TLR4 and Cognitive impairment: These results suggest that Paenalcaligenes hominis and Escherichia coli can cause hippocampal inflammation by inducing TLR4- and IL-1R-mediated NF-κB activation in innate immune cells such as microglia and successively suppress NF-κB-mediated BDNF expression in the hippocampus, resulting in cognitive impairment.