Invasive brain-computer interfaces (BCIs) allow for direct communication between the brain and external devices, offering immense potential for restoring lost functions and even enhancing brain capabilities.
Recent advances are bringing this emerging technology closer to widespread clinical use.
Invasive BCIs involve surgically implanted electrodes to record from or stimulate the brain.
This allows for much higher resolution interfaces than noninvasive methods like EEG.
There are two main types:
- Intracortical microstimulation (ICMS) electrodes implanted in the cortex
- Deep brain stimulation (DBS) electrodes implanted in deeper brain structures
Key facts:
- Invasive BCIs can decode neural signals to control robotic limbs, computer cursors, and speech synthesizers
- ICMS can restore tactile sensation and crude vision by stimulating the somatosensory and visual cortex
- DBS is FDA approved to treat movement disorders like Parkinson’s and psychiatric conditions like depression
- Closed-loop systems allow real-time bidirectional communication between the brain and computers
- Materials advances and surgical robotics are improving electrode biocompatibility and minimizing tissue damage
- Ethical guidelines are needed to prevent misuse as these technologies become more powerful
Source: Brain Sci. 2023
Decoding Neural Signals for Device Control
Invasive BCIs can decode patterns of electrical activity in the brain to control prosthetic limbs, computer cursors, and other external devices.
This requires accurately translating the language of the brain.
Recording from motor areas like the primary motor cortex allows researchers to predict intended movements from neural firing patterns.
Algorithms like Bayesian decoders, Kalman filters, and artificial neural networks can translate these signals in real time to control robotic arms, computer cursors, and speech synthesizers.
Recent advances allow unprecedented control over assistive devices:
- Paralyzed patients used invasive BCIs to control computer cursors and robotic limbs capable of reaching, grasping, and drinking coffee.
- Using signals from the speech motor cortex, an artificial voice synthesizer could imitate sentences a patient was silently thinking.
- Neural decoders allowed a paralyzed patient to type at 90 characters per minute just by thinking about writing.
As materials and machine learning algorithms improve, invasive BCI device control is becoming faster, more natural, and more accurate.
This offers hope for severely paralyzed patients to regain functioning and independence.
Restoring Touch and Sight Through Intracortical Microstimulation
Intracortical microstimulation (ICMS) involves implanting electrode arrays into the cortex to stimulate patterns of neural activity.
This can crudely restore tactile and even visual sensations.
Restoring Touch
The primary somatosensory cortex receives sensory input from the skin and body.
ICMS in this region can produce percepts of pressure, vibration, and skin contact.
Patients stimulated here report distinct sensations like touches and taps on specific fingers and hands.
This artificial sense of touch can provide critical feedback for controlling prosthetic limbs.
ICMS restores the sensation of objects grasped in a robotic hand, allowing more fluid and natural control.
Without this closed-loop tactile feedback, patients struggle to properly modulate grip strength and manipulate objects.
As materials improve to increase the longevity of implanted electrodes, ICMS sensory feedback could become a standard feature of neural prostheses.
Vision Restoration: Sight for the Blind
Similar to tactile feedback, stimulating the visual cortex can produce spots of light and color known as phosphenes.
Though crude, ICMS-evoked phosphenes could convey visual information like shapes and letters to blind patients. Recent advances include:
- A blind patient was able to identify stimulation-induced phosphenes forming letters and object outlines.
- Monkeys could recognize letters and shapes encoded by simultaneously stimulating hundreds of electrodes implanted in their visual cortex.
Though far from natural vision, ICMS prosthetics offer hope for those with incurable blindness to regain some functional sight.
Deep Brain Stimulation for Treating Brain Disorders
Deep brain stimulation (DBS) involves implanting electrodes in deeper structures beneath the cortex.
It is an FDA approved therapy for treating Parkinson’s, essential tremor, dystonia, and obsessive compulsive disorder.
High frequency electrical stimulation of subcortical targets like the thalamus, subthalamic nucleus, and globus pallidus can suppress the tremors, involuntary movements, and obsessive behaviors associated with these disorders.
The mechanisms likely involve disruption of pathological neural firing patterns.
DBS can reduce Parkinson’s medication dosages by 30-50% and significantly improve quality of life for many patients.
It is also being explored for treating epilepsy, depression, addiction, PTSD, and other psychiatric conditions.
However, finding optimal stimulation targets and parameters requires a more complete understanding of the underlying neural circuits involved in these disorders.
Advances in neuroimaging, biomonitoring, and neuroinformatics will help refine DBS therapy.
Closed-Loop BCIs and Bidirectional Communication
Early invasive BCI systems primarily focused on one-way communication: decoding motor signals to control devices.
However, new closed-loop systems allow for real-time bidirectional interactions between the brain and computers.
This could involve using decoded neural activity to control robotic limbs or speech synthesizers, while also using ICMS to provide tactile or visual feedback from the devices.
Researchers have termed these systems brain-machine-brain interfaces (BMBIs).
Closed-loop operation will also improve DBS by modulating stimulation based on real-time monitoring of neural biomarkers for symptoms of a disorder.
A recent study demonstrated closed-loop DBS effectively treating severe depression by continually optimizing stimulation parameters.
Fully bidirectional BCIs will enable seamless integration of the brain with computers and machine learning algorithms.
This could restore lost functions or even enhance cognitive capabilities.
Improving Biocompatibility to Increase Safety & Longevity
A major challenge for clinical implementation of invasive BCIs is improving electrode biocompatibility to increase safety and longevity.
Current silicon electrode arrays often fail within months to a few years due to tissue reactions.
New electrode materials like flexible polymer composites can minimize inflammation and scarring.
Novel implantation methods also reduce tissue damage, like inserting electrode threads through blood vessels instead of drilling through the skull.
Surgical robotics allow precise, minimally-invasive electrode placement while avoiding blood vessels.
Automated implantation will also make these surgeries safer and more accessible.
With better electrodes and surgical techniques, invasive BCI systems may remain viable and effective for many years.
This will increase adoption for clinical therapies.
The Future of Brain Augmentation & Ethics
Invasive BCIs currently aim to restore lost functions like movement, touch, and sight.
However, the technology could eventually do much more.
Bidirectional brain-computer integration may enhance cognitive capabilities and mental health beyond normal levels.
As materials and implantation methods improve, healthy individuals may opt for neural implants as a form of brain augmentation.
But these technologies come with risks like brain hacking, privacy breaches, and unintended mental and physical side effects.
Unethical use could fulfill dystopian fears of government thought control.
Guidelines are urgently needed for responsibly advancing invasive BCIs.
While the potential is immense, we must ensure these technologies are developed for human betterment rather than manipulation and control.
Their implementation should be subject to ethical principles of transparency, security, accountability, and respect for personal rights.
Brain-Computer Interface Tech: The Future
Invasive brain-computer interface technology is progressing rapidly from lab research toward clinical therapies.
While there are still challenges to overcome, bidirectional BCI systems could soon restore lost functions, treat mental health conditions, and enhance natural brain capabilities.
But anticipating and wisely navigating the immense implications of directly hacking the brain will determine if this technology uplifts humanity or leads to catastrophe.
References
- Study: Modulating brain activity with invasive brain-computer interfaces
- Authors: Zhi-Ping Zhao et al. (2023)
