Learning-related patterns of CA1 spike trains parallel stimulation parameters optimal for inducing hippocampal long-term potentiation.

Recent studies have revealed 3 stimulation parameters that together comprise the temporal pattern of neuronal activation optimal for the induction of hippocampal LTP: high-frequency bursts, activity 100-200 ms prior to a burst, and burst delivery in phase with the ongoing hippocampal theta rhythm. The present paper reports that these 3 aspects of patterned neural activity, collectively referred to as "theta-bursting," are characteristic of the spike trains of CA1 pyramidal cells in rats during the sampling and analysis of learning cues in an odor discrimination task and during performances of a spatial memory task. In contrast, theta-bursting occurs relatively infrequently during behavioral events less directly related to task-relevant mnemonic processing. These findings suggest that the optimal conditions for the induction of LTP occur naturally in behaving animals, time-locked to behavioral events critical to learning.