Brain can compensate for reduced olfactory input

13 May 2016

Reducing the number of different smell receptors in the nose of a mouse doesn't affect its ability to detect or differentiate smells, according to research by Francis Crick Institute scientists and international collaborators.

The researchers say that this is because the brain compensates and can still obtain useful information from greatly reduced sensory input.

Mice have around 1,300 different odour receptors in their noses. In previous research, Dr Fleischmann and colleagues from College De France and Columbia University created mice with a 'monoclonal nose' - where 95 per cent of their smell receptors were the same, reducing the range of receptors by 20-fold. Dr Fleischmann's team worked with Dr Andreas Schaefer and his team at the Crick in the current study.

Dr Schaefer explained: "Exposure to odours elicits neural activity patterns in the brain that are thought to be the building blocks for odour perception and behaviour. Upsetting the neural circuits that detect and process olfactory information can help us understand how the brain enables smell-driven behaviours."

The scientists proposed that, even though their smell input was hugely reduced, the neural circuits in the brains of the mice would make up for this and still allow them to extract useful information from what they could smell. To test this idea they analysed brain activity of the mice in response to smells using imaging techniques and electrophysiology in awake mice.

They found that relevant parts of the brain were indeed capable of generating largely normal patterns of brain activity in response to odours, despite massively degraded sensory input. Furthermore, the researchers found that this 'normalisation' of brain activity patterns relied on the tightly balanced interplay between neural excitation and inhibition.

Dr Schaefer said: "Our research strongly suggests that degraded sensory signals can be transformed by neural circuits in the brain to extract useful information.

"Our findings thus provide an important link between sensory input, neural mechanisms of sensory information processing, and behavioral output."

The paper, Massive normalization of olfactory bulb output in mice with a 'monoclonal nose', is published in eLife.

  • The brain can compensate for reduced olfactory - sense of smell - input and still obtain useful information, according to new research in mice.
  • For the study, Andreas Schaefer, Rebecca Jordan and Izumi Fukunaga at the Crick worked with Dr. Alexander Fleischmann's team from Collège de France in Paris, as well as colleagues from University College London, Massachusetts Institute of Technology and Duke University, both in the USA.