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Posted: Oct 21, 2010
The electronics for smart brain implants
(Nanowerk News) Imagine that, one day, we would be able to implant electronics in the brain. Electronics that restore damaged regions of the brain. Or impaired functions, such as speech, hearing, vision, movement control, or even memory.
Sounds like science-fiction?
From an electronics point of view, we are fast zooming in on biological structures. The size of the electronic circuits that we can make is already equal to the size of human circuits, i.e. nerve and brain cells. And electronic and biological circuits both talk through the same mechanism: electrical signals.
Of course, there is a lot that we don't yet fully understand. We still have to figure out the language of the brain cells. What does a cell say when it fires a signal to its neighbors? How are memories fixed in the brain? How are they read out? And we still have no definitive map of the brain, the connectome of the human brain.
Still, there are already electronics that talk to brains. With deep brain stimulation (DBS) probes, it is possible to relieve the situation of people with severe Parkinson's, depressions, or obsessions. DBS techniques are well established and have already been used successfully to improve the lives of thousands of patients.
But DBS doesn't take advantage of all the possibilities of today's electronic technology. The electrodes are large (mm-scale), and stimulate thousands of brain cells at once, insensitive to where the real culprits of the patient's disease are. Also, the DBS electronics cannot measure if the applied stimulus is overshooting or undershooting. So DBS is a fairly crude technology, with many unwanted side effects.
Scheme of a module-level processed heterojunction cell with inter-digitated back contacts.
At imec, we're working on improving DBS technology. We've created electrodes that are much smaller (down to 10µm) and that can stimulate small groups of nerve cells. And we've worked on the electronics to make the stimulus a directed beam, pointing towards the targeted cells, instead of stimulating the whole region around the probe. Last, we're also working on a closed-loop stimulation, where signals from brain cells are measured and used to steer the applied stimuli.
In maybe 5 years, these techniques will lead to DBS probes in clinical use that are much smarter and more widely applicable than today's crude appliances.
But when I look further out, say 10 to 20 years from now, I believe the technology that we are developing today will eventually be used in smart brain implants. Such implants could replace and repair damaged brain tissue. Or fill brain cavities caused by tumors, accidents, or brain infarcts.
With the help of imaging and 3D prototyping technology, it will be possible to create highly precise 3D implants, such as are already used today to replace damaged bone tissue. We would of course have to make these implants in flexible, stretchable, biocompatible materials, so that they fit in comfortable with the surrounding brain tissue. On the surface of these implants, there will be thousands of micro-electrodes that can individually stimulate and listen to the neurons in their neighborhood.
What will such implants be able to do?
First, they will passively fill a cavity with a biocompatible, quasi-living, signaling body. What we see now is that neurons surrounding a cavity will stop functioning because they no longer feel any activity. An implant will prevent the cavity from being filled with scar tissue and fluid. And it will indicate to the surrounding brain cells that all is 'business as usual'.
But we will eventually also learn to use the implant as an active body. An active body, first, that stimulates the growth of neurons. We could make sponge-like implants, for example, that allow nerve cells to populate the implant. And second, a body that bridges signals, that reconnects the neural pathways that were destroyed. Of course, we don't know exactly which neurons were connected in the first place. But the brain is plastic and self-healing. We see with retinal implants, for example, that the brain is able to re-establish suitable connections if it is given the pathways to do so. So the implant will have to support this learning and healing phase, with the help of selective, directed closed-loop stimuli.
The science-fiction of today regularly proves to be the reality of tomorrow. Based on the R&D we do today, I believe that one day, 10-20 years from now, we will be able to implant electronics in the brain. Smart implants filled with electronics to restore damaged regions and functions of the brain.
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