Low-intensity transcranial ultrasound stimulation promotes the extinction of fear memory through the BDNF-TrkB signaling pathway

Synaptic plasticity plays a crucial role in the extinction of fearful memories. Low-intensity transcranial ultrasound stimulation (TUS) can modulate synaptic plasticity and promote the extinction of fear memories. However, the mechanism by which TUS promotes the extinction of fear memory remains unclear. This study aimed to explore whether and how synaptic plasticity under TUS is involved in modulating fear memory and the role of the brain-derived neurotrophic factor (BDNF)-the tropomyosin-related kinase B (TrkB) signaling pathway in this process. We used behavioral tests and two-photon fluorescence imaging to investigate the modulatory effects of TUS on fear memory and examined the formation/elimination of dendritic spines and the calcium activity of pyramidal neurons in the prefrontal cortex in mice in vivo. We found that TUS of the prefrontal cortex can promote fear memory extinction in mice while promoting dendritic spine formation, reducing dendritic spine elimination, increasing pyramidal neuron activity, and enhancing the expression of BDNF and its receptor TrkB. Conversely, inhibiting the BDNF-TrkB signaling pathway weakened these effects of ultrasound stimulation. Our study demonstrated that TUS could promote the extinction of fear memories, indicating that TUS has the potential to be used in the clinical treatment of patients with fear memory.