A minimally invasive implant that fits into the brain's grooves is capable of generating sensory stimulation in precise areas of the hand. Previously, scientists had succeeded in eliciting more generalized sensations throughout the hand, yet this more advanced technique marks a step forward in the quest to restore motor function in paralyzed individuals.
“From buttoning our shirts to holding a loved one’s hand, our sense of touch may be taken for granted until we lose it,” said study author Chad Bouton from the Feinstein Institutes for Medical Research. “These results show the ability to generate that sensation, even after it is lost, which may lead us to a clinical option in the future.”
Tactile sensations can be evoked in certain body parts by electrically stimulating specific regions of the brain’s primary somatosensory cortex. The difficulty, however, lies in the fact that the brain is a wrinkly old thing, with undulating ridges and grooves. Until now, researchers had only been able to access the raised ridges – or gyri – using high-density electrocorticography (HD-ECoG) electrodes, despite the fact that specific areas of the fingers are controlled by neurons that lie within the grooves, known as sulci.
In the journal Brain Stimulation, a team of researchers describes how they were able to place stereoelectroencephalography (SEEG) electrodes within the sulci of two patients. They succeeded in evoking a sense of touch within highly focused regions of the hand, including the fingertips.
The researchers first analyzed data from the Human Connectome Project, which includes cortical maps showing which areas of the somatosensory cortex correspond to which parts of the body. This enabled them to locate the regions that control tactile responses in the fingertips, helping them determine exactly where to place their SEEG electrodes.
The implants were then inserted into these specific sulcal regions within the brains of two epilepsy patients who had agreed to take part in the experiment while undergoing surgical treatment for seizures. When the electrodes were activated, both participants reported tingling sensations in their fingertips, with the affected area being considerably smaller and more precise than those normally stimulated by HD-ECoG electrodes.
The technique for implanting SEEG electrodes is also considerably safer and less invasive than more traditional methods, according to the study authors.
“The minimally invasive approach for their implantation reduces the risk of hemorrhage and infection to 1% and 0.8% respectively from that of 4% and 2.3% for subdural electrodes such as ECoG grids,” they explain.
While this research still has some way to go and the implant has not yet been tested in patients with paralysis, the authors are optimistic that “sulcal stimulation via SEEG electrodes could be a clinically viable approach to restoring sensation” in cases where this has been lost.