Introduction – Recording human brain activity can be crucial for monitoring normal and aberrant brain function. Functional ultrasound imaging (fUSI) is an emerging technique that offers sensitive, large-scale (50mm x 38mm), high-resolution (200 μm) imaging of neurovascular function. However, fUSI cannot be performed through the adult human skull due to signal attenuation. Several cranioplasty materials, such as polymethyl methacrylate (PMMA), are acoustically transparent and may allow fUSI to monitor neural activity following a cranioplasty. In this study, we aimed to demonstrate that fUSI can image neurovascular activity and decode task information in humans through a sonolucent cranioplasty.

Methods – We collected data across more than a year from one participant who received a PMMA cranioplasty following a traumatic brain injury. We used fUSI to measure neurovascular activity through the PMMA cranioplasty as our participant performed different tasks, including playing guitar. We used this fUSI data to build a general linear model of the brain regions involved in each task and to train linear classifiers that could decode our participant’s intended actions. To understand which cortical regions best discriminated the different task actions, we performed a searchlight analysis with a 600 μm radius.

Results – We successfully demonstrated fUSI can image human neurovascular activity through a sonolucent cranioplasty. Our linear model robustly identified cortical regions modulated by different tasks (p<1e-10, t-test,). Using our linear classifier, we successfully decoded task information with 84.7% accuracy (p<1e-15, 1-sided binomial test). Our searchlight analysis identified several cortical regions important for decoding the task information and these results closely matched the linear model.

Conclusion – This study demonstrates that fUSI provides unprecedented access to brain activity in adult humans with sonolucent cranioplasties. This access has the potential to directly benefit brain injury patients and open new doors to neuroscience discoveries and the development of improved treatments.