Cognitive deficits are among the most devastating changes associated with the aging process. Age-related decrement in performance on learning tasks is correlated with substantial changes in neuronal signal processing in the hippocampus. Here we show that elevated expression of small-conductance Ca2+-activated K+ channels (SK channels) of the SK3 type in hippocampi of aged mice contributes to reduced long-term potentiation (LTP) and impaired trace fear conditioning, a hippocampus-dependent learning task.