Closed-Loop Neurotechnologies

Closed-Loop Neurotechnology

Understanding the brain and other areas of the nervous system has always been challenging. While research has led to a better understanding at the cellular/neuron level, a clear picture of how those neurons work together as part of a larger system of neural circuits has been more evasive. 

Closed-loop neurotechnologies, an expanding area of study, are advancing the reading and writing of activity in the nervous system. This not only opens the door to a better understanding of whole brain function but also the possibility of better treatments for neurological conditions and better neural enhancement technologies. 

Types of closed-loop neurotechnologies

Bidirectional closed-loop neurotechnologies are devices that use a neural interface to read and write information to and from the nervous system. The act of reading is a type of decoding and involves interpreting brain and nervous system signals with electrodes or other sensors that pick up the electrical impulses that neurons send. 

Encoding works in the opposite direction, sending stimulus pulses into parts of the brain in order to affect a response. These processes form the so-called “closed loop.” Bidirectional devices can take on many different forms and come with a variety of specialized features as described below.

The neurotechnology landscape

Researchers break down neurotechnology into three primary categories of devices, as follows:

  • Neuromodulation technology: This category includes any devices that use a neural interface to stimulate some part of the peripheral, central, or autonomic nervous system. This type of technology can be open loop (only offering stimulation without receiving feedback) or closed loop (the stimulation parameters can be modified based on feedback responses). One application of this type of technology is neuromodulation therapy for patients with Parkinson’s disease, where sensors detect tremors, then provide appropriate stimulation to minimize or alleviate them.
  • Neuroprostheses technology: A neuroprosthesis is any device that provides a substitute for lost sensory, motor, or cognitive functions. These devices may target either the peripheral or central nervous system. And a common example of such a device is a cochlear implant, which allows people with hearing loss to interpret sounds through the stimulation of auditory neurons in the brain stem.
  • Brain-machine interfaces (BMIs): These are devices that create a direct connection between the brain and an external device (the “machine”). Some of these interfaces are unidirectional, allowing users to control an external device or receive sensory input from an external device. Others are bidirectional, allowing for both encoding and decoding to occur.

Features of closed-loop devices

Closed-loop devices vary in their invasiveness. They can include devices used outside the nervous system with no surgical intervention, as well as devices placed intracranially or within parts of the peripheral nervous system. These devices may involve the use of electric, magnetic, acoustic, or optical signals.

A noninvasive example would be the use of electroencephalogram (EEG) triggered transcranial magnetic stimulation (TMS). In this example, externally applied electrodes decode brain signals, and encoding occurs via external manipulation of magnetic fields over a certain brain region or regions. 

On the invasive end of the spectrum, deep brain stimulation (DBS) provides one of the most effective treatments for neurodegenerative diseases such as Parkinson’s disease and epilepsy. It requires placing electrodes directly into certain regions of the brain in order to provide electrical stimulation to those brain regions, as well as receive signals. The field of nanotechnology plays a role in the development of such devices because the goal is to maximize their efficacy while minimizing potential damage to neural tissue in placing the devices.

A newer and potentially less invasive alternative to closed-loop DBS devices is a technique called optogenetics, which provides a way to control neural activity with light and genetic engineering. By harnessing genetically encoded light-gated ion channels, researchers are able to optically stimulate target neurons. While this can also require insertion of optical fibers, in development are less invasive techniques, which involve using near-infrared light that penetrates biological tissue more easily without being scattered. 

Benefits of closed-loop neurotechnology

A multitude of benefits are possible with closed-loop devices. Among them are the following:

  • The ability to better treat neurological diseases and traumatic brain injury
  • The ability to compensate for nervous system or spinal cord injury
  • The ability to restore and improve memory and memory consolidation
  • Improved treatment and outcomes for mental health conditions
  • An increased understanding of how the brain works as a system

Advances in closed-loop neurotechnologies

The development of closed-loop devices is relatively new. Much prior research focused on open-loop devices that could either interpret signals or apply stimulation, but not both. Exploration into the creation of integrated devices with complete feedback loops that can self-regulate is a highly emergent field.

History of neurotechnology

The history of neuroscience and neurotechnology goes back thousands of years. The first written records of trauma to the nervous system trace back to an Egyptian papyrus from around 1700 BC. Over the centuries as science evolved, so too did the human understanding of the brain and nervous system. The 1800s and 1900s in particular were fruitful times for the fields of neuroscience, psychology, psychiatry, and cognitive science.

The computer age ushered in an era of more detailed understanding, particularly from 1990 (which US President George Bush declared as the start of the “decade of the brain”) to the present due to advanced technologies such as functional magnetic resonance imaging (fMRI), which allowed for functional brain modeling, and microchips and nanotechnology, which made many early DBS therapy interventions and neuroprostheses possible.

In 2013, the Obama administration announced the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative in an effort to develop technology enabling a deeper understanding of the brain. In alliance with the BRAIN Initiative, IEEE Brain’s mission is to facilitate cross-disciplinary collaboration and coordination to advance research, standardization, and development of neuroscience technologies to help improve the human condition.

Current trends

Therapeutic applications are a primary force behind much of current closed-loop neurotechnology development. This field holds significant promise in the treatment of movement disorders, spinal cord injuries, neurological diseases, chronic pain, and psychiatric disorders. 

