A Robust Encoding Scheme for Delivering Artificial Sensory Information via Direct Brain Stimulation

Abstract

Innovations for creating somatosensation via direct electrical stimulation of the brain will be required for the next generation of bi-directional cortical neuroprostheses. The current lack of tactile perception and proprioceptive input likely imposes a fundamental limit on speed and accuracy of brain-controlled prostheses or re-animated limbs. This study addresses the unique challenge of identifying a robust, high bandwidth sensory encoding scheme in a high-dimensional parameter space. Previous studies demonstrated single dimensional encoding schemes delivering low bandwidth sensory information, but no comparison has been performed across parameters, nor with update rates suitable for real-time operation of a neuroprosthesis. Here, we report the first comprehensive measurement of the resolution of key stimulation parameters such as pulse amplitude, pulse width, frequency, train interval and number of pulses. Surprisingly, modulation of stimulation frequency was largely undetectable. While we initially expected high frequency content to be an ideal candidate for passing high throughput sensory signals to the brain, we found only modulation of very low frequencies were detectable. Instead, the charge-per-phase of each pulse yields the highest resolution sensory signal, and is the key parameter modulating perceived intensity. The stimulation encoding patterns were designed for high-bandwidth information transfer that will be required for bi-directional brain interfaces. Our discovery of the stimulation features which best encode perceived intensity have significant implications for design of any neural interface seeking to convey information directly to the brain via electrical stimulation.

Generating artificial sensations with spinal cord stimulation in primates and rodents

“…Our results on behavioral sensitivity to detection of sensation in rodents and primates were comparable to those observed with Intracortical Microstimulation (ICMS) of S1 (5,17). Notably, sensitivity to stimulus amplitude increased with increasing pulse width, frequency, and duration of stimulation.…”

“…Frequency modulation has been historically considered a promising method for providing sensory feedback with several studies showing that animals are capable of discriminating ICMS frequencies and that frequency modulation obeys Weber's law. (4,(20)(21)(22), While ICMS amplitude modulation in monkeys failed to follow Weber's law (5), experiments in rats showed that modulation of perceived intensity by amplitude and pulse-width modulation followed Weber's law (17). In our study, we investigated whether rats and monkeys could learn to discriminate SCS frequencies.…”

Multi-channel intra-cortical micro-stimulation yields quick reaction times and evokes natural somatosensations in a human participant

“…Intra-cortical micro-stimulation (ICMS) patterns were generated using four key parameters [59]: pulse amplitude, pulse-width, stimulation frequency and total stimulation duration (Figure 1C). Pulse-amplitude ranged from 1-100µA, pulse-width from 44-400µsec, while the stimulation frequency was fixed at 300Hz and duration lasted up to 1s.…”

“…Previous studies have suggested electrical charge as a powerful modulator of somatosensory sensations in single-channel ICMS [28], [59], [60]. Specific spatial patterns of charge, delivered over multiple ICMS channels, may be an important parameter for targeting specific percepts or somatotopic locations [34] [39].…”

W:Ti Flexible Transversal Electrode Array for Peripheral Nerve Stimulation: A Feasibility Study

“…tingling, as reported by the users [2]- [4], [6]- [11]. However, different groups approach this problem from different angles with marked differences in the site in the nervous system where the stimulation is delivered: central [12]- [14] vs. peripheral nervous system [2], [15]- [17]; invasive [2], [7], [8], [10], [18] vs. non-invasive [5], [17], [19]; and the way the neural stimulation is modulated to convey sensory precepts: biomimetic [8]- [10], [20]- [23] vs. abstract [13], [17], [21], [24]. We believe that this diversity is due to three main reasons: 1. uncertainty on how to best sense and convert sensory information from the environment to electrical patterns to stimulate the nervous system and evoke naturalistic sensation; 2. lack of technologies for targeted delivery of this information to the nervous system; and 3. research still ongoing on the development of biocompatible neural interfaces that allow direct communication with the peripheral nervous system without causing physical damage and pain.…”