Deep brain stimulation (DBS) is a standard medical treatment where electrodes are placed in specific areas of the brain to help with conditions like Parkinson’s disease and obsessive-compulsive disorder. While it works well, the surgery can be complicated and risky, so it’s not always used.
New tiny magnetic discs offer a safer way to achieve similar effects.
Developed by MIT scientists, magnetic nanodiscs offer a less invasive way of stimulating parts of the brain. According to scientists, this could lead to stimulation therapies without implants or genetic modification.
These tiny discs are about 250 nanometers across (about 1/500 the width of a human hair). As scientists reported, they can be injected directly into the desired location in the brain. From there, they could be activated at any time simply by applying a magnetic field outside the body.
A new pathway for the stimulation of nerve cells within the body
The new particles could quickly find applications in biomedical research and eventually, after sufficient testing, might be used in clinical settings.
Scientists thought a unique magnetoelectric material could help stimulate the brain remotely using magnets. However, creating this tiny material was quite challenging. They synthesized new magnetoelectric nanodiscs and worked with Noah Kent, a postdoc with a physics background, to study their properties.
These nanodiscs have a two-layer design: a magnetic core and a piezoelectric shell. When magnetized, the magnetic core can change shape, creating strain in the piezoelectric shell. This strain generates electrical signals that can stimulate neurons when the nanodiscs are exposed to magnetic fields.
The shape of the discs is crucial to their effectiveness. Unlike previous attempts using round magnetic particles, these disc-shaped nanodiscs enhance the magnetoelectric effect by more than 1,000 times.
The researchers first tested the nanodiscs on cultured neurons, successfully activating them with short magnetic pulses without needing any genetic changes.
New magnetoelectric effect discovered
Next, they injected the nanodiscs into specific areas of mice brains. By turning on a nearby weak electromagnet, they could trigger the nanodiscs to release small electrical jolts in those brain areas. This stimulation could be easily controlled remotely by switching the electromagnet on and off.
The team discovered that the magnetoelectric nanodiscs could stimulate the ventral tegmental area, a deep brain region linked to feelings of reward. They also successfully stimulated the subthalamic nucleus, essential for motor control.
Kim explains, “This is the region where electrodes typically get implanted to manage Parkinson’s disease.”
The researchers successfully used the nanodiscs to modulate motor control. By injecting them into one side of the brain, they could make healthy mice rotate when a magnetic field was applied.
The nanodiscs triggered neuronal activity similar to traditional implanted electrodes, providing mild electrical stimulation. They achieved very precise stimulation timing and experienced much less foreign body response than with electrodes, potentially making deep brain stimulation safer.
The precise stimulation was due to the unique, multilayered chemical composition and the specific shape and size of the nanodiscs.
White matter affects how people respond to brain stimulation
Polina Anikeeva, a professor in MIT’s Departments of Materials Science and Engineering and Brain and Cognitive Sciences, said, “While the researchers successfully increased the magnetostrictive effect, the second part of the process, converting the magnetic effect into an electrical output, still needs more work. While the magnetic response was a thousand times greater, the conversion to an electric impulse was only four times greater than with conventional spherical particles.”
Kim said, “This massive enhancement of a thousand times didn’t completely translate into the magnetoelectric enhancement. That’s where a lot of the future work will be focused: on making sure that the thousand-times amplification in magnetostriction can be converted into a thousand-times amplification in the magnetoelectric coupling.”
Noah Kent, a postdoc in Anikeeva’s lab with a background in physics, said, “In terms of the way the particles’ shapes affect their magnetostriction, it was quite unexpected. It’s kind of a new thing that just appeared when we tried to figure out why these particles worked so well.”
Anikeeva adds: “Yes, it’s a record-breaking particle, but it’s not as record-breaking as it could be.”
Journal Reference:
- Kim, Y.J., Kent, N., Vargas Paniagua, E. et al. Magnetoelectric nanodiscs enable wireless transgene-free neuromodulation. Nat. Nanotechnol. (2024). DOI: 10.1038/s41565-024-01798-9
