Scientists have found a way to control the reward centre of the brain, using a miniature wireless device that emits light and causes the brain to release dopamine, the chemical associated with pleasure.
The technology could one day be used to deliver targeted therapies for common brain diseases, experts say.
The researchers developed miniature light-emitting diodes (LEDs) thinner than a human hair and transplanted them deep into the brains of mice. The rodents had been genetically altered so their brain cells could be activated and controlled by the light.
The study is a collaboration between neuroscientists from Washington University and engineers from the University of Illinois and is published today in the journal Science.
The researchers placed the genetically engineered and implanted mice in a maze, allowing them to roam. Each time the mice poked their nose into a particular hole in the maze, the system would wirelessly activate the LED to emit light. A signal would then be sent to the modified or responsive neurons to release dopamine.
The mice quickly learnt that poking their nose through the hole would give them a sense of pleasure and the animals tended to favour the part of the maze with the hole.
The researchers reported that the mice were not harmed from the implantation of the the devices, which used releasable injection needles.
Associate Professor Andrew Gundlach, neuroscientist and senior research fellow at The Florey Institute of Neuroscience and Mental Health, said the research was an incremental advance for the field of optogenetics, in which researchers use light to rapidly switch brain cells on and off to understand their function.
But he said the study broke new ground in the area of neuroengineering.
“The devices used in studies of brain circuits are getting smaller and smaller, despite in this case incorporating so many different capabilities in the one device, such as a built-in power supply, multiple light sources and even a temperature sensor, which is important to ensure the light emitted by the device isn’t ‘frying the tissue’,” he said.
Professor Gundlach said this kind of device could one day be used to deliver targeted therapies for common brain diseases.
“We already produce deep brain stimulation to correct symptoms in Parkinson’s disease and so some patients are already walking around with externally mounted devices and fairly invasive implants,” he said.
“What the researchers are saying is these very tiny multifunctional devices could be surgically implanted and would be driven to activate using wireless technology, whether that’s using radio frequencies or other, possibly biological, triggers.
"Experimentally, and in the long term if they do become useful in a therapeutic sense, they certainly offer a number of advantages over existing devices.”
Dr Mehdi Adibi, postdoctoral fellow at the John Curtin School of Medical Research at ANU, agreed that the technology held promise as a clinical device.
“The tiny size of the devices means they can even be used in humans without any worry about invasive operations or surgery or side effects of implanting bigger devices or reactions,” he said.
“And it’s more accurate because with these devices you can accurately and precisely stimulate neurons or record the activity of the neurons.”
The study authors say the research could also be used to identify and map brain circuits involved in complex behaviours such as sleep, depression, addiction and anxiety.
“Understanding which populations of neurons are involved in these complex behaviours may allow us to target specific brain cells that malfunction in depression, pain, addiction and other disorders,” said study co-author Michael R Bruchas, assistant professor of anaesthesiology at Washington University.
The next step in the team’s research is to manipulate the neural circuits involved in social behaviours to better understand what goes on in the brains of people with emotional or behavioural problems.