‘Light-smelling’ mice may explain how we distinguish between scents

LONDON - Harvard University neurobiologists have created mice that can ’smell’ light, a study that could help researchers better understand the neural basis of olfaction.

Venkatesh N. Murthy and his colleagues at Harvard and Cold Spring Harbor Laboratory used light, applying the infant field of optogenetics to the question of how cells in the brain differentiate between odours.

Optogenetic techniques integrate light-reactive proteins into systems that usually sense inputs other than light. Murthy and his colleagues integrated these proteins, called channelrhodopsins, into the olfactory systems of mice, creating animals in which smell pathways were activated not by odours, but rather by light.

With the optogenetically-engineered animal, the scientists were able to characterize the patterns of activation in the olfactory bulb, the brain region that receives information directly from the nose.

Because light input can easily be controlled, they were able to design a series of experiments stimulating specific sensory neurons in the nose and looking at the patterns of activation downstream in the olfactory bulb.

But it turns out that the spatial organization of olfactory information in the brain does not fully explain our ability to sense odours. The temporal organization of olfactory information sheds additional light on how we perceive odours.

In addition to characterizing the spatial organization of the olfactory bulb, the new study shows how the timing of the “sniff” plays a large part in how odours are perceived.

The study has implications not only for future study of the olfactory system, but more generally for teasing out the underlying neural circuits of other systems.

The study is described this week in the journal Nature Neuroscience. (ANI)