Hippocampal granule cells transmit information about behaviourally-relevant stimuli to CA3 pyramidal cells via mossy fibre synapses. These synapses express a form of long-term potentiation (LTP) that is non-Hebbian and does not require NMDA receptors (Nicoll and Schmitz, 2005). Mossy fiber LTP is thought to be induced and expressed presynaptically, hence, the major determinant of whether LTP occurs is activity in the granule cells. However, it remains unclear whether mossy fiber LTP can be induced by activity patterns that granule cells exhibit in vivo, and — if so — what context generates these patterns. To address these issues, we examined granule cell activity from in vivo recordings of 68 granule cells performed previously during performance of a delayed nonmatch-to-sample (DNMS) task (Wiebe and Staubli, 1999, 2001) and found that granule cells exhibit a wide range of spike patterns. We next performed In vitro experiments using extracellular field potential recordings of mossy fibre synaptic transmission in 500μm thick transverse hippocampal slices. These experiments revealed that some, but not all, of the in vivo recorded granule cell spike patterns could induce LTP (3 out of 6 tested). By further defining the activity thresholds for mfLTP in hippocampal slices, we found that mfLTP can only be induced by spike patterns that fire in high frequency bursts (>10Hz) with a low average firing frequency (<0.33Hz). Using this information, we then screened for supra-threshold bursts of activity during the DNMS task. In a subset of cells, supra-threshold bursts occurred preferentially during the sampling phase of the task. If supra-threshold bursting took place later, during the delay phase, task performance was disrupted. We conclude that mfLTP can be induced by granule cell spike patterns during a memory task, and that the timing of mfLTP induction can predict task performance.