Ultra-thin, high-res sensor records single-neuron activity deep in the brain
Researchers have used a novel manufacturing technique to create a minimally invasive, customizable sensor that can wirelessly record deep brain activity down to a resolution of one or two neurons. The device has potential applications in a wide range of neurological conditions such as treatment-resistant epilepsy, Parkinson’s disease, and chronic pain.
A gold standard approach used in a wide variety of neurological disorders, such as treatment-resistant epilepsy and Parkinson’s disease, is stereoelectroencephalography (SEEG), where implanted electrodes record brain activity and/or provide direct electrical stimulation to specific brain regions. However, many electrode arrays currently used in the clinical setting have limited spatial resolution and are unable to record from small, discrete neuronal populations, let alone single neurons.
Researchers led by a team from the Integrated Electronics and Biointerfaces Laboratory (IEBL) in the Jacobs School of Engineering at UC San Diego have upped the ante with a potentially game-changing brain sensor. Wireless, customizable, minimally invasive and a fraction of the width of a human hair, the device can provide high-resolution recordings from deep inside the brain as well as deliver therapeutic electrical stimulation.
“The new depth electrodes combine two unique features: the much higher resolution of recording contacts combined with stimulation capability, which would improve our ability to understand – and potentially treat/change – neural circuits in parts of the brain that are not accessible by surface or penetrating interface,” said study co-author Ahmed Raslan. “This new electrode is a platform neural interface that can both read and write into the brain in experimental and clinical environments; as such, the potential uses and applications are unlimited.”
The key to the micro-stereo-electroencephalography (µSEEG) device’s capabilities is its unique manufacturing process, derived from existing technologies used to make digital display screens. The probes are ‘monolithic’ – individual components are stacked on top of one another to create a single cohesive unit – removing the need to assemble additional wires to take recordings. It also means the probe is only 15 microns thick, which is about one-fifth the width of a human hair, and 1.2 mm wide. Their tiny size minimizes damage to brain tissue upon insertion and extraction.
“We developed an entirely different manufacturing method for the thin-film electrodes that can reach deep brain structures – at a depth that is necessary for therapeutic reasons – enabling reproducible, customizable, and high-throughput production of electrodes but with a high spatial resolution and channel count despite a thinner electrode body,” said Shadi Dayeh, corresponding author of the study. “Additionally, the electrode insertion is compatible with existing surgical techniques in the operating room, lowering the barrier for their adoption in clinical procedures.”
The researchers created µSEEGs of different lengths for use in small and large animals and humans: a 32-electrode version with a recording length of 1.92 mm, a 3.8 mm 64-electrode version, and a 7.65 mm 128-electrode version for accessing deeper brain structures. Testing their devices in rat, pig, and non-human primate brains over the short and long term and at different depths, they found it could record at a depth of 10 cm (4 in), including recording the activity of single and multiple neurons.
The µSEEG was also tested on two patients scheduled for surgery to remove a brain tumor. During the surgery, the researchers inserted their device into the brain tissue about to be excised. Although the recordings were short – 10 minutes – the device picked up ongoing spontaneous neural activity. Conventional SEEGs generally have between eight and 16 electrodes. While their larger device has 128, the researchers plan to expand that number to thousands, dramatically enhancing the ability of clinicians to obtain and analyze brain signals at a higher resolution.
The researchers say the new tech will be particularly useful for epileptic patients undergoing monitoring for seizure activity.
“Currently, [epileptic] patients who undergo this type of evaluation remain in hospital for the duration of the study, where we try to capture where their unique seizures originate during a period of time that typically lasts from 7-21 days,” said Sharona Ben-Haim, a study co-author. “During this time, patients are tethered to their hospital beds by the wired cords from the current clinical electrode system. This new technology has the capacity to potentially allow us to send these patients home, freeing them from a long hospital stay and potentially allowing us to record for longer periods of time and obtain more robust information to help us ultimately treat their seizures with more precision and resolution than previously possible.”-
While the published study reports brain-recording data only, the µSEEG also includes 16 stimulation contacts designed to provide electrical stimulation to precise locations in the brain. The researchers are currently using their scalable, thin-film manufacturing approach to develop a brain-computer interface that records brain activity and delivers therapeutic electrical stimulation.
Beyond treatment-resistant epilepsy, the researchers say the µSEEG has a broad range of potential applications, including helping people with Parkinson’s disease, movement disorders, OCD, obesity, treatment-resistant depression, and chronic pain.
“There is no question in my mind that this will help us understand both normal brain function and pathology much better and will lead to new ways to help people suffering from epilepsy and a variety of other neurological conditions,” said Sydney Cash, a study co-author.
The study was published in the journal Nature Communications, and the video below, produced by the Jacobs School of Engineering, explains how the µSEEG is made and used.
Source: UC San Diego