In this blog post, we’ll explore the principles, use cases, technical limitations, and ethical issues surrounding brain-computer interface (BCI) technology that uses brainwaves.
What if you lost both legs in an unexpected accident? Not only would activities like riding a bicycle or playing soccer become difficult, but even something as ordinary as running to the convenience store down the street could become a challenging and dangerous task. Everyday activities that were once taken for granted—such as taking a walk in a nearby park on the weekend—would become nearly impossible.
However, technological advancements are offering new hope to people facing these challenges. Do you remember the scene in the movie ‘Avatar’ where Jake, a Marine who had lost the use of his legs, was able to move freely again by connecting to a Na’vi avatar? One of the technologies frequently cited as the inspiration for that scene is the brain-computer interface (BCI). BCI technology is gaining attention as a means of offering new possibilities to people whose physical functions have been impaired or lost due to various causes.
According to the World Health Organization (WHO) and various international health statistics, there are a vast number of people worldwide suffering from various neurological disorders, including motor and sensory impairments, and the population with visual impairments also numbers in the hundreds of millions. For these individuals, BCI technology is regarded as more than just cutting-edge technology; it is seen as a vital alternative that can improve their quality of life. So, how does BCI technology work to replace or supplement impaired physical functions?
Many physical impairments are often irreversible. Once normal bodily functions are damaged, it is difficult to fully restore them. This is particularly true for the loss of body parts or damage to vision, hearing, and neurological functions. Consequently, people with such disabilities often have to live with these challenges for a long time. While stem cell therapy has also generated high expectations, it has not been able to resolve all issues due to technical limitations, ethical debates, and difficulties in clinical application. In contrast, BCI technology can be utilized with the patient’s consent, and its potential for continued development is widely recognized, given that accessibility is gradually improving alongside advancements in medical devices and information technology. So, how exactly can BCI technology replace or assist impaired bodily functions?
Research into BCI technology began when German psychiatrist Hans Berger succeeded in measuring electrical signals generated by the human brain. Subsequently, researchers discovered that brainwaves take on different patterns depending on a person’s thoughts, behaviors, and emotions, and suggested that by utilizing these characteristics, it might be possible to partially replicate the way the brain controls the body and processes sensory information. Based on this research, full-scale studies aimed at restoring vision, hearing, and motor functions began in the 1970s, and BCI technology has since evolved rapidly alongside advancements in electrode technology, signal processing, and AI-based analysis. Furthermore, as EEG waves were classified into alpha, beta, gamma, theta, and delta waves, and their respective characteristics were understood, it became possible to interface with various external devices. Currently, some implantable electrode-based BCI technologies are being utilized in clinical research and the medical field to support the restoration of vision, hearing, motor function, and tactile sensation, albeit to a limited extent.
BCI technology connects the brain to external devices to exchange information. It is also known as a Brain-Machine Interface (BMI) or Direct Neural Interface (DNI). By utilizing electrical signals generated by the brain, it assists in controlling the body or perceiving the external environment, and serves to replace or supplement impaired bodily functions through mechanical devices. This technology is broadly classified into invasive BCI and non-invasive BCI, depending on the method used to acquire signals. Invasive BCI involves inserting electrodes directly into the cerebral cortex to measure brain signals, while non-invasive BCI uses sensors attached to the scalp to measure brainwaves.
The invasive method involves inserting electrodes directly into the cerebral cortex to transmit signals generated by the brain to external devices or bodily organs. Conversely, it can also transmit electrical signals generated externally to the brain, helping it perceive information that it would not normally be able to process. Because this method allows for the transmission of highly precise signals, it is primarily being researched in fields requiring advanced information processing, such as vision, hearing, and motor functions. For example, this includes technologies that convert visual information captured by a camera into electrical signals and transmit them to the brain, or that transmit signals generated by the brain to prosthetic arms or legs to move them according to the user’s intent.
For instance, in the case of patients who have lost their vision due to damage to the retina or optic nerve, research is underway on a method that converts images captured by a camera into electrical signals—including color and contrast information—and transmits them to the brain. This approach works on the principle that electronic devices partially take over the functions that would normally be performed by the eyes and optic nerves, thereby helping the brain perceive the surrounding environment.
Due to its advantages—high accuracy and sensitivity, as well as relatively low susceptibility to external noise—the electrode implantation method continues to be utilized as a key technology in research aimed at restoring physical functions. In fields where malfunctions can directly lead to safety issues—such as research on naturally moving robotic arms, implementing tactile feedback, or assisting patients with spinal cord injuries in walking—extremely high reliability is required. Therefore, the implantable electrode method is typically chosen. However, since this method requires the direct implantation of electrodes into the brain, it necessitates surgery and carries various risks, including infection, tissue damage, and long-term biocompatibility issues. There is also a possibility that signal quality may deteriorate over time due to changes in the tissue surrounding the electrodes.
