Slow and fast signals in same part of brain controlled independently

07 July 2014

Reconstruction of an olfactory bulb neuron.

Image: Reconstruction of an olfactory bulb neuron.

Separate circuits within the same brain region can independently control activities on different time scales, according to research led by scienctists at the Medical Research Council's National Institute for Medical Research (NIMR; now part of the Francis Crick Institute).

The findings will enable future work to manipulate slow and fast events independently, and hopefully lead to greater understanding of how signal communication happens in the brain. The complexity of the brain means that many diseases that affect it are currently poorly understood, and it's hoped that the work will eventually lead to new ways to tackle these conditions.

Dr Izumi Fukunaga of NIMR explained: "Activities in the brain are regulated on different time scales. Some events are slow (3 to 10 cycles every second) while some are fast (50 to 100 cycles a second). These can happen simultaneously within the same brain region."

The team used a powerful method called optogenetics, which uses light to switch on or off a specific set of brain cells, or neurons. This allowed them to disrupt brain circuits fast and reversibly, to investigate how taking away a specific part of the circuit affects the function of a brain region.

They carried out their work in the mouse olfactory bulb, which transmits information about smells from the nose to the brain. The olfactory bulb is a classic example of a place in which fast and slow rhythms coexist. Two key types of neuron are anatomically segregated in the olfactory bulb, making the dissection of circuits carried out in this work feasible.

The researchers found that slow and fast activities are controlled by distinct circuits of brain cells. Neurons in the so-called 'glomerular layer', the layer where complex processing of signals from the nose first occurs in the brain, shape the slow activity, while neurons in the second, deeper layers, called 'granule cells', coordinate fast signals. This way, slow and fast events can be controlled independently.

Dr Andreas Schaefer of NIMR said: "Diseases affecting the brain are one of the leading medical concerns currently. Due to the complexity of the brain, still very little is understood about how circuits in the brain are wired and function. Understanding this will be a crucial step towards effective treatments."

The paper, Independent control of gamma and theta activity by distinct interneuron networks in the olfactory bulb, is published in Nature Neuroscience.

  • Scientists studying the olfactory bulb, which transmits smell information from the nose to the brain, have found that separate circuits of neurons can independently control slow and fast signals within the same part of the brain. 
  • The work has implications for treating brain diseases, by improving understanding of how the wiring and function of this complex (and poorly understood) organ can go wrong in such diseases. 
  • The work, led by scientists, from the Medical Research Institute's National Institute for Medical Research, involved collaboration with researchers from the Max Planck Institute for Medical Research and the University of Heidelberg in Germany and the Massachusetts Institute of Technology in the USA.