High frequency tone bursts of ultrasound are capable of increasing the sensitivity of rat motor cortex to electrical stimulation. In this study, 11.75 MHz ultrasound pre-stimuli were delivered to the forelimb motor region of the rat cortex followed by an electrical pulse train to assess changes in cortical activation. The temporal peak intensity of the ultrasound delivered to the brain ranged from 100 to 150 W/cm(2). Tone bursts of 10 to 50 ms in duration were delivered once per second over periods of 30 to 240 seconds. The intracortical microstimulation (ICMS) current needed for forepaw motor response decreased by as much as 40% when applying 50 ms ultrasound pulses. Brain excitability changes were seen with a thermal index (TI) as low as 2.0. Ultrasound application alone was not able to induce motor responses.