New ‘silent but responsive’ cells discovered in part of brain that processes smell

27 July 2014

A 'silent' population of brain cells in the olfactory network - the part of the brain that processes smell information - may play a key role in engaging local brain cell networks.

The finding comes from research led by scientists at the Medical Research Council's National Institute for Medical Research (NIMR; now part of the Francis Crick Institute).

The team discovered that a 'silent' subpopulation of nerve cells, or neurons, in the early olfactory processing network, are much more prominent than previously thought. They found that in the awake state, these neurons show very little activity if odor stimuli are not present, but they respond strongly to stimulation.

The researchers used a method called whole-cell patch clamp recordings to record electrical activity from  a large sample of 125 individual neurons in the brains of awake mice.

The technique is time consuming but avoids the problem of bias towards recording active cells. In contrast, most previous studies haven't looked at activity in the awake state, and silent and weakly active neuron populations have remained undetected.

Dr Mihaly Kollo of NIMR explained: "Our findings suggest that different neurons in this population communicate in different ways with the local network.

"For instance some neurons, such as the silent but strongly responding ones our team discovered, have better access to activate interneurons - cells involved in local processing of smell information."

Dr Andreas Schaefer of NIMR and University College London added: "Our results demonstrate that, in contrast to previous conclusions, overall neuronal activity in the awake state is not simply increased compared to the anesthetised state. Instead, it is characterised by an increase in variability and consequently both a larger number of very active cells as well as a substantial population of 'silent' neurons.

"Our large sample allowed us to make the striking finding that sensory responses are strongly influenced by ongoing activity, suggesting that a previously inaccessible population of 'silent' cells can exert a powerful influence over the olfactory bulb in the awake animal."

The work also has implications for other brain research. It raises the possibility that commonly used large-scale methods for measuring neuronal activity need to address the potential technical difficulties and biases in recordings discovered here.

The paper, ' Silent' mitral cells dominate odor responses in the olfactory bulb of awake mice, is published in Nature Neuroscience.

  • A study looking at the electrical activity of individual brain cells in awake mice has allowed researchers to find a previously undetected group of cells in the part of the brain that processes smells, known as the olfactory network. 
  • These cells appear to show little activity when no smell stimuli are present, but respond strongly to stimulation. 
  • The work involved collaboration between scientists at the Medical Research Institute's National Institute for Medical Research, University College London and the Max Planck Institute for Medical Research and the University of Heidelberg in Germany.