Pins and Needles - The Neural Basis of Touch

This week’s paper can be found here: The neural basis of perceived intensity in natural and artificial touch

We’ve all experienced numbness in a part of our bodies. Whether it was at the dentist’s office or after sitting on your foot for too long, there’s always that moment when you realize that you can’t tell where a particular part of your body is. Usually, this becomes apparent when you bite your cheek after a novocaine shot or trip on your foot upon getting up. This feeling highlights our sense of tactile stimulation, which alert us to different pressures of touch. We don’t normally bite the inside of our cheek, because we feel our teeth touching it and back off. Similarly, we don’t normally trip over our feet, because we can feel the ground beneath us when we put our foot down. Our abilities to interpret different levels of tactile stimulus help us to navigate the world around us. 

Unfortunately, not everyone has the ability to leverage this sense. Those who have lost their sensory nerves in a particular area, whether due to amputation or internal severance, live in a world where they are always tripping on their feet or biting their cheeks. This can result in further injuries (ex. touching a hot stove and not feeling the heat), and can lead to the need for further medical care, as many patients compensate for their lack of tactile sensation using abnormal gait or adjustments (ex. leg amputees may shift their weight to the opposite hip, causing cartilage damage and arthritis). 

However, this may not be the case for much longer. Researchers at Case Western Reserve University have been developing an implanted electrical interface that can electrically stimulate severed nerves. Recently, they used this technology to determine what types of electrical stimulation can be used to restore that sense of tactile stimulation in patients. Specifically, they looked at how the stimulation pulse width (how long a nerve is stimulated for at a time) and stimulation frequency can be tailored to represent different levels of perceived touch in patients with this electrical interface. 

Their discovery has immediate applications, as many scientists are developing prosthetics that are ready to incorporate such an implantable electric neural interface. In doing so, anyone with nerve damage may be able to regain normal limb function through the use of these “smart” prosthetics.