Transcranial focused ultrasound neuromodulation of the human primary motor cortex
Wynn Legon, Priya Bansal, Roman Tyshynsky, Leo Ai, Jerel K. Mueller
Scientific Reports 2018, 8 · 10.1038/s41598-018-28320-1
Abstract
Transcranial focused ultrasound is an emerging form of non-invasive neuromodulation that uses acoustic energy to affect neuronal excitability. The effect of ultrasound on human motor cortical excitability and behavior is currently unknown. We apply ultrasound to the primary motor cortex in humans using a novel simultaneous transcranial ultrasound and magnetic stimulation paradigm that allows for concurrent and concentric ultrasound stimulation with transcranial magnetic stimulation (TMS). This allows for non-invasive inspection of the effect of ultrasound on motor neuronal excitability using the motor evoked potential (MEP). We test the effect of ultrasound on single pulse MEP recruitment curves and paired pulse protocols including short interval intracortical inhibition (SICI) and intracortical facilitation (ICF). In addition, we test the effect of ultrasound to motor cortex on a stimulus response reaction time task. Results show ultrasound inhibits the amplitude of single-pulse MEPs and attenuates intracortical facilitation but does not affect intracortical inhibition. Ultrasound also reduces reaction time on a simple stimulus response task. This is the first report of the effect of ultrasound on human motor cortical excitability and motor behavior and confirms previous results in the somatosensory cortex that ultrasound results in effective neuronal inhibition that confers a performance advantage.
Abstract via europepmc.
Exposures
Exposure 1: Primary motor cortex (M1): hand-knob/FDI hotspot (single- and paired-pulse MEP experiments) and APB hotspot (reaction time experiment)
Target: primary motor cortex — “primary motor cortex (M1) hand-knob representation; FDI hotspot for the MEP experiments and APB hotspot for the reaction time experiment”
Device: custom-built
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | 0.36 | ✓✓✓⚑ |
| Pulse repetition frequency (Hz) | 1,000 | ✓✓✓ |
| Duty cycle (%) | not reportedpulse duration × PRF gives 36% | |
| Sonication duration (s) | 0.5 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 17.12 | ✓✓✓ |
| Free-field Ispta (W/cm²) | 6.16 | ✓✓✓ |
| In-situ estimate | simulationsingle value | |
| In-situ pressure (kPa) | 120 | ✓✓✓⚑ |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported |
Channel 1 was set to deliver tFUS at a pulse repetition frequency (PRF) of 1 kHz and channel 2 was set to drive the transducer at 500 kHz in burst mode using channel 1 as the trigger; channel 2 delivered 180 cycles per pulse and channel 1 delivered 500 pulses, resulting in a 500 msec duration waveform. For the single- and paired-pulse experiments, ultrasound was time-locked to occur 100 msec prior to the TMS pulse; for the reaction time experiment, ultrasound was time-locked to occur 100 msec prior to the visual stimulus. The sham condition involved turning over the transducer so no ultrasound was delivered while maintaining contact and equitable auditory artifact.
Flags from extraction
exposures[0].timing.pulse_duration_ms— Pulse duration was not stated directly in ms; it was converted from the stated '180 cycles per pulse' at the stated 500 kHz drive frequency (180/500000 Hz = 0.36 ms), the schema's sanctioned cycles-per-pulse-to-duration unit conversion.exposures[0].in_situ.pressure_kpa— Value ('~120 kPa') is an approximate figure from the Discussion referring to the modeled intracranial pressure, not a table/methods value with full precision.randomised— Experiments 1 and 2 describe conditions as 'counterbalanced across participants' while Experiment 3 explicitly states order was 'randomized across participants'; recorded as true for the whole study but the terminology differs by sub-experiment.auditory_control— Paper describes provision of ear protection to mask any audible transducer buzzing rather than a listed auditory-control vocabulary mechanism; recorded as 'other'.