The EEG-based method involves attaching electrodes to the scalp to measure brainwaves, detecting the subtle electrical signals transmitted through the scalp, amplifying them, and using them as control signals. While it is similar to the electrode-implantation method in that it converts brain activity into electrical signals for use, the method of signal acquisition differs. While the electrode-implanted method directly measures electrical signals generated within the brain, the EEG-based method detects and collects signals transmitted through the skull and scalp before analyzing them. The user’s intent is determined by analyzing the EEG data accumulated over a certain period of time.
For example, let’s assume that a specific EEG pattern repeatedly appears when a user thinks, “I want to shoot a bow.” The system learns these EEG patterns in advance; subsequently, when a similar pattern is detected, it recognizes it as a command to “shoot a bow” and instructs the computer to perform the corresponding action. Generally, this method works by extracting average characteristics from EEG data collected over a certain period and then comparing them with subsequently measured EEG signals; if a similarity above a certain threshold is confirmed, the system interprets it as the corresponding command.
Unlike methods that require electrode implantation, this approach does not necessitate separate surgery. Furthermore, since EEG (Electroencephalography) equipment for measuring brainwaves is widely used in the medical field, it is relatively affordable and highly accessible. In the past, there was the inconvenience of having to use conductive gel between the electrodes and the scalp to improve measurement accuracy; however, user convenience has greatly improved with the recent development of dry EEG electrodes that can reliably measure signals without gel. However, compared to the implantable electrode method, signal accuracy and sensitivity are lower, which limits its ability to replicate complex sensations or precise movements; there is also a possibility of malfunction due to interference from external electrical signals or physical movement. Furthermore, because the skull attenuates the signals, it is difficult to accurately measure high-frequency components, and there is a limitation in that only signals originating primarily from the cerebral surface can be analyzed.
Examples of BCI technology being put to practical use can already be found in various fields. A prime example is physicist Stephen Hawking, who suffered from amyotrophic lateral sclerosis (ALS) and continued his research and lectures using a computer and a speech synthesis device. However, although the original text directly cites this as an example of BCI technology, the primary communication device Dr. Hawking actually used was an input device that detected facial muscle movements, and it is not generally classified as a BCI system. Therefore, it is more appropriate to understand this case as a representative example of assistive communication technology.
On the other hand, implantable BCI technology is actively being utilized in research such as using brain signals to move robotic arms to pick up objects or drink beverages, helping patients with spinal cord injuries attempt to walk, and stimulating the brain to restore visual function. Since these applications require complex movements or precise control—and thus demand high accuracy—they mostly rely on implantable electrode systems.
As such, BCI technology is recognized as a crucial technology for improving people’s quality of life. However, there are also perspectives that raise concerns about this technology. Even based solely on the scientific facts uncovered to date, the human brain possesses an extremely complex structure, and we do not yet fully understand the connections between neurons or the processes of information transmission. Therefore, accurately interpreting the vast amount of signals generated by the brain to the extent that they can be freely utilized in daily life remains a very difficult challenge. Furthermore, because the signals measured from the scalp in non-invasive BCIs are very weak, they are easily affected by electrical interference or noise from the surrounding environment, which can reduce accuracy. Ultimately, there is a limitation in that the electrode-implantation method is often still preferable in fields that require high reliability and stability.
Furthermore, BCI technology raises ethical concerns. The process of directly connecting the human brain to machines has sparked various ethical debates, including the protection of personal information and brain signals, the risk of hacking, human autonomy and identity, and inequalities in access to technology. While it is sometimes regarded as posing relatively fewer ethical burdens than stem cell technology, it is difficult to view it as a technology completely free from ethical issues.
To address these issues, research on partially invasive BCIs (Partially Invasive BCI) has been actively conducted recently. This method measures signals by placing electrodes beneath or on the surface of the skull, rather than inserting them inside the skull. It offers the advantages of higher signal strength and accuracy compared to non-invasive methods, while reducing the surgical burden and postoperative complications associated with electrode implantation. Therefore, it is regarded as a technology that strikes a balance between the two approaches, as it allows users to control devices requiring relatively complex movements while enhancing safety by avoiding the direct insertion of electrodes into brain tissue.
Despite the various controversies and technical limitations discussed so far, BCI technology continues to generate high expectations as a means of providing new freedom to many people. In fact, various clinical studies are ongoing in medical settings to restore motor functions, support communication, and partially compensate for sensory impairments. For people who must live with lifelong disabilities, helping them regain the freedom to drink water on their own, enabling them to express themselves, and supporting the partial recovery of lost sensations goes beyond mere technological advancement—it holds significant meaning in improving the quality of human life.
Of course, the goal of alleviating human suffering alone does not solve every problem. As technology advances, safety verification must become even more rigorous, and social discussions—such as the protection of personal and brain data, the establishment of ethical standards, and ensuring equitable access to technology—must also evolve alongside it. For BCI technology to truly become a technology for the benefit of humanity, it must be supported not only by outstanding technical expertise but also by responsible research and social consensus.
Nevertheless, countless researchers and medical professionals are continuing their research tirelessly to overcome these challenges. Since the purpose of this technology is to make people’s lives freer and more fulfilling, BCI technology is expected to continue advancing by addressing technical limitations and ethical challenges one by one.
And, as a line from a certain movie goes, we will eventually find the answer. Just as we always have.
