Good question. Appears that they use contextual fear conditioning to assess memory.
From the research article:
"We chose to use the immediate-shock fear conditioning paradigm (Fanselow, 1990; Rudy et al., 2002) as the learning task. Here, foot shock is delivered very quickly upon exposure to the experimental context on the fear conditioning day. However, the rats are preexposed to the context at an earlier time. The preexposures are required so that the subjects are able to form a 'conjunctive representation' of the context, so that it can be associated with the shock on the conditioning day (Rudy et al., 2002). We chose this fear conditioning paradigm because it is highly and specifically dependent on the hippocampus (Rudy et al., 2002), and we have already shown that E. coli interferes with memory of this task in aging rats (Barrientos et al., 2006)"
From the research article: "We chose to use the immediate-shock fear conditioning paradigm (Fanselow, 1990; Rudy et al., 2002) as the learning task. Here, foot shock is delivered very quickly upon exposure to the experimental context on the fear conditioning day. However, the rats are preexposed to the context at an earlier time. The preexposures are required so that the subjects are able to form a 'conjunctive representation' of the context, so that it can be associated with the shock on the conditioning day (Rudy et al., 2002). We chose this fear conditioning paradigm because it is highly and specifically dependent on the hippocampus (Rudy et al., 2002), and we have already shown that E. coli interferes with memory of this task in aging rats (Barrientos et al., 2006)"