The most complex electrical device we possess isn’t in our pockets, it’s in our heads. Ever since Emil du Bois-Reymond’s discovery of electrical pulses in the brain and Santiago Ramón y Cajal’s realisation that the brain was composed of separate pieces, called neurons, we have known that the brain’s behaviour stems from its independent electrical parts. Many scientists are studying electronic implants that can affect how our brains think and learn. New research on conducting polymers that work well in the body may bring us one step closer to the ability to manually overhaul our own brains.
The immediate brain health implications of plugging electronics into the brain, even with a very basic level of control, would be astounding. The connections in the brain can adapt in response to their environment, forming the basis of learning. This ‘plasticity’ means the brain could adapt in response to implanted electronics, for example by connecting to prosthetic limbs and learning to control them. Implantable electrodes which can excite or inhibit neural signals could also be used for treatments of disorders stemming from bad neural patterns, such as epilepsy and Parkinson’s disease.Since the 1970s, brain-computer interfaces have been studied intensively. Passive electrodes which can record brain waves are already in widespread medical use. Invasive but accurate mapping of brain activity can be done by cutting the skull open, as neurosurgeons do during surgery to avoid tampering with important areas. Less invasive methods like electroencephalography (EEG) are helpful but more sensitive to noise and unable to distinguish different brain regions, not to mention individual neurons. More active interfaces have been built for artificial retinas and cochleas, though the challenge of connecting to the brain consistently and for a long time makes them a very different thing from our natural eyes and ears. But what if we could directly change the way the brain works, with direct electronic stimulation?
However, current neural electrodes made from metal cause problems when left in the brain long term. The body views foreign bodies in the brain as a problem and over time protective cells work to minimize their impact. This immune response not only damages the brain region around the electrode, it actually works to encapsulate the electrode, insulating it electrically from the brain and removing its purpose in being there.
These issues arise because of how hard and unyielding metal is compared to tissue, as well as the defense mechanisms in the body against impurities in metal. Hypoallergenic metals are used to combat this issue in piercings and jewelry, but the brain is yet more sensitive than the skin to invasive metals. A new approach being researched by scientists is the use of conducting polymers to either coat metal electrodes or to even comprise them, removing metal from the picture altogether.
Conducting polymers are plastics, which are more soft and mechanically similar to living tissue than metal. Additionally, they conduct ions (as do neurons in the brain) and are excellent at transducing these to electronic signals, giving high sensitivity to neural activity. Researchers at the École des Mines de Saint-Étienne in France have now demonstrated flexible, implantable electrodes which can be used to directly sense of stimulate brain activity in live rats, without the immune reaction plaguing metal electrodes.
It’s a big step from putting organic electronics in the brain and reading out activity to uploading ourselves to the cloud. But while scientists work on improving resolution in space and time in order to fully map a brain, there is already new hope for those suffering from neurodegenerative diseases, thanks to the plasticity of the brain and the conductivity of plastic.