This study examined the effects of medial septal (MS) and mammillary b
ody (MB) radio-frequency lesions in an automated delayed-matching-to-s
ample (DMTS) procedure using lever-position stimuli and rats. Memory p
erformance pre- and postsurgery was assessed with a negative exponenti
al decay function fitted to bias-free measures of recognition. Part 1
showed that MS, but not MB or sham-control surgery, impaired DMTS perf
ormance. This impairment in the MS group was best characterized as an
increase in the rate of forgetting. Part 2 examined the interaction be
tween MS and MB lesion effects and proactive interference arising from
responses made on the previous DMTS trial. The results indicated that
proactive interference effects were similar for all groups. These res
ults provide further support for the critical role of the MS region in
memory function but indicate that damage to this brain region does no
t disrupt memory function through a heightened sensitivity to proactiv
e interference.