Light can affect neurons, which can cause Alzheimer’s disease, epilepsy, and other disorders if they stop working.
The brain contains billions of neurons — tiny cells that use electrical impulses and chemical signals to communicate with one another and other parts of the body.
When neurons stop working properly, it can lead to brain disorders such as Alzheimer’s disease, epilepsy, or depression to develop.
To better understand and manage these disorders, scientists have been developing techniques of brain stimulation that allow them to influence neural activity.
In conventional methods of deep brain stimulation, electrical neurostimulators, or “brain pacemakers,” are surgically implanted in the brain.
As brain science continues to advance, researchers have been developing less invasive methods of stimulating cells deep within the brain.
While some experts have been using magnetic pulses or sound waves to stimulate neurons, researchers in the field of optogenetics have been using light.
“Dr. Chen and colleagues showed that near-infrared light, when used in combination with certain nanoparticles, allowed stimulation of neurons deep in the brain,” Dr. Karl Deisseroth, a professor of bioengineering and psychiatry and behavioral sciences at Stanford University, told Healthline.
“More work needs to be done to make this a robust and useful process,” he said, “but Dr. Chen and colleagues took a key step.”
Deisseroth is one of the leading pioneers of optogenetics, a technique in which brain cells are genetically engineered to respond to light.
In this method of brain stimulation, scientists transfer pieces of genetic code derived from algae and other microbes into the brain cells of mice or other animals. That genetic code causes neurons to produce light-responsive proteins, known as opsins.
When scientists expose opsin-producing neurons to certain wavelengths of visible-spectrum light, those neurons turn on or off.
By activating or suppressing specific neurons, researchers can learn more about the role those neurons play in brain function and brain disorders.
“In this way, the causal role and functional significance of cellular activity can be determined in any species or tissue or behavior of interest, ranging from memory to mood to movement,” Deisseroth said.
“Optogenetics brings unmatched capability for speaking the natural language of the brain, in terms of cell-type specificity and speed,” he added.
Opsin-producing neurons only respond to visible-spectrum light, which can’t penetrate deeply into brain tissue.
As a result, optogenetic stimulation has historically required the insertion of fiber-optic light sources inside the brain.
To develop a less invasive method of light delivery, Deisseroth and his colleague Polina Anikeeva, PhD, proposed the use of near-infrared (NIR) light.
NIR light can pass through the skull and deep into brain tissue, without the insertion of internal light sources. However, NIR light doesn’t trigger a response from opsin-producing neurons.
To harness the tissue-penetrating power of NIR light, Deisseroth and Anikeeva devised a patented method for coating opsin-producing neurons in tiny nanoparticles that convert NIR light into visible-spectrum light. This technique is known as NIR upconversion.
Chen and his research team applied this method, showing for the first time that NIR upconversion optogenetics can be used to control neurons deep in the brains of mice.
Chen’s research team used this technique to stimulate the release of dopamine in an area of the brain that’s believed to play a role in depression.
“Overcoming the challenge of optical penetration depth will be the key to realizing noninvasive remote optogenetics with high clinical translation potential,” Chen wrote in his prizewinning essay on the topic.
“Our recent study addressed this problem by applying a nanomaterial-assisted approach that ‘shifts’ the existing optogenetic tools into the near-infrared region,” he added.
While scientists continue to research optogenetics in mice, zebra fish, and other animals, it hasn’t been studied as a treatment for brain disorders in human subjects.
More work needs to be done to develop and test noninvasive methods of light delivery, as well as noninvasive strategies for transferring genetic code into brain cells.
“It is too soon to predict which technique will emerge at the forefront of next-generation noninvasive brain stimulation technology,” Chen said, in a press release issued by the American Association for the Advancement of Science.
“However, we believe that achievements such as NIR upconversion optogenetics are rapidly unlocking numerous development routes and paving the way towards a bright therapeutic future,” he continued.
In the meantime, other methods of noninvasive brain stimulation are also being developed, tested, and used in humans.
“There are noninvasive methods that don’t require gene therapies, such as transcranial magnetic and electrical stimulation, which are already used commonly with human subjects on an experimental basis,” Ed Boyden, PhD, a professor of neurotechnology at the Massachusetts Institute of Technology (MIT), told Healthline.
Transcranial magnetic stimulation (TMS) is a noninvasive procedure in which magnetic fields are used to stimulate nerve cells in the brain. The Food & Drug Administration (FDA) has already
Members of Boyden’s research group have also conducted research on transcranial electric stimulation (TES), a noninvasive approach to brain stimulation in which electrodes are placed on the scalp. They hope this technique will allow them to reach cells deep within the brain, with greater precision than TMS.