You might consider touch to be the least important of your five senses, but you would be wrong. Touch is central to your ability to orient yourself in space and move skillfully. The loss of touch also takes an emotional toll.

A new study in the journal Brain Stimulation offers evidence that minimally invasive stimulation of the deep grooves (sulci) on the outer layer of the brain could be a clinically viable option to re-spark the sense of touch in millions of people worldwide with paralysis, spinal cord injury, diabetes mellitus, or neuropathic pain who have lost the ability to feel touch.

Chad Bouton, PhD, professor at the Institute of Bioelectronic Medicine at the Feinstein Institutes, is co-principal investigator of the study.

The study conducted by researchers at the Feinstein Institutes for Medical Research, the scientific arm of Northwell Health, is reported in the article, “Evoking highly focal percepts in the fingertips through targeted stimulation of sulcal regions of the brain for sensory restoration.”

“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 Chad Bouton, PhD, professor at the Institute of Bioelectronic Medicine at the Feinstein Institutes and co-principal investigator of the study. “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.”

Santosh Chandrasekaran, PhD, and Stephan Bickel, MD, PhD, are co-lead authors on the paper.

“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.”

In earlier studies, brain-computer interface researchers have used intracortical and cortical surface electrical stimulation to restore sensations of touch and orientation to the hand. However, instead of stimulating the deeper more difficult-to-reach grooves or sulci on the undulating surface of the brain, earlier attempts have been restricted to stimulating the ridges (gyri).

The primary somatosensory cortex (in red) is associated with localization of touch, temperature, vibration, and pain. [Source: WikiCommons]
Since regions farther from the midline of the body, such as fingertips, are represented in regions of the primary somatosensory cortex that extend deep into the grooves, stimulating the ridges have not been very successful in evoking touch at the fingertips and other distal regions of the body.

To reach the deep grooves of the primary somatosensory cortex the researchers in this study used stereoelectroencephalography (SEEG) depth electrodes. These electrodes that are used to electrically stimulate the grooves of the primary somatosensory cortex also record neural signals and can be used to investigate the brain’s response to electrical and mechanical stimulation. 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, PhD, co-lead author on the paper with colleague Stephan Bickel, MD, PhD.

Ashesh Mehta, MD, neurosurgeon, associate professor in the Institute of Bioelectronic Medicine at the Feinstein Institutes, is co-principal investigator on the study.

Led by Ashesh Mehta, MD, neurosurgeon, associate professor in the Institute of Bioelectronic Medicine at the Feinstein Institutes, and co-principal investigator on the study, the authors stimulated the cerebral cortices of two patients with intractable epilepsy both on the ridges, via high-density electrocorticography (HD-ECoG) grids and in the grooves via SEEG depth electrodes to see which worked better in evoking precise sensations of touch in the hand.

Their results showed highly focused perception of touch can be evoked at the fingertips through SEEG stimulation deep in the grooves of the primary somatosensory cortex. The participants reported feelings of “tingling” or “sensation of electricity” localized to the hand and fingertips when electrically stimulated via SEEG.

Using neuroimaging tools designed by the Human Connectome Project, the authors showed the precise cortical subregions of the primary somatosensory cortex that evoke focused sensations of touch.

Comparing the two participants, the authors showed touch induced by SEEG electrodes was significantly more focal and localized to the fingertips more often, than by stimulation of ridges through HD-ECoG electrodes.