The human brain contains billions of neurons, and these are organised into thousands of distinct groups. For researchers, knowing the exact function of each type of neuron would be invaluable, as it would help them to find the root of many diseases and develop effective treatments.

Currently, scientists must gain their knowledge of neuron function by correlating brain activity with certain behaviors, for example linking a damaged area of the brain to a particular loss of function. They can also activate certain areas of the brain and study the resulting behaviour, but the methods available to do this are invasive, which greatly limits their use.

Investigators at Duke University and the University of North Carolina (UNC), US, have now developed a non-invasive technique that could potentially allow neuroscientists to discover the function of any population of neurons in an animal brain.

In a previous study, Dr Bryan Roth, at UNC, explored his idea to create a cell receptor that could somehow be incorporated into neurons, and which could only be activated by a specific inert drug. This receptor would act as a type of switch, activating a particular set of neurons in the brain.

Using yeast genetics, Roth and his team managed to create a receptor that could interact with a specific chemical. This was possible because yeast can reproduce and evolve very quickly.

The group set out to create a similar receptor in animal models. In their first attempt to breed animals possessing the receptor, they decided to target the neurons of the hippocampus and cortex. The receptor was designed to be activated by a drug called clozapine-N-oxide (CNO), which had no other effects on the animals, nor upon the neurons that did not contain the receptor.

Interestingly, when the animals were injected with CNO, they started to experience seizures. The researchers had created a model for studying epilepsy.

For the current study, Dr Roth collaborated with epilepsy expert Dr James McNamara, at Duke University. Their team discovered a method of selectively activating certain sets of neurons, using controlled administration of CNO. In this way they were able to examine neuronal activity before and during seizures.

Dr McNamara commented "Elaborating on this method promises to let scientists engineer different kinds of mutant models in which single groups of neurons will be activated by this chemical, so scientists can understand the behaviors mediated by each of these groups."

For epilepsy, the discovery of this method is extremely exciting. The knowledge gained from its future implementation could lead to better treatments for humans, which target only the precise neurons responsible for seizure development, and cause fewer side-effects.

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