Slow and fast signals in same part of brain controlled independently

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 inNature Neuroscience.

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