Fig. 1. The experimental setup of ultrasound stimulation and intracranial electrophysiological recording.

a Collimator guiding focused ultrasound to hair-removed scalp of an anesthetized rat model with an incidence angle of 40°, and a 32-channel electrode array inserted at an incidence angle of 40° into the left primary somatosensory cortex (S1) prepared through a craniotomy. The rat head and brain model were 3D reconstructed from T₂-weighted (T2W) MRI images⁹⁴. b The temporal profile of the transcranial focused ultrasound (tFUS). One-hundred cycles of sinusoidal wave formed a single ultrasound pulse, which generated a tone-burst at an ultrasound fundamental frequency (f₀) of 500 kHz for a tone-burst duration (TBD) of 200 μs. Such ultrasound pulses were repeated at certain PRF for a corresponding number within the ultrasound duration (UD) of 67 ms. The inter-sonication interval (ISoI) was 2.5 s, and some ISoI had 10% jittering, in which the ISoI was randomly selected from a uniform distribution centered at 2.5 s, bounded by ±250 ms. c The spatial coordinates of electrophysiological recordings. The coronal brain slice shows the location of electrode insertion with the insertion depth of 1 mm at the left S1. ML denotes the medial lateral distance from midline; AP denotes the anterior posterior distance from Bregma. d A sagittal view of the micro-CT image captured the surgical burr hole (approximate diameter: 2 mm) on the top of cranium. The micro-CT scan was repeated for six times independently with similar results. e The experimental setup of the sham ultrasound condition as a negative control (SFLP). The acoustic aperture of the ultrasound transducer was flipped by 180°, while the pulsed ultrasound and the intracranial recordings were maintained. f The experimental setup of another sham ultrasound condition as a control for bone-conduction (SSKF). The ultrasound incidence took place at an anterior location of the skull with active ultrasound transmission. g Another sham control on electrode shank, i.e., SSHK, is delivered to investigate potential effects of electrode vibrations on neuronal activation. As shown, in the SSHK sham condition, ultrasound is delivered to the shank of the electrode away from the recording sites as further depicted in Fig. 5d.