CREB1 and Parkinson disease: The results of this study demonstrated that oral administration of B. breve A1 restores the facilitation of contextual fear extinction in PD mice via the prevention of abnormal changes in hippocampal synaptic plasticity, the mechanism of which is probably due to the normalizing of an aberrant higher induction of neuropsin without stimulating the cAMP/cAMP response element-binding protein (CREB) pathway in the hippocampus.