Effects of transcranial focused ultrasound on human primary motor cortex using 7T fMRI: a pilot study
Leo Ai, Priya Bansal, Jerel K. Mueller, Wynn Legon
BMC Neuroscience 2018, 19 · 10.1186/s12868-018-0456-6
Abstract
Background Transcranial focused ultrasound (tFUS) is a new non-invasive neuromodulation technique that uses mechanical energy to modulate neuronal excitability with high spatial precision. tFUS has been shown to be capable of modulating EEG brain activity in humans that is spatially restricted, and here, we use 7T MRI to extend these findings. We test the effect of tFUS on 7T BOLD fMRI signals from individual finger representations in the human primary motor cortex (M1) and connected cortical motor regions. Participants (N = 5) performed a cued finger tapping task in a 7T MRI scanner with their thumb, index, and middle fingers to produce a BOLD signal for individual M1 finger representations during either tFUS or sham neuromodulation to the thumb representation. Results Results demonstrated a statistically significant increase in activation volume of the M1 thumb representation for the tFUS condition as compared to sham. No differences in percent BOLD changes were found. This effect was spatially confined as the index and middle finger M1 finger representations did not show similar significant changes in either percent change or activation volume. No effects were seen during tFUS to M1 in the supplementary motor area or the dorsal premotor cortex. Conclusions Single element tFUS can be paired with high field MRI that does not induce significant artifact. tFUS increases activation volumes of the targeted finger representation that is spatially restricted within M1 but does not extend to functionally connected motor regions. Trial registration ClinicalTrials.gov NCT03634631 08/14/18.
Abstract via europepmc.
Exposures
Exposure 1: tFUS to M1 thumb representation
Target: primary motor cortex — “M1 thumb representation (hand knob), targeted via fMRI-localised finger representation”
Device: custom-built
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | 0.36 | ✓✓✓⚑ |
| Pulse repetition frequency (Hz) | 1,000 | ✓✓✓ |
| Duty cycle (%) | 36pulse duration × PRF gives 36% | ✓✓✓ |
| Sonication duration (s) | 0.5 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 16.95 | ✓✓✓ |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not reported | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported |
Each tFUS stimulation delivered 180 cycles per pulse at 500 kHz (0.36 ms pulse duration) at a pulse repetition frequency of 1 kHz for 500 pulses, giving a 500 ms stimulus duration; this waveform was delivered every two TRs (2.75 s) for a total of 54 stimulations per scan, interleaved with a cued finger-tapping task.
Flags from extraction
exposures[0].timing.pulse_duration_ms— Pulse duration is derived from the stated 180 cycles per pulse and 500 kHz driving frequency (180/500000 s = 0.36 ms) via the cycles-per-pulse/frequency conversion the schema explicitly permits, and matches the '36% duty cycle' separately stated in the Discussion (0.36 ms / 1 ms period).exposures[0].device— Transducer is described only as 'custom made' with no manufacturer name; classified as custom_or_research.exposures[0].in_situ— The paper qualitatively states that skull attenuates free-field pressure by a factor of 6-7 (based on prior modelling) but does not report a specific derated in-situ intensity or pressure value for this cohort.randomised— The order of tFUS and sham conditions was counterbalanced across participants, which is a systematic (non-random) design; the paper does not use the word randomised, so this field is recorded as not_reported rather than inferred as true or false.