Brain Computer Interfaces Explained
The history of BCI's, Utah array, neuralink and the future of humanity.
The human body is humming with electrical signals. Each thought, movement, and emotion results from an electrical signal transmitted throughout the nervous system. Imagine the possibilities if you could decipher these signals and write new ones directly to the brain. If everything from vision to locomotion is a symphony of neural activity, then by reading and writing to the brain and spinal cord, you could cure blindness and epilepsy. You could enable a paralyzed person to walk again or allow someone to communicate with a computer faster than they can talk. You could not only restore lost human abilities but also gain superhuman ones. Brain-Computer Interfaces represent an untapped reservoir of human potential, yet few people see it coming.
If you actually want to make use of these complex signals originating in the brain, you need to map the neural activity. You need to understand what the individual neurons are saying. To do this, you must have small sensors placed near individual neurons. The analogy goes as follows: trying to decode neural activity from sensors on the outside of the skull is like trying to understand how a factory works by listening from the outside. You might hear some vague sounds, but you will have no chance of understanding how the machinery works.
Non-Invasive Techniques
Electroencephalography (EEG) is a technique for extracting electrical signals from the brain by listening through electrodes on the outside of the skull. This can be very useful and can detect the cumulative signal produced by the billions of neurons in your cortex. Although it is not a precise measurement and cannot tell what individual neurons are saying, it can give a sense of the overall pattern of signals. This technique is useful but serves a different purpose than the implants we will look at next.
Why We Need Implants
Your brain contains billions of neurons, all interconnected and firing based on various stimuli and internal processes. Together, they create intricate networks of communication. These neural connections and patterns of activity underlie every thought, emotion, and action, shaping your perceptions, memories, and behaviors. This neural 'firing' is known as an action potential. When a certain threshold of signals is met within a neuron, it releases its charge, propagating an electrical impulse to connected neurons and the surrounding environment. Action potentials are typically measured between 50 to 500 μV (10^-6 volts) at around 300 to 10,000 Hz. Conversely, EEG signals range from 10 to 100 μV at 0.5 to 100 Hz. EEG readings are slower to change and not very powerful (1). The signal amplitude that can be read from an electrode placed near a neuron decreases rapidly as the distance between the electrode and the neuron increases, following a 1/r² relationship, where r is the distance between the neuron and the electrode (3). To record isolated signals from single neurons, electrodes typically need to be within 50-100 μm of the cell body (3). If you want to decode signals from a specific part of the brain and read from individual neurons, you must use small electrodes placed very close to the neurons.
The Utah array
The previous state-of-the-art BCI implant is the Utah Array, a device that has been used in humans since 2004. It has a 4.2x4.2 mm footprint with a grid of rigid electrodes. Each electrode is about the width of a human hair at the base (80 microns). The surgery to implant it is very invasive, requiring the grid to be manually positioned by a surgeon and pressed into the cortex with a pneumatic hammer. This often leads to relatively high tissue damage and scarring, as the electrodes are rigid and cannot avoid vasculature. The Utah Array supports between 96 and 128 electrodes, with multiple arrays used in tandem to support a maximum of 1,024 channels (4).
This implant initially protruded from the skull and was connected to a computer via a bulky port on top of the patient’s head. Despite its relatively low data rate and electrode resolution, the signals decoded from the device allowed recipients to control mechanical devices with their thoughts alone.
Neuralink - The New State of The Art
The Neuralink 'N1' implant contains 64 threads, each with 16 channels, totaling 1,024 electrodes. It is about the size of a quarter and sits flush with the skull. Each flexible electrode is approximately 5 microns in width, which is about 1/16th the width of a human hair. The surgery is performed by a robot, which automatically avoids vasculature and accounts for the natural movement of the brain. The implant is entirely wireless, leaving the patient looking exactly the same as before the surgery. Thanks to the tiny, flexible threads, the surgery can be performed without noticeable scarring or trauma. The processing ability of this implant is equally impressive. The first patient, Noland Arbaugh, participating in Neuralink’s first ‘Prime Study’ broke the world record for cursor control with 9 bps compared to the previous 4.6. Neuralink engineers using a mouse could only get around 10BPS. If you want to see how well you can do, you can find out here. Noland can use the implant to do anything you would use a computer for.
The Neuralink team will continue to iterate on this device. They intend to double the number of channels with the next iteration. The capacity of these new interfaces will keep increasing. The first product of Neuralink is called 'Telepathy,' which allows a human to control a computer with their mind. The second product, called 'Blindsight,' aims to restore vision to the blind. Even if their optic nerve is missing, Neuralink can stimulate the visual cortex to enable blind people to see again. The long-term goal of Neuralink is to connect humans to artificial intelligence so that we will not be left behind. Enabling high-bandwidth communication between humans and computers, as well as human-to-human communication, has incredible potential. Imagine talking with someone and feeling the exact emotion they feel. Imagine communicating a complex concept effortlessly, with no loss. Brain-Computer Interfaces could ultimately enable universal empathy among humans and unrestrained, instant communication between people and machines. This is a technology that can profoundly impact our lives, yet few people give it the credit it deserves.
In future posts, I will cover a few potential uses for BCIs, both in the short and long term. I will explore the science of the implant, the software that allows it to decode neural signals, and much more.
Sources:
Hong, Guosong, and Charles M Lieber. “Novel electrode technologies for neural recordings.” Nature reviews. Neuroscience vol. 20,6 (2019): 330-345. doi:10.1038/s41583-019-0140-6
“How the Utah Array is advancing BCI science” - Medical Design & Outsourcing
