Estimation of the spatial profile of neuromodulation and the temporal latency in motor responses induced by focused ultrasound brain stimulation

Abstract

This study investigates the spatial profile and the temporal latency of the brain stimulation induced by the transcranial application of pulsed focused ultrasound (FUS). The site of neuromodulation was detected by using 2-deoxy-2-[18F]fluoro-D-glucose positron emission tomography (FDG-PET) immediately after FUS sonication on the unilateral thalamic area of the Spague-Dawley rats. The latency of the stimulation was estimated by measuring the time taken from the onset of the stimulation of the appropriate brain motor area to the corresponding tail motor response. The brain area showing elevated glucose uptake from the PET image was much smaller (56±10% in diameter, 24±6% in length) than the size of the acoustic focus, which is conventionally defined by the full-width at half-maximum (FWHM) of the acoustic intensity field. The spatial dimension of the FUS-mediated neuromodulatory area was more localized, approximated to be full-width at 90%-maximum of the acoustic intensity field. In addition, the time delay of motor responses elicited by the FUS sonication was 171±63 (s.d.) ms from the onset of sonication. When compared to latencies of other non-ultrasonic neurostimulation techniques, the longer time delay associated with FUS-mediated motor responses is suggestive of the non-electrical modes of neuromodulation, making it a distinctive brain stimulation method.

Suppression of EEG visual-evoked potentials in rats through neuromodulatory focused ultrasound

“…Hydrogel (Aquasonic, Parker Laboratories, Fairfield, NJ) was applied to the interface between the rat's scalp and the water bag. The position of the rat was adjusted relative to the FUS transducer by manipulating the three-axes platform (MF70, Proxxon, Hickory, NC, and Lab Jack, Edmund Scientifics, Tonawanda, NY) attached to the stage, and the acoustic focus was aimed at the visual cortex under the stereotactic guidance [11]. …”

“…The geometry of the neuromodulatory area at the acoustic focus, estimated at the full-width at 90%-maximum, was roughly an elongated ellipsoidal shape (3.7 mm in diameter, 5.6 mm in length). The detailed procedure to map the acoustic pressure field can be found elsewhere [11]. …”

“…Although most of the current studies have focused on examining the excitatory effects of FUS [11], some studies have reported neural suppression. For example, the suppression of the visual cortex activity by FUS was shown via the reduction of the signal amplitude of the visual evoked potentials (VEP) and blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signals in rabbits [5].…”

Electrophysiological Source Imaging of Brain Networks Perturbed by Low-Intensity Transcranial Focused Ultrasound

“…Recently, transcranial focused ultrasound (tFUS) has been pursued for non-invasive neuromodulation due to its high spatial resolution [10-12]. In vivo experiments (in animals) have been reported using a range of ultrasonic parameters achieving either activation or suppression of neural activity.…”

Evaluation of polyvinyl alcohol cryogel as an acoustic coupling medium for low‐intensity transcranial focused ultrasound

“…For example, most of the high‐intensity focused ultrasound (HIFU) utilizes a water bath, either surrounding (such as in a commercial transcranial FUS system; Martin et al, ) or situated over the transducer that aims at the anatomy‐of‐interest (such as in abdominal sonication; Pediconi et al, ). Recently, we have adopted a plastic bag containing degassed water to couple a single‐element FUS transducer to the skin surface in rodent experiments aimed at neuromodulation (Min et al, ; Yang et al, ; Yoo et al, ; Kim et al, ; Kim et al, ) or in human experiments aimed at eliciting tactile sensations (Lee et al, ). However, the bag containing the degassed water lacks mechanical support and tends to shift depending on the sonication beam path, especially when the sonication path is not aligned with the gravity, severely limiting the choice of location for the sonication target and orientation of the beam path.…”