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.