Livewired Brain #5: Output Control

In earlier blogs, we’ve seen sensory substitution and sensory addition. But, as David Eagleman writes in Livewired:

“That’s only the input half of the story.”

Let’s next look into the output-related reorganization of the brain.

 

When a limb is paralyzed, the motor system parts of the brain reorganize:

“The motor areas optimize themselves to drive the available machinery.”

In fact, brains are not “predefined for particular bodies”. Instead, brains “adapt themselves to move, interact, and succeed”:

“(Watch a human baby and notice how she is) learning how her motor output corresponds to the sensory feedback she receives.”

It doesn’t stop with babies, of course. We continue the “same learning method to attach extensions to our bodies”. That’s how we learn to ride a bicycle. Or a skateboard. Or to surf the waves:

“The specifics of the devices’ weight, joints, movements and controllers – everything you can do with them – work their way into your brain circuitry.”

Leading to the Terminator analogy:

“It’s like the Terminator after Sarah Connor has burned it and crushed its legs: it keeps going, operating with a different body plan but pursuing its goal nonetheless.”

 

Scientists have created devices that can take brain signals in paralyzed folks through a “different route”, i.e., instead of going via neurons to muscles (which don’t work) to instead control an artificial limb. Leading Eagleman to muse:

“If you have the brain, you can build a new body, but not the other way around.”

In some paralyzed patients, scientists have even “eavesdropped on the motor system” of the brain via electrodes, run machine learning algorithms to interpret the activity, and thereby “bypass the damaged spinal cord and jump instead to the muscle simulator”. Voila! The (paralyzed) arm can now move based on the brain’s command. They’ve even used those tapped brain signals to move a cursor on the computer screen. No matter how alien it may seem, the brain learns to control any appendages you add to the body! Of course:

“The brain learns to drive its body best when there’s a closed loop of feedback: not just output, but input as well that verifies the interaction with the world.”

 

In the age of virtual reality, Eagleman says more and more of us will experience the ability to control things and appendages that aren’t part of our biological body. For fun, or for deadly serious stuff like deactivating a bomb via the virtual reality controlled robot. Sadly, as of now, “avatar robotics” is too expensive.

 

Eagleman signs off on the topic by wondering whether a new appendage that the brain learns to control would gradually change the experience of the world. Not just a little, but enough for the brain itself to change:

“Who we are depends on how the whole brain is wired. Tweak the body and you may tweak the person.”