Harvard Medical School researchers have developed implantable microcoils that allow highly specific stimulation of neurons using electromagnetic induction.
Neural stimulation has shown promise for the treatment of epilepsy, although researchers have struggled to develop a technique that allows the stimulation of single neurons or highly targeted groups. Implanted electrodes can deliver current that can stimulate multiple neurons, although the techniques developed so far lack specificity and can cause scarring, which reduces the effectiveness of the treatment as the scars block current from reaching neurons.
Some advances have been made that allow more targeted stimulation of neurons, although while the technologies have shown promise, incorporating them into implantable devices has proved difficult.
Transcranial magnetic stimulation has been shown to be effective when used on parts of the brain that regulate mood. The technique has been used to treat depression, but similarly, the technique lacks specificity. While microcoils could be used to generate fields to activate neurons in theory, the problem has been generating sufficiently strong fields.
However, Shelley Fried and his team at Harvard Medical School’s neural prosthetics lab believe they have developed implantable microcoils that can deliver current to activate neurons. The microcoils could be used to target very specific groups of neurons allowing physicians to stimulate neurons with considerable accuracy. The microcoils are small enough to be implanted – measuring just 100 micrometers wide – yet they can generate electromagnetic fields capable of activating specific neurons.
The implantable microcoils are constructed from silicon and include copper microwires that generate electromagnetic fields from their tips. The microcoils can be used to activate vertically oriented neurons, without activating horizontal branches.
Fried’s team demonstrated the technique in anaesthetized mice and were able to stimulate the motor cortex and cause whiskers to twitch. The team has produced similar responses to what is achievable with electrical stimulation, although the microcoils offer far greater accuracy. The researchers have suggested the microcoils could be used to stimulate specific areas of the visual cortex, something which electrical stimulation cannot be used for. The microcoils could therefore play a role in visual prosthetics. Fried also believes the microcoils could be used in brain-computer interface systems, which could potentially be used to control robotic limbs.
Further tests on animals will be conducted to see if the microcoils are effective at stimulating patches of neurons in monkey brains while the animals are awake, and lab tests will also be conducted on human brain tissue.