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. 2015 Dec 8;112(49):15202-7.
doi: 10.1073/pnas.1509265112. Epub 2015 Oct 26.

Behavioral assessment of sensitivity to intracortical microstimulation of primate somatosensory cortex

Sungshin Kim  1 , Thierri Callier  1 , Gregg A Tabot  2 , Robert A Gaunt  3 , Francesco V Tenore  4 , Sliman J Bensmaia  5
Affiliations

Behavioral assessment of sensitivity to intracortical microstimulation of primate somatosensory cortex

Sungshin Kim et al. Proc Natl Acad Sci U S A. .

Abstract

Intracortical microstimulation (ICMS) is a powerful tool to investigate the functional role of neural circuits and may provide a means to restore sensation for patients for whom peripheral stimulation is not an option. In a series of psychophysical experiments with nonhuman primates, we investigate how stimulation parameters affect behavioral sensitivity to ICMS. Specifically, we deliver ICMS to primary somatosensory cortex through chronically implanted electrode arrays across a wide range of stimulation regimes. First, we investigate how the detectability of ICMS depends on stimulation parameters, including pulse width, frequency, amplitude, and pulse train duration. Then, we characterize the degree to which ICMS pulse trains that differ in amplitude lead to discriminable percepts across the range of perceptible and safe amplitudes. We also investigate how discriminability of pulse amplitude is modulated by other stimulation parameters-namely, frequency and duration. Perceptual judgments obtained across these various conditions will inform the design of stimulation regimes for neuroscience and neuroengineering applications.

Keywords: brain–machine interfaces; just noticeable difference; neuroprosthetics; psychophysics; threshold.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Experimental design. (A) Experimental setup. (Inset) Temporal profile of ICMS pulse trains. (B) Trial structure in the two-alternative forced-choice tasks. The red-dotted circle denotes the animal’s point of gaze. (C) Chronically implanted electrode arrays for one of the two monkeys: one UEA was implanted in area 1 (green) and two FMAs were implanted in area 3b (yellow). (D) The UEA and the anterolateral FMA impinged on the hand representation in S1 (the other FMA impinged on the proximal limb representation and therefore was not used in the behavioral experiments).
Fig. 2.
Fig. 2.
Dependence of detectability on stimulation parameters. (A) Pulse width (28,126 trials from 13 electrodes). (B) Pulse train frequency (47,497 trials from 12 electrodes). (C) Pulse train duration (13,337 trials from four electrodes). (D) Pulse train duration and frequency (21,198 trials from 12 electrodes). ICMS amplitude was 40 μA.
Fig. 3.
Fig. 3.
(A) Threshold charge per phase from the pulse width manipulation. (B) Threshold number of pulses from the duration and frequency manipulation. (C) Threshold charge per phase from the pulse width and frequency manipulation.
Fig. 4.
Fig. 4.
Dependence of discriminability on stimulation parameters. (A) JND as a function of standard amplitude (20,052 trials from 16 electrodes). ICMS is at 300 Hz. (B) JND as a function of pulse train frequency, with a 70-μA standard (15,295 trials from nine electrodes). (C) JND as a function of pulse train duration, with a 70-μA standard (17,307 trials from nine electrodes).
Fig. S1.
Fig. S1.
Effects of polarity on the detection threshold in the (A) pulse width and (B) frequency manipulations.
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