Low intensity transcranial ultrasound stimulation (TUS) is an emerging method of brain neural regulation that can reversibly, non invasively, high-resolution, and highly penetrative regulate the electrophysiological activity of nerve cells without increasing tissue temperature. It has gradually been applied in neuroscience research and brain disease treatment. However, it is still unclear whether TUS can regulate the excitatory balance between the bilateral cerebral hemispheres.

In February 2023, Professor Sun Junfeng's team from the School of Biomedical Engineering at Shanghai Jiao Tong University and Professor Liu Dengtang's team from the Mental Health Center affiliated with Shanghai Jiao Tong University School of Medicine jointly published their latest research results in the Journal of Neural Engineering (IF=5.04). The article explained that excitatory TUS stimulation of the left motor cortex (M1) can induce long-term potentiation (LTP) effects, and can induce plasticity changes in long-term inhibition (LTP) of the contralateral motor cortex, indicating that TUS technology can regulate the excitability balance between the cerebral hemispheres. This validates the hypothesis of interhemispheric interaction inhibition.

The study adopted a randomized double-blind pseudo stimulus control design and used rTUS excitatory mode to intervene in the left motor cortex (M1) of 20 healthy subjects, once for 15 minutes. And the motor evoked potentials (MEPs) of bilateral M1 in the subjects were measured 15 minutes before rTUS intervention, 0 minutes before intervention, 0 minutes after intervention, 15 minutes after intervention, and 30 minutes after intervention; Use the Chinese Simplified Neurocognitive Test (C-BCT) to assess the cognitive function of participants before and after intervention. Cortical excitability is quantified by MEP, and long-term changes in MEP amplitude can serve as a reliable indicator of cortical plasticity.

▲ Research design drawings and rTUS parameters.

The study found that the ipsilateral MEP amplitude in the true stimulation group (n=20) significantly increased compared to baseline, and this effect persisted until 30 minutes after TUS intervention; Meanwhile, the amplitude of contralateral MEP significantly decreased compared to baseline, and this effect persisted until 15 minutes after intervention. RTUS induced an increase in laterality between bilateral MEPs. In the C-BCT cognitive test, the symbol encoding test showed significant changes before and after intervention. At the same time, the Composite scaled score of the C-BCT test showed a significant improvement after the intervention. The changes in the total score of C-BCT test are correlated with the amplitude changes and laterality index changes induced by rTUS in MEP. However, there was no significant change in MEP and C-BCT scores in the sham stimulation group (n=20). TUS stimulation induces intra hemispheric facilitation and inter hemispheric inhibition, and the effect can last for more than 30 minutes. The pseudo stimulus group did not exhibit this phenomenon.

▲ Changes in amplitude of bilateral MEP before and after TUS intervention in two groups.

This study confirms that rTUS intervention in excitatory mode can continuously increase M1 excitability on the stimulated side of the human brain, resulting in plasticity changes similar to long-term potentiation (LTP like); RTUS can regulate the excitability balance between the motor cortex hemispheres of the human brain and improve cognitive function to a certain extent. The above results indicate that rTUS has good potential in clinical intervention of brain diseases.