Mind-Controlled Bionic Limbs

Thought Controlled Bionic Limb

Mind-controlled bionic limbs are now a reality thanks to numerous scientific breakthroughs. Dual-site myoelectric sensors placed against the skin’s surface offer the simplest method of delivering a limited degree of mind control. Pattern Recognition and/or targeted nerve reinnervation can significantly extend these capabilities. And bidirectional neural interfaces offer the promise of sensory feedback in combination with mind control.

Built-in Myoelectric Sensors

Bionic arms for below-the-elbow amputations tend to use dual-site myoelectric sensors to detect muscle movements through the skin in the residual forearm. These signals are then translated into actions by the bionic hand.

Myoelectric Prosthesis

For example, if the wearer clenches the remaining muscles in the forearm, the bionic hand will close.

Most below-the-elbow bionic limbs use this method of mind control because it doesn’t require surgery. The sensors can be installed and calibrated at the time of delivery.

The drawback to this method is its limited degree of control. It cannot be used to control individual fingers, as one major limitation.

Below-the-elbow bionic arms compensate for this by allowing users to manually change hand positions and grip configurations. Clenching and extending the forearm muscles then has a different effect for each position. This short video demonstrates the combined actions required to eat with a fork:

Pattern Recognition

This intriguing technology involves a combination of more myoelectric sensors (8 in some models) with artificial intelligence (AI). The idea is that each intended hand movement generates, in  the residual limb, its own unique pattern of myoelectric signals that can be used to tell the bionic arm/hand how to move.

The following video provides a good example of the increased mind control available using this type of approach:

Targeted Muscle Reinnervation (TMR)

Even after amputation, the mind retains a neural map of the missing limb. It can still feel the limb and even experience pain from it. This is where the term “phantom limb” originates.

If an amputee attempts to move a phantom limb, the brain still sends nerve signals to the amputated muscles. They’re just not there to respond.

Targeted Muscle Reinnervation (TMR) surgically reassigns nerves from amputated muscles to residual muscles.

As explained in the previous sections, myoelectric devices depend on the electrical signals generated by muscle movement. By rewiring nerves to activate other muscles, TMR  helps generate the electrical signals needed for more sophisticated control of a bionic limb.

Targeted Muscle Reinnervation Can Play Key Role in Mind-Controlled Bionic Limbs

A controller then maps these additional signals to movements such as bending the elbow or changing hand positions. Combinations of electrical signals can form patterns that allow for even finer control, such as moving individual fingers.

This video shows a TMR recipient using his bionic hand to play piano:

Bidirectional Neural Interfaces

Bidirectional Neural Interfaces go a step beyond TMR. By implanting sophisticated sensor arrays into a residual limb, scientists can tap into the mind’s neural map of the missing portion of the limb. Not only can they use this information to improve mind control over a bionic hand. If they add sensors to the hand, they can send sensory information back to the brain by stimulating the appropriate nerves. For more information on this subject, see our article on Bionic Touch.

The proper term for this approach is “biomimetic”, which means using synthetic methods to mimic biochemical processes.

One of the big advantages of taking a biomimetic approach with bionic limbs is that it makes moving them much more natural. The amputee simply moves his or her phantom limb, and the technology translates this into actual movements in the bionic equivalent.

But there’s more. There is a symbiotic relationship between what we feel with our natural limbs and how we move them. As we move, we feel, and as we feel, we adjust how we move. By restoring this relationship, we allow amputees to exert far more dexterous and intuitive control over their bionic prostheses, as you can see in this video:

Another advantage of this approach is that it seems to relieve the pain associated with phantom limbs. This is a big issue for many amputees.

Mind Control for Bionic Legs & Feet

More attention has been paid to mind-controlled bionic arms & hands than for lower limbs.

Part of the reason is because a lot of progress has been made with intelligent bionic legs that use local microprocessors to automatically adjust to tasks, as shown in this video:

Another reason is that, until recently, lower limb amputations didn’t typically preserve the muscle movements required for mind control.

A new technique, called the “Ewing amputation”, recreates these movements. This makes mind control more feasible, as shown in this video:

Which technique will win out? Because mind-controlled bionic limbs tend to make amputees feel more whole again, we think this will ultimately be the solution of choice. But we wouldn’t be surprised to see a combination of mind control and localized microprocessor adjustments – perhaps the best of both worlds.

Related Information

For more information on upper limb bionics, see Understanding Bionic Arms & Hands.

For more information on lower limb bionics, see Understanding Bionic Legs & Feet.