A double-blind replication attempt of offline 5Hz-rTUS-induced corticospinal excitability

Transcranial ultrasound stimulation (TUS) is a promising new form of non-invasive neuromodulation. As a nascent technique, replication of its effects on brain function is important. Of particular interest is offline 5 Hz repetitive TUS (5 Hz-rTUS), originally reported by Zeng et al. (2022) to elicit lasting corticospinal excitability increases, with large effect sizes. Here, we conducted a pre-registered (https://osf.io/p5n4q) replication of this protocol that benefited from three additional features: double-blind application of TUS, neuronavigation for consistent TMS positioning, and individualised 3D acoustic simulations to assess M1 target exposure to TUS. Changes in resting motor thresholds (rMT), motor-evoked potential (MEP) amplitude, short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) in response to TUS (5 Hz-rTUS vs. sham) were measured in the right first dorsal interosseous (FDI), abductor digiti minimi (ADM), and abductor pollicis brevis (APB) muscles. Transducer location was determined by the TMS-hotspot for motor representations of the right FDI, as in the original work. No significant effects of 5 Hz-TUS (vs. sham) were observed. Post-hoc simulations showed considerable variability of the acoustic focus, which was outside the anatomical M1-hand area in 67% of participants-in line with the known poor correspondence of TMS-hotspot location and M1-hand area. Our results indicate that the effect sizes of the neuromodulatory effects of 5 Hz-rTUS on M1 may be more variable than previously appreciated. We suggest that double-blinding, neuronavigated TMS, individualised acoustic simulations for TUS targeting and pre-registration will aid reproducibility across studies.