Summary: Using minimally invasive brain implants, researchers evoked the sense of touch in patients who had lost tactile sensations. The technique could be used to restore tactile sensations to those with paralysis and neuropathy.
Source: Feinstein Institute for Medical Research
In a first-in-human study, researchers at The Feinstein Institutes for Medical Research elicited the sense of touch through a minimally-invasive electrode brain implant.
This research, published recently in Brain Stimulation, has the potential to help millions of people who live with paralysis and neuropathy.
Many illnesses and injuries, including stroke, diabetes or spinal cord injury, can produce loss of touch, which makes everyday movements difficult and takes an emotional toll on patients. Imagine not being able to feel a hot cup or the hand holding yours.
Previously, through brain-computer interface (BCI) technology, researchers have been able to electrically stimulate certain (gyral) areas of the brain and restore some sensation to the hand.
Through this new research, scientists have successfully shown that stimulation of harder to reach (sulcal) areas of the brain using stereoelectroencephalography (SEEG) electrodes can evoke precise sensory percepts in the fingertips.
“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 the study’s co-principal investigator, Chad Bouton, professor in the Institute of Bioelectronic Medicine at the Feinstein Institutes. “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.”
Through a minimally invasive procedure led by neurosurgeon, associate professor in the Institute of Bioelectronic Medicine at the Feinstein Institutes and co-principal investigator on the study, Ashesh Mehta, MD, two patients were implanted with the SEEG electrodes in the sulci (grooves) of the brain.
While providing electrical stimulation the study participants reported feelings of “tingling” or “sensation of electricity” localized to the hand and fingertips.
Restoring function with bioelectronic medicine
The Feinstein Institutes is the global scientific home of bioelectronic medicine, a field of research that combines molecular medicine, neuroscience and biomedical engineering to develop innovative therapies with the aim to treat diseases and conditions through targeted stimulation of nerves, including paralysis, arthritis, pulmonary hypertension and inflammatory bowel disease.
“Advances in artificial intelligence, brain electrodes and bioelectronic medicine hold significant promise for patients after spinal cord injury or stroke,” said Kevin J. Tracey, MD, president and CEO of the Feinstein Institutes.
“This remarkable study indicates bioelectronic medicine and neurosurgery could restore functions previously lost in these conditions.”
To research the brain’s response, the same electrodes used for stimulation were also used to record neural signals during mechanical stimulation of the hand. This process has allowed researchers to deepen the current knowledge of neural circuitry involved in processing touch-related sensations in the human brain, noted Santosh Chandrasekaran, Ph.D., investigator in the study and co-lead author on the paper with colleague Stephan Bickel, MD, Ph.D., also an investigator in the published study.
Recent biolectronic medicine progress at the Feinstein Institutes includes a published study around the most effective dose and time of day to stimulate the vagus nerve, a major nerve in the body that controls the body’s immune response.
Evoking highly focal percepts in the fingertips through targeted stimulation of sulcal regions of the brain for sensory restoration
•S1 sulcal stimulation via stereoelectroencephalography (SEEG) localized evoked percepts to fingertips more often than gyral stimulation.
•fMRI, myelin, and cortical thickness maps from Human Connectome Project delineated hand and finger representation in sulcal S1.
•S1 sulcal stimulation evoked percepts more focal than by cortical surface stimulation at the postcentral gyrus.
•Neural activity recorded in sulcal areas strongly correlated to mechanical tactile stimulation.
Paralysis and neuropathy, affecting millions of people worldwide, can be accompanied by significant loss of somatosensation. With tactile sensation being central to achieving dexterous movement, brain-computer interface (BCI) researchers have used intracortical and cortical surface electrical stimulation to restore somatotopically-relevant sensation to the hand. However, these approaches are restricted to stimulating the gyral areas of the brain. Since representation of distal regions of the hand extends into the sulcal regions of human primary somatosensory cortex (S1), it has been challenging to evoke sensory percepts localized to the fingertips.
Targeted stimulation of sulcal regions of S1, using stereoelectroencephalography (SEEG) depth electrodes, can evoke focal sensory percepts in the fingertips.
Two participants with intractable epilepsy received cortical stimulation both at the gyri via high-density electrocorticography (HD-ECoG) grids and in the sulci via SEEG depth electrode leads. We characterized the evoked sensory percepts localized to the hand.
We show that highly focal percepts can be evoked in the fingertips of the hand through sulcal stimulation. fMRI, myelin content, and cortical thickness maps from the Human Connectome Project elucidated specific cortical areas and sub-regions within S1 that evoked these focal percepts. Within-participant comparisons showed that percepts evoked by sulcal stimulation via SEEG electrodes were significantly more focal (80% less area; p = 0.02) and localized to the fingertips more often, than by gyral stimulation via HD-ECoG electrodes. Finally, sulcal locations with consistent modulation of high-frequency neural activity during mechanical tactile stimulation of the fingertips showed the same somatotopic correspondence as cortical stimulation.
Our findings indicate minimally invasive sulcal stimulation via SEEG electrodes could be a clinically viable approach to restoring sensation.