A few weeks ago I covered a story about a prosthetic arm that promised to eventually restore the sensation of touch to patients who had lost limbs, and now this week another study has been released with similar goals but a very different method. The study, published yesterday through the PNAS, bridged the damaged connection between two functional parts of the brain in rats to restore both reaching and grasping. A neural implant was used to reconnect the rodent equivalent of the primary motor cortex, which is found in the frontal lobe and controls movement, with its somatosensory cortex, which is in the parietal lobe and is responsible for processing the various signals that make up the sensation of touch.
In the past, it was believed that damage to the motor cortex affected the signals being sent directly to the spinal cord, and this in turn impaired reaching and grasping. But the motor cortex also communicates with the somatosensory cortex, where it gets information about where limbs are located in space. This study was examining if perhaps it was the loss of this connection that was responsible for hampering movement, rather than damage to the spinal pathways. By reconnecting the somatosensory cortex to the motor cortex through the rat’s premotor cortex, researchers were able to restore those lines of communication and in doing so repair the rat’s reaching and grasping abilities.
The neural implant itself is a remarkable piece of equipment. It uses a closed-loop circuit design to circumvent the damaged pathways in the motor cortex. Researchers designed a battery-powered microdevice capable of registering and recording individual action potentials, and then sending an electrical current to another, separate group of neurons in response.
Effectively, they created a sort of external pathway for nerve signals that would not normally have been communicated, transmitting them straight from the somatosensory cortex to the premotor cortex through their device. It is called a closed-loop system because the signals move from the brain into the device and then back into the brain, as opposed to simply having the target neurons constantly stimulated by an implant. The authors believe that these results may be translatable to the human brain and that their work could help patients who have suffered brain damage from sources such as serious trauma or a stroke.
As the paper points out, this study highlights one of the growing trends in neuroscience. The model of the brain being comprised of separate regions with each controlling separate functions is quickly being abandoned in favor of a more interconnected structure, where motor skills and cognitive abilities are spread across lobes and cortices to form much more complex webs of neural activity. Here we see how, as opposed to the motor cortex being the only part of the brain involved in movements such as reaching and grasping, it is reliant on input from the region of the brain that tracks the body’s movement through space, a region found in an adjacent lobe. While this certainly does create a more complicated and convoluted picture of the brain, it also means that treatments such as this, where these complexities can be utilized to repair serious damage and restore function, may become more and more common.