Fine-grained brain stimulation can be achieved through the use of flexible nanoelectrodes.

Traditional implantable medical devices designed to stimulate the brain are often too stiff and bulky for what is considered to be the body’s softest tissue.

To address this problem, Rice University engineers have developed minimally invasive, ultra-flexible nanoelectrodes that can serve as an implantable platform for administering long-term, high-precision stimulation therapy.

According to a study published in Cell ReportsIn rodents, small, implantable devices formed stable, long-lasting, and smooth tissue-electrode interfaces with minimal scarring or deterioration. The devices delivered electrical pulses that matched nerve signal patterns and amplitudes more closely than stimuli did from conventional intracortical electrodes.

The high biocompatibility of the devices and the precise control of temporal and spatial stimulation could enable the development of novel brain stimulation therapies such as neural prostheses for patients with impaired sensory or motor functions.

“This paper uses imaging, behavioral, and tissue techniques to show how these tissue-embedded electrodes improve stimulation efficacy,” said Lan Luan, assistant professor of electrical and computer engineering and corresponding author on the study. “Our electrode delivers tiny electrical pulses to trigger neural activity in a very controlled way.

“We were able to reduce the current necessary to elicit neuronal activation by more than an order of magnitude. The pulses can be as minute as a few hundred microseconds in duration and one or two microamps in amplitude.”

The new electrode design developed by researchers at the Rice Neuroengineering Initiative represents a significant improvement over traditional implantable electrodes used to treat conditions such as Parkinson’s disease, epilepsy and obsessive-compulsive disorder, which can cause adverse tissue reactions and unintended changes in neural activity.

“Conventional electrodes are very invasive,” said Zhong Shih, associate professor of electrical and computer engineering and corresponding author of the study. “They recruit thousands or even millions of neurons at once.”

“Each of these neurons is supposed to have its own tones and coordinate in a certain pattern. But when you shock them all at the same time, you basically disrupt their function. And in some cases it works for you and it has the desired therapeutic effect. But if you want, for example For example, to encode sensory information, you need greater control over the stimuli.”

Xie likens stimulation via conventional electrodes to the disruptive effect of “blowing an air horn in everyone’s ear or hearing a loudspeaker blast” in a room full of people.

“We used to have a very big megaphone, and now everyone has an earphone,” he said.

The ability to adjust the frequency, duration and intensity of the signals could enable the development of new sensory prostheses.

“The activation of neurons is more spread out if you use a larger current,” Luan said. “We were able to reduce the current and showed that we had a more focused activation. This could translate to higher fidelity stimulation devices.”

Luan and Xie are core members of the Rice Neuroengineering Initiative and their labs are also collaborating on developing an implantable optical prosthesis for blind patients.

“Imagine one day being able to implant electrode arrays to restore impaired sensory function: The more focused and deliberate the activation of neurons, the more subtle the sensation they generate,” Luan said.

An earlier iteration of the devices was used to record brain activity.

“We have a series of publications showing that this intimate tissue integration enabled by the ultra-flexible design of our electrode really improves our ability to record brain activity for longer periods and with better signal-to-noise ratios,” said Luan, who was promoted to become an associate. The professor is in effect from July 1.