Effective intracortical microstimulation parameters applied to primary motor cortex for evoking forelimb movements to stable spatial end points

Abstract

High-frequency, long-duration intracortical microstimulation (HFLD-ICMS) applied to motor cortex is recognized as a useful and informative method for corticomotor mapping by evoking natural-appearing movements of the limb to consistent stable end-point positions. An important feature of these movements is that stimulation of a specific site in motor cortex evokes movement to the same spatial end point regardless of the starting position of the limb. The goal of this study was to delineate effective stimulus parameters for evoking forelimb movements to stable spatial end points from HFLD-ICMS applied to primary motor cortex (M1) in awake monkeys. We investigated stimulation of M1 as combinations of frequency (30-400 Hz), amplitude (30-200 μA), and duration (0.5-2 s) while concurrently recording electromyographic (EMG) activity from 24 forelimb muscles and movement kinematics with a motion capture system. Our results suggest a range of parameters (80-140 Hz, 80-140 μA, and 1,000-ms train duration) that are effective and safe for evoking forelimb translocation with subsequent stabilization at a spatial end point. The mean time for stimulation to elicit successful movement of the forelimb to a stable spatial end point was 475.8 ± 170.9 ms. Median successful frequency and amplitude were 110 Hz and 110 μA, respectively. Attenuated parameters resulted in inconsistent, truncated, or undetectable movements, while intensified parameters yielded no change to movement end points and increased potential for large-scale physiological spread and adverse focal motor effects. Establishing cortical stimulation parameters yielding consistent forelimb movements to stable spatial end points forms the basis for a systematic and comprehensive mapping of M1 in terms of evoked movements and associated muscle synergies. Additionally, the results increase our understanding of how the central nervous system may encode movement.

Restoring Behavior via Inverse Neurocontroller in a Lesioned Cortical Spiking Model Driving a Virtual Arm

“…Recent years have seen extraordinary progress in technologies that not only allow us to read the brain signals, but also to artificially stimulate neural circuits. Neurostimulation will be the best way to demonstrate our understanding of neural codes (Stanley, 2013 ), by injecting signals that produce specific natural sensory sensations (O'Doherty et al, 2011 ; Choi et al, 2012 ; Klaes et al, 2014 ), motor behaviors (Overduin et al, 2012 ; Van Acker et al, 2013 ), or memory (Hampson et al, 2013 ) and cognitive (Hampson et al, 2012 ) influences. Clinically, a major challenge for the next generation of motor-function-restoring brain-machine interfaces (BMIs) is the incorporation of realistic somatosensory feedback via cortical stimulation (Bensmaia and Miller, 2014 ).…”

“…These factors limit the ability to predict the outcome of neurostimulation and, therefore, to achieve targeted neural control. Consequently, neurostimulation studies have been predominantly confined to measuring the elicited neural responses (Clark et al, 2011 ; Van Acker et al, 2013 ).…”

Muscle synergies obtained from comprehensive mapping of the primary motor cortex forelimb representation using high-frequency, long-duration ICMS

“…Pairs of multistranded stainless steel wires (Cooner Wire) were inserted into each muscle to a length of~2-3 cm with~5 mm separation between the ends of the wires. Placement accuracy was tested by observing muscle twitches induced from short stimulus trains (Grass SD9 Stimulator, West Warwick, RI), and cross talk was tested before recording (Hudson et al 2010;Park et al 2000;Van Acker et al 2013). All surgeries were performed as directed by the standards of the Guide for the Care and Use of Laboratory Animals, published by the United States Department of Health and Human Services and the National Institutes of Health.…”

“…EMG data were collected from 24 muscles of the forelimb using intramuscular electrodes with hardware set gains, filtered from 30 Hz to 1 kHz (Grass P511) and digitized at 4,000 Hz. Cross talk between EMG electrodes was examined by compiling and comparing EMG-triggered averages to poststimulus effects (Buys et al 1986;Van Acker et al 2013). Based on this analysis, first dorsal interosseus in monkey X was deleted from the database.…”

Cortical Action Representations

“…Kaas (2005, 2009) used electrical stimulation to extensively map the parietal cortex and motor cortex of monkeys and prosimians and found action categories in distinct cortical zones. Van Acker et al (2013) obtained complex movements of the limbs including hand-to-mouth movements on stimulation of the monkey motor cortex. Van Acker et al (2013) obtained complex movements of the limbs including hand-to-mouth movements on stimulation of the monkey motor cortex.…”