Transcranial magnetic resonance imaging-guided high-intensity focused ultrasound 
(MRgHIFU) is gaining attention as a potent substitute for surgical intervention 
in the treatment of neurologic disorders. To discern the neurophysiologic 
correlates of its therapeutic effects, we applied MRgHIFU to an intractable 
neurologic disorder, essential tremor, while measuring magnetoencephalogram mu 
rhythms from the motor cortex. Focused ultrasound sonication destroyed tissues 
by focusing a high-energy beam on the ventralis intermedius nucleus of the 
thalamus. The post-treatment effectiveness was also evaluated using the clinical 
rating scale for tremors. Thalamic MRgHIFU had substantial therapeutic effects 
on patients, based on MRgHIFU-mediated improvements in movement control and 
significant changes in brain mu rhythms. Ultrasonic thalamotomy may reduce 
hyper-excitable activity in the motor cortex, resulting in normalized behavioral 
activity after sonication treatment. Thus, non-invasive and spatially accurate 
MRgHIFU technology can serve as a potent therapeutic tool with broad clinical 
applications.