Transcranial Focused Ultrasound Modulates Intrinsic and Evoked EEG Dynamics
Jerel Mueller, Wynn Legon, Alexander Opitz, Tomokazu F. Sato, William J. Tyler
Brain Stimulation 2014, 7, 900-908 · 10.1016/j.brs.2014.08.008
Abstract
Background The integration of EEG recordings and transcranial neuromodulation has provided a useful construct for noninvasively investigating the modification of human brain circuit activity. Recent evidence has demonstrated that focused ultrasound can be targeted through the human skull to affect the amplitude of somatosensory evoked potentials and its associated spectral content. Objective/hypothesis The present study tests whether focused ultrasound transmitted through the human skull and targeted to somatosensory cortex can affect the phase and phase rate of cortical oscillatory dynamics. Methods A computational model was developed to gain insight regarding the insertion behavior of ultrasound induced pressure waves in the human head. The instantaneous phase and phase rate of EEG recordings before, during, and after transmission of transcranial focused ultrasound (tFUS) to human somatosensory cortex were examined to explore its effects on phase dynamics. Results Computational modeling results show the skull effectively reinforces the focusing of tFUS due to curvature of material interfaces. Neurophysiological recordings show that tFUS alters the phase distribution of intrinsic brain activity for beta frequencies, but not gamma. This modulation was accompanied by a change in phase rate of both beta and gamma frequencies. Additionally, tFUS modulated phase distributions in the beta band of early sensory-evoked activity but did not affect late sensory-evoked activity, lending support to the spatial specificity of tFUS for neuromodulation. This spatial specificity was confirmed through an additional experiment where the ultrasound transducer was moved 1 cm laterally from the original cortical target. Conclusions Focused ultrasonic energy can alter EEG oscillatory dynamics through local mechanical perturbation of discrete cortical circuits.
Abstract via europepmc.
Exposures
Exposure 1: tFUS to somatosensory cortex (EEG site CP3)
Target: primary somatosensory cortex — “somatosensory cortex, targeted from 10-20 EEG site CP3 (effectively targeting S1)”
Device: Blatek · Blatek, Inc. ✓
| 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) | 800 | ✓✓✓ |
|---|---|---|
| Free-field Isppa (W/cm²) | 23.87 | ✓✓✓ |
| 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 |
A total of 120 ultrasonic stimuli (0.5 s each) were delivered at an ISI of 6 s (with 4 s positive randomisation) from EEG site CP3, with median nerve stimulation time-locked to occur 100 ms after tFUS onset (120 median nerve stimuli per condition). Sham and tFUS were run in a single session, counterbalanced across subjects; a separate cohort received tFUS 1 cm lateral to CP3 as a spatial-specificity control.
Flags from extraction
exposures[0].timing.pulse_duration_ms— Earlier in the same paragraph the methods state the pulse duration 'was set to 0.36 ms' (180 cycles at 0.5 MHz), but the summary waveform line states 'PD 360 ms'; 360 ms is inconsistent with the stated PRF (1 kHz) and stimulus duration (500 pulses in 0.5 s), so 0.36 ms is almost certainly correct and 360 ms a units typo. Recorded as stated in the summary specification line (360 ms) per the no-correction rule.n_subjects— Paper gives two separate cohort sizes (18 at CP3, 7 at the 1-cm-lateral site) and never states a combined total.