Experimental evaluation of an integrated focused ultrasound and electroencephalography approach for developing activation-informed neuroimaging
Ye Yuan, Jun You Li, Yongzhi Zhang, Sonia E. Vader, Tongsheng Zhang, Gösta Ehnholm, Jue Wang, Nathan McDannold, Yoshio Okada
NeuroImage 2026, 330, 121861 · 10.1016/j.neuroimage.2026.121861
Abstract
We experimentally evaluated the possibility of using an integrated focused ultrasound (FUS) - electroencephalography (EEG) approach to develop activation-informed neuroimaging for human functional brain mapping, enhancing the power of conventional approaches based solely on recording methods. A brief beam of FUS (50 μs, 4.0 MHz) with a focal transverse profile diameter of 0.4 mm determined in water was applied to the barrel cortex of rat in vivo on the dura, skull and scalp and evoked activity was recorded with EEG. We found using a laminar depth profile analysis and specific channel blockers that the stimulation within a safe pressure range could directly evoke a presynaptic spike (∼1 ms) in layer IV, followed by postsynaptic spikes (2.5-7 ms) in layer V and an excitatory wave (8-12 ms), both regulated by fast inhibition, and a major robust excitatory wave (20-30 ms) regulated by slow inhibition. Stimulus artifact was <1 ms, much shorter than for transcranial magnetic stimulation. All components were reliably detected from the scalp, skull, and dura using the 4 MHz and 2.2 MHz transducers. Thus, the FUS-EEG approach is capable of activating neurons transcranially and noninvasively recording a rich spectrum of excitatory and inhibitory activity starting immediately after stimulation. These characteristics can advance neuroimaging since this approach can identify normal electrophysiology and pathophysiology in known locations anywhere in the brain with precise timing and could possibly enhance the conventional approaches by validating and improving their spatial and temporal accuracy of localization.
Abstract via europepmc.
Exposures
Exposure 1: 4 MHz FUS to barrel cortex (dura/skull/scalp)
Target: primary somatosensory cortex — “barrel column receiving projection from whisker C2 (barrel cortex)”
Device: custom-built
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 4,000 | ✓✓✓ |
| Pulse duration (ms) | not applicable | |
| Pulse repetition frequency (Hz) | not applicable | |
| Duty cycle (%) | 0.00313 | ✓✓✓ |
| Sonication duration (s) | 0.000005, 0.001swept | ✓?⚑ |
| Free-field pressure (kPa) | 3,970 | ✓✓✓ |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | 0.0146 | ✓✓✓ |
| In-situ estimate | deratingsingle value | |
| In-situ pressure (kPa) | 3,840 | ✓✓✓ |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported |
Most experiments used a single continuous 4 MHz tone burst of 50 microseconds duration delivered via the exposed dura (or transcranially through skull/scalp), repeated across ~100-200 epochs (roughly every 1.6-2 s) for signal averaging; in one experiment burst duration was varied from 5 to 1000 microseconds to test temporal precision. In a separate paired-burst paradigm, trains of four 50-microsecond bursts were presented with inter-burst intervals of 10-500 ms to probe fast and slow cortical inhibition. Derated peak negative pressure up to 3.84 MPa (MI=1.9) was used.
Exposure 2: 2.2 MHz (also called 2.1 MHz) FUS to barrel cortex (dura/skull/scalp)
Target: primary somatosensory cortex — “barrel column receiving projection from whisker C2 (barrel cortex)”
Device: custom-built
| Waveform | continuous | |
|---|---|---|
| Fundamental frequency (kHz) | 2,200 | ✓✓✓⚑ |
| Pulse duration (ms) | not applicable | |
| Pulse repetition frequency (Hz) | not applicable | |
| Duty cycle (%) | not reported | |
| Sonication duration (s) | not reported |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| 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 | |
| Pressure, domain unspecified (kPa) | 1,200 | ✓✓✓⚑ |
| Ispta, domain unspecified (W/cm²) | 0.0013 | ✓✓✓ |
The in-house conical 2.2 MHz transducer (same as used previously in vitro) was applied to the same barrel-cortex target via dura, skull or scalp using a pressure of 1.2 MPa (MI=0.81); focal FWHM was 1.1 mm transverse by 5.0 mm longitudinal.
Flags from extraction
exposures[0].unspecified_domain.pressure_kpa— PNP labelled 'underated' (likely 'unrated', i.e. not derated) but the accompanying Ispta calculation uses brain density/speed of sound rather than water; domain (free-field vs in-brain) is ambiguous so value placed in unspecified_domain.exposures[0].timing.sonication_duration_s— Primary experiments used a fixed 50 microsecond burst (see protocol_description); only the explicitly stated tested range (5-1000 microseconds) from a separate duration-effect experiment is recorded as the list here.exposures[1].fundamental_frequency_khz— Paper alternately calls this transducer '2.2 MHz' (used in most passages) and '2.1 MHz' (e.g. 'We repeated this study using the 2.1 MHz transducer...'); likely the same device but the frequency label is inconsistent within the text.exposures[1].unspecified_domain.pressure_kpa— Not stated whether the 1.2 MPa value is a free-field (water-tank calibrated) or in-brain pressure; placed in unspecified_domain.exposures[0].timing.waveform— set to pulsed by the tie-break: the ruled timing has a pulse repetition or duty cycle