IL1B and infection: This time point was chosen for several reasons: (1) both the young and aged animals have recovered from the overt symptoms of illness (e.g., fever, loss of appetite, etc.; Barrientos et al., 2006); (2) levels of hippocampal IL-1β are still significantly elevated in the aged rats but have returned to near pre-infection levels in the young rats (Barrientos et al., 2009); and (3) the aged rats show significant deficits in hippocampus-dependent long-term memory, but the young rats do not (Barrientos et al., 2006).