What Jaime Lannister wishes he knew…
Being a huge game of thrones fan, I love finding GoT analogies wherever possible. So, when I recently came across a very cool scientific achievement, I couldn’t help thinking of a GoT reference, more specifically, Sir Jaime Lannister.
Spoiler alert: If you haven’t progressed beyond the first few seasons, this post might contain spoilers.
The scene: Jaime returns to King’s landing after trouble on the road left him alive, but minus one hand. Pompous as the Lannisters are, Cersei arranges for the perfect replacement: a golden hand. It is humorous (and pitiful) to watch him test out the useless block of gold; the most useful thing he can do with it is wave! So, a sense of touch or differentiating silk from steel with it is out of question.
This is not a big surprise, of course. The human brain perceives stimuli, such as touch, through special biological sensors spread out under the skin. Mechanical stimulation of these sensors via touch generates an electric potential, which travels to the brain through specialized cells called nerves. The frequency i.e., the rate of fired electric impulse by the brain cells is directly dependent on the applied pressure. Damaged nerves, such as those in amputated limbs, result in a loss of communication between the brain and skin-receptors, depriving the victims of the perception of touch.
Fast-forward (from whatever time-period GoT belongs to) to the year 2015. Researchers in the group of Zhenan Bao in Stanford University make a giant leap in prosthetics by developing an artificial skin that can ‘feel’. The skin-like sensor, called Digital Tactile system (DiTact), is a stretchable thin film with embedded electronic circuits that sense pressure. It follows a sequence of perception-conversion-stimulation.
Perception: The pressure sensor consists of billions of carbon nanotubes packed inside an elastic film. When pressure is applied, the nanotubes are compressed together, allowing them to conduct electricity that is measured in volts.
Conversion: The next component is an electric oscillator, which converts the DC voltage from the pressure sensor to a series of voltage spikes, at a frequency that is controlled by the amplitude of the input voltage. This means that the output frequency increases with increasing pressure stimulation, mimicking the mechanoreceptors in our skin.
Stimulation: The final element of the sensor was designed to prove the utility of the output signal in conversing with the brain cells. The frequency output from the oscillator was used to stimulate brain cells from mice. Optogenetic stimulation was used, which is a novel approach that combines optical and genetic engineering methods. A protein in the brain cells was genetically modified, such that it responded to light-induced stimulation by generating an electric impulse. The output frequency from DiTact was used to generate pulses of light from a LED source. The team observed that the resulting electronic signal from mice-neurons matched the frequency of illumination, which itself was correlated to the initial pressure stimulus.
In its current form, DiTact presents an artificial skin-like sensor that can be used in prosthetic limbs with silver nanowires conducting electrical signals to the brain to achieve a realistic sensation of touch. This non-invasive sensor brings the dream of prosthetic limbs with tactile functions one step closer. Future sensors could include other aspects of touch, such as the ability to distinguish between different textures and response to dynamic stimuli.
Now, wouldn’t Jaime procuring such a high-tech prosthetic hand make a great plot-twist?
Tee, B. C.-L. et al. Science 350, 313–316; 2015