Stakeholders in this technology responsible for driving current trends include the following:

  • Researchers and developers, who are responsible for the development of this technology
  • Academic institutions and science foundations, who are responsible for supporting the research
  • The device industry, which builds the devices that the researchers design
  • Component manufacturers, who are often responsible for the smaller and more advanced components used in the devices
  • Computational software developers, who develop the algorithms and programming required for closed-loop devices
  • Health-care providers and clinicians, who may wish to use these interventions with a patient
  • Health-care insurance providers, who need to weigh the pros, cons, and costs of these interventions relative to other treatments
  • Users and patients whom this technology is designed to aid
  • Pharmaceutical companies, for which this technology may be a competitor or a potential avenue for investment into cotherapies
  • Government entities and funding agencies that provide the majority of funding for the development of these technologies
  • Regulatory bodies that are responsible for ensuring the ethical use of these technologies

Next-generation closed-loop neurotechnology development and applications

As researchers develop these technologies, there is a strong drive toward decreasing invasiveness by using more advanced techniques and smaller or externally located devices. Coordinating closed-loop devices with artificial intelligence and machine learning can improve device efficacy and fine-tuning capabilities. But this further requires the ability to handle large amounts of data, making cloud computing capabilities viable for inclusion as well.

The future holds promise for generalized bidirectional devices with multiple different inputs and outputs operating autonomously. This goal is achieved in phases:

  • Phase 1: Improve sensor capabilities for feedback and increase understanding of downstream effects.
  • Phase 2: Improve targeting of stimulation technologies on both a spatial and temporal level.
  • Phase 3: Work toward increased adaptivity of closed-loop systems so that they self-adjust and improve.

Potential future applications include personalized treatment based on electrical signals and molecular physiologyfor example, closed-loop bladder control in paralyzed patientsas well as treatment of complex psychological problems such as addiction, anxiety, and schizophrenia. 

In addition to therapeutic applications, researchers are also exploring uses in the realm of augmentation. This includes things such as memory enhancement or learning enhancement, physical enhancements in the realm of military and defense, and consumer applications in the areas of wellness and entertainment. 

The future of closed-loop neurotechnology

As researchers develop a road map for closed-loop neurotechnology, there are many dimensions they must consider. The technology dimension involves considerations of what is possible and what challenges exist in designing the devices, the marketing dimension involves considerations as to how this technology can become widely available, and the ethical dimension examines associated moral principles.

Design challenges

The development of closed-loop neurotechnology requires overcoming several challenges. First, there is consideration of general design requirements, which include the ability to function in minimally invasive ways, provide intuitive interfaces, and be physiologically compatible as well as safe. 

Additional technological challenges include the following:

  • The need to scale devices down in size in order to minimize invasiveness, while maintaining effectiveness and robustness
  • Access to or design of materials that are stretchable, soft, and stable enough to remain viable when used within the body
  • Standardization and miniaturization of electrodes and sensors
  • The need to improve recording of signals, optimizing for processing speed and stability while minimizing noise
  • Support at scale for computation capabilities so that devices can effectively utilize artificial intelligence and machine learning 
  • Devices robust enough to withstand the environment of the human body, ideally for the person’s lifetime
  • Optimizing device power sources to prolong battery life
  • The need to improve wireless communication capabilities for better integration between external sensors and devices and internal ones
  • Reliable system validation to improve the safety and reliability of devices

Technology enablers and solutions

The development, design, and dissemination of these devices require a lot of moving parts working together. The research itself requires funding, the components needed to build the devices require manufacturing and standardization, the medical community must see a realistic benefit to the devices over current treatments, investment in manufacturing is needed in order to allow for standardization and wide availability, and so on.

The more this technology moves forward, the lower the barriers of entry for consumers should become. This is especially true as devices become less invasive, incurring decreased risk and increased ease of implementation. Initial clinical trials will also allow for advancement before a financial justification and funding system develops. 

As the fields of technology and electronics design advance, this again opens doors for further development of closed-loop neurotechnologies. Smaller, softer, stretchable, and lower-power electrodes and sensors are what will make these devices viable in the long term. 

Over time, the increase in usage will drive demand and should eventually lead to improved standardization and robustness of devices. In addition, developments such as optogenetics and the combination of modalities will lead to the development of devices that are less and less invasive.

The ethics of neurotechnology

The ethics associated with the use of this technology are important to consider when determining how to approach future avenues of research. Among ethical questions worth exploring are the following:

  • Questions associated with the “self” or “soul,” such as what makes a person who they are: If they are the sum of their parts, but some of those parts are artificial, what does this mean?
  • Questions around the potential for altered personality, particularly with interventions used to treat mental disorders: How much of a change is therapeutic, and how much of a change results in a fundamental alteration of someone’s being?
  • Questions of identity, which lie along the same lines: If the ways in which a person thinks or reasons are changed, does this change who they are?
  • Questions surrounding informed consent, which becomes an issue when performing procedures on psychologically compromised patients: If these same people are fundamentally altered by these interventions, can they still consent?


None of these questions are easy to answer and require ongoing discussions between stakeholders, including patients and users, in order to reach consensus as the technology advances.

Reimagining the partnership between brain and body

Closed-loop neurotechnology, while still in its infancy, holds significant promise for human health and wellness, among other applications. Consumer need drives these advancements and significant research efforts make them possible. By reimagining the partnership between brain and body, it is possible to develop effective interventions for neurological and psychological disorders that historically were poorly treated with pharmaceutical or other interventions.

To learn more about closed-loop neurotechnologies, read the IEEE Brain Initiative white paper “Future Neural Therapeutics.”

Read “Future of Neural Therapeutics: Technology Roadmap White Paper


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