of different odors; an experimental paradigm that really must have got up people’s noses.
The authors hypothesised that, as with sight and sound, smell receptors are highly organised and that this organisation was based upon the pleasantness of the smell. In order to test this, they used two complementary approaches. Firstly, they held an electrode in one place in the nasal epithelium and presented subjects with odors that ranged from unpleasant to pleasant. Secondly, they moved the electrode within subjects to measure responses to a single odor. In both cases, the authors demonstrated that there are areas in the nose that are finely-tuned to respond to certain smells and not to others, indicating organisation.
The authors also showed that this organisation seems to reflect the perceived pleasantness of the odorant, which raises some interesting questions. For example, some people find certain smells delectable whereas others find them vile. Is this variability due to differences in the way that the smell receptors are organised or it because people’s experiences have led to alterations in brain structure upstream of the receptors themselves, such as in the olfactory bulb or in the neocortex?
I guess the appropriate answer to that is ‘who nose?’ I shall stop now.
To read the original article, click here, but you’ll need a subscription to nature.