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Background: Low-intensity Focused Ultrasound (FUS) is a new non-invasive method to focally modulate cortical function in humans. Previous studies have shown that FUS stimulation suppress cortex excitability of the primary motor cortex (M1) and other cortical areas. However, it remains unclear how FUS modulation influences the contralateral hemisphere. Interhemispheric inhibition (IHI) refers to the neurophysiological mechanism in which one hemisphere inhibits the opposite hemisphere. IHI may suppress undesired activities of the opposite hemisphere and has a physiological role in the coordination of bimanual movement. In the current study, we investigated how FUS modulation on M1 influences the short latency interhemispheric inhibition (SIHI) and long latency interhemispheric inhibition (LIHI).

Methods: We studied 5 healthy subjects. A test stimulus (TS) from a 60 mm TMS coil at intensity to produce∼ …