Did you ever wonder if you could control an artificial arm? And that this artificial arm could also give feedback back to you about what you feel. For instance, a hot cup of coffee or an ice cube.
To realize such approaches in the future, the brain’s basic understanding and the methods and devices used in neuroscience need to advance. In the example mentioned here, it is essential to record neural activity and write back feedback on this activity. To control an artificial arm, you need to think that you control an arm, and the signal has to be recorded from the motor cortex. At the same time, to get feedback about the temperature of the touched object, the digital signal from the temperature sensors in the artificial arm needs to be transferred or written into your sensory cortex.
It is especially problematic in neuroscience to record neuronal signals with implanted devices for a long time with high signal quality. The brain’s movement, the electrochemical interactions of an implanted electrode with biological tissues, and the inflammation process are just a few of the causes that result in a slow degradation of the signal quality. But in patients, you need good signal quality for a very long time.
The second problem is to record brain activity while also delivering light simultaneously. Why would we need to shine light into the brain? Because a technique called -optogenetics – allows the opening of ion channels with the use of light (see figure 1).
Those ion channels are genetically introduced into the membrane of a neuron, and they are typically closed. However, the light of a specific wavelength opens those channels and allows positively charged ions to flow inside and therefore activates the neuron, which then fires with an action potential. Thus, the neuron is active now.
This process can also work the other way around. Inhibit neurons from firing and sending signals. Inhibiting works by activating ion channels that bring negatively charged ions inside the neuron and inhibit the neuron from firing.
While recording the activity from the brain and simultaneously stimulate it with light, there is one problem. The light disturbs the signal in common electrodes. Which makes it challenging to interpret the recorded signals.
We asked ourselves whether it is possible to develop an electrode that can be implanted chronically during long-term experiments and allows that light to pass through the electrodes without disturbing the signal.
Therefore, we as neuroscientists worked together with engineers to develop such an electrode (see figure 2). Such a process takes many years since electrodes have to be built and later tested. And they always have to be refined. We mainly worked on the long-term stability, transparency, and flexibility of the material. In the end, we successfully developed an electrode array that is first long-term stable and, secondly, allows to control neural activity via light delivery. It is in its design different from previous approaches. Because the materials used are a lot more long-term stable and, as an additional benefit, also easier to produce. In the end, the main advantage is that they are less complicated.
With this and similar research all over the world, we will in the further future be able to help disabled people how lost, for instance an arm. But there are limitations to this promise. In this specific example, it starts with the process of introducing these proteins into the neuronal membrane of humans and ends with how the light should be delivered in human subjects. All of this is possible in our animal models in the lab but not as easy for human subjects.
In science, one has to understand that everyone makes a small contribution, which will sum up later to achieve something more significant. As much as I would like to tell you that this research we conducted here might help patients very soon, as much you should know that this is not the whole truth. Many inter-disciplinary teams around the world, work together for decades to be able to reach the final aim. And one also has to consider that progress has to happen within the neuroscientific field, but in this case, advancements have to occur in the engineering science and material science, and in neurosurgery.
For science to progress faster is sometimes luck, but it also highly depends on money and the workforce. As we have seen during the pandemic, vaccines are researched and produced much faster if there is an urgent need and combined force worldwide. And if basic research would not have been performed for many decades, the baseline knowledge to allow that fast vaccine development would not be available.
However, bureaucratic hurdles and limited resources will lead to less progress. But in the end, science is at the tip of the iceberg a society has to take care of. Probably the major contributor to save the world or at least make it longer livable will be science. However, one can only afford to invest a lot into science if the political and societal structures are more stable and more urgent needs are fulfilled.
To summarize these last thoughts: With this research study here, we won’t be able to control an artificial limb with sensory feedback immediately. One has to see it as a small contribution, like many other similar small contributions in that field. Slowly we will move towards that final dream.
If I learned one thing as a scientist, then it is an extreme amount of patience and trust that the future will be brighter if we work hard.
Brosch et al. 2020 An optically transparent multi-electrode array for combined electrophysiology and optophysiology at the mesoscopic scale J. Neural. Eng 046014