Cortical stimulation has been shown to be useful as a non-pharmacological therapeutic strategy for the treatment of many diseases like Epilepsy, Parkinson’s, Dystonia, and Chronic Pain among others. One of the most studied and translated approaches is the Deep Brain Stimulation (DBS), which involves the implantation of electrodes in particular regions of the brain to deliver electrical pulses. This therapeutic application is hypothesized to modulate the dysfunctional neural signaling and restore the previous function. The approach involves implantation of an electrode through the skull, and despite the success, there are risks associated. Risk of infection, cerebrospinal leakage and a 2-3 percent patients showing an increased risk for hemorrhage which leads to other debilitating side effects are some of the common contraindications. Can we achieve implant electrodes in minimally invasive procedures?
Brain Stentrode, a brain interfacing electrode that is implanted within a blood vessel was developed by a team of researchers from The Royal Melbourne Hospital, The University of Melbourne and the Florey Institute of Neuroscience and Mental Health. They have tested the electrode for recording neural activity, and the work was published in Nature Biotechnology in 2016. Principal author and Neurologist at The Royal Melbourne Hospital and Research Fellow at The Florey Institute of Neurosciences and the University of Melbourne, Dr. Thomas Oxley, said the Stentrode was revolutionary.
Co-principal investigator and biomedical engineer at the University of Melbourne, Dr. Nicholas Opie, said the concept was similar to an implantable cardiac pacemaker—electrical interaction with tissue using sensors inserted into a vein, but inside the brain.
"Utilizing stent technology, our electrode array self-expands to stick to the inside wall of a vein, enabling us to record local brain activity. By extracting the recorded neural signals, we can use these as commands to control wheelchairs, exoskeletons, prosthetic limbs or computers," Dr. Opie said. Video below shows the Stentrode in action.
Building on this success, Dr. Opie’s work published on Dec 3rd, 2018 in Nature Biomedical Engineering, addresses the possibility of using the Stentrode for delivering clinically relevant chronic selective cortical stimulation. This study involved researchers from The University of Melbourne, Florey Institute of Neuroscience and Mental Health, The Royal Melbourne Hospital, Monash University and the company Synchron Australia.
The study involved implantation of 4mm Stentrode in the superior sagittal sinus(SSS), a blood vessel overlying the motor cortex in eight sheep with a total of 67 viable electrodes. Stimulation of over 58% electrodes resulted in motor responses when electrically activated.
“The electrodes were positioned along the Stentrode, adjacent to different regions of the brain. By delivering current through these electrodes, we were able to stimulate different brain regions and observe different responses.”
The authors also compared the efficacy of Stentrodes directly with the implantable cortical surface and penetrating electrodes. "Stimulation-induced responses of the facial muscles and limbs were observed, and were comparable to those obtained with electrodes implanted following invasive surgery," the researchers wrote.
"A minimally invasive endovascular surgical approach utilizing a stent-electrode array is an encouraging safe and efficacious way to stimulate focal regions of the brain."
"By adding the ability to speak to the brain using electrical stimulation, we have created a two-way digital communication device," Dr. Opie said. "In one application, the Stentrode could be used as a tool to record the onset of an epileptic seizure, and provide stimulation to prevent it."
Co-author Dr. Sam John said it was the first time such an implant was able to stimulate the brain without needing to perform open brain surgery. He said this work opened the way to making treatment for drug-resistant neurological conditions accessible to a greater number of people.
"This offers hope of less invasive treatments for the symptoms of conditions such as Parkinson's disease, epilepsy, depression, and obsessive-compulsive disorder," he said.
Their next step is to investigate the parameters for stimulation, to discover the lowest possible current the device requires and make it as safe as possible, before progressing to human trials.
“We have a lot of work to do in fine-tuning the parameters,” says Dr. Opie. “And these will vary depending on how the device is being used.”
"From within a blood vessel in the head, the Stentrode can pick up brain signals when people think about moving," Dr. Opie said. "These can be converted into commands that enable direct-brain control of computers, vehicles or prosthetic limbs. With stimulation, sensory feedback is possible, and people may be able to feel what they are touching."
“I am excited to see our technology enhance the quality of someone’s life,” says Dr. Opie.