Experimental chronic periodontitis, caused when live P. gingivalis (ATCC33277) was given by oral gavage every 48 h over 6 weeks, has been shown to impair learning and memory and elicit neuroinflammation (i.e., increased expression of TNF-α, IL-1β and IL-6 in the brain) in middle-aged mice (12 months old), although not in young individuals (4 weeks old) [46]. Here, TNF is linked to chronic periodontitis.