#### Sources - <iframe width="560" height="315" src="https://www.youtube.com/embed/rzNOuJIzk2E" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe> - https://neuralink.com/blog/monkey-mindpong/ - https://www.biorxiv.org/content/10.1101/703801v4.full - <iframe width="560" height="315" src="https://www.youtube.com/embed/CkUcCcRq_eM" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe> #### The device - **Wireless, implantable device with 1024 recording channels** (256 electrodes with 16 contact pointx each) - Order of magnitude better than the current state of the art (Utah array with 100 electrodes) - Li-ion battery that's wirelessly recharged from induction charging - **Neural spike detection on the device itself** as transmission rate has to be reduced for saving power - Amplifiers have to be on the device itself - "This recording stack must amplify small neural signals (<10 μVRMS) while rejecting out-of-band noise, sample and digitize the amplified signals, and stream out the results for real-time processing—all using minimal power and size." - **Aggregates spikes measured every 25 ms and sends it for 1024 electrodes** - "While most electrophysiologists spike-sort data offline and spend significant effort to reject false-positive spike events, BMI events must be detected in real time and spike detection parameters must maximize decoding efficacy. Using our custom online spike-detection software, we found that a permissive filter that allows an estimated false positive rate of ~0.2 Hz performs better than setting stringent thresholds that may reject real spikes (data not shown)." - Sends over bluetooth - "The density of recording channels necessitates placing the signal amplification and digitization stack within the array assembly, otherwise the cable and connector requirements would be prohibitive." - **Material used for electrodes**: polyamide coating on gold - "The main substrate and dielectric used in these probes is polyimide, which encapsulates a gold thin film trace" - **Multiple devices per brain can be implanted:** - In a larger brain, multiple devices with this architecture could be readily implanted, and we could therefore interface with many more neurons without extensive re-engineering. - **The device itself integrates with skull,** but that has severe issues - See https://www.reddit.com/r/Neuralink/comments/n5meqp/how_will_neuralink_stay_in_place_in_your_skull/ - **Robotic insertion enables really fast surgical implantation** - So the person can go to get surgery in a procedure that takes a few hours and comes back home the same day - "the total insertion time for this study averaged ~45 min, for an approximate insertion rate of 29.6 electrodes per minute" - Brain is pulsating so precision insertion can only happen though 3d optical mapping of brain and robotic insertion ![[Screenshot 2021-12-03 at 1.04.05 PM.png]] The vasculature of the brain requires thread-like electrodes to be inserted precisely so they don't touch the blood vessels ans trigger an immune response Potential ways to prevent immune response: - Coat electrodes in proteins? - Administer antibiotics at the time of surgery - Avoid blood vessles Issues with existing microelectrodes: they're large and stiff, hence generate immune response. - "While rigid metal arrays facilitate penetrating the brain, the size, Young’s modulus and bending stiffness mismatches between stiff probes and brain tissue can drive immune responses that limit the function and longevity of these devices" #### Challenges - **Avoiding scarring of the electrodes** by glial cells that erode functionality - ""If you look at implanted electronics in the brain over the past 10 to 20 years, all suffer from a common problem which is the implant's electronic probes ... create scarring in brain tissue," (via [here](https://www.businessinsider.in/science/this-one-big-problem-is-why-we-cant-control-computers-with-our-brains-yet/articleshow/47684092.cms)) - "When the body senses an implant made of material that triggers the body's immune system, glial cells begin to create scar tissue around it to protect the brain from what it considers a foreign body. When a probe becomes too engulfed in glial scarring, it loses functionality." - **Readout possible only from thousands of neurons** (not tens of them, which may be required for actual precise control) - "Essentially, we have okay-ish knowledge of large-scale phenomena (~1cm3) and small-scale (synapse, nucleus) behavior, but the middle ground (10's of neurons) is quite hard. Unfortunately, that seems to be were all the magic happens." (via [here](https://news.ycombinator.com/item?id=26739872)) - **Immune response** - Making the device biocompatible (no immune reaction) and corrosion resistant (from brain fluids and salts) - **Infections** - How to do you ensure no infections happen during or after the surgery - **Inflammation** - How do you ensure there's no inflammation which is is common for surgeries - **Complicated surgery required** - they use a robot as the threads of the electrode are very fine - "Each thread can be individually inserted into the brain with micron precision for avoidance of surface vasculature and targeting specific brain regions." - **Minimize displacement of electrodes in the brain** - One goal of this approach is to maintain a small thread cross-sectional area to minimize tissue displacement in the brain - The electrodes inside the brain could move causing the need to do recalibration again and again and possibly repeated damage to the brain - **Impedence** - As electric currents are anyway small, any impedence will cause loss of signal - **Avoiding touching blood vessels inside the brain** - "damage to the blood-brain barrier is thought to play a key role in the brain’s inflammatory response to foreign objects" - **Lack of humanity's neuroscience knowledge** - Is electrical activity the only or even major component of brain dynamics? - "For instance, astrocytes/glia are still quite understudied despite being ~1/2 of the cells in your brain (maybe). Mostly, this is because they are not very electrically reactive. But they are known to be a pathway for NMDAr recycling as well as surrounding the synapse in certain parts of the brain. This issue of astrocytes is one of thousands that we're still trying to get a grip on." (via [here](https://news.ycombinator.com/item?id=26739872)) #### First application enable people with paralysis to navigate the web and text. They want to break the world record in BCI based typing (where current record is as per this [paper](https://stacks.stanford.edu/file/druid:jx921pv3255/TechnicalReport01_GPT_BCIs-2021-05-20.pdf)) <iframe class="signup-iframe" src="https://invertedpassion.com/signup-collector" title="Signup collector"></iframe>