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Manipulation of cortical excitability can be experimentally achieved by the application of transcranial random noise stimulation (tRNS). TRNS is a novel method of non-invasive electrical brain stimulation whereby a random electrical oscillation spectrum is applied over the cortex. A previous study recently reported that application of weak 10-min tRNS over primary motor cortex (M1) enhances corticospinal excitability both during and after stimulation in the healthy human brain. Here, blood oxygenation level dependent (BOLD) MRI was used to monitor modulations in human sensorimotor activity after the application of 4-min tRNS. Activation maps for a right hand index–thumb finger opposition task were obtained for nine subjects after sham and 1-mA tRNS in separate sessions. TRNS of the left-hemispheric sensorimotor cortex resulted in a decrease in the mean number of activated pixels by 17%, in the hand …