Differences between synaptic plasticity thresholds result in new timing rules for maximizing long-term potentiation

► New LTP timing rules are identified for adult hippocampus. ► A post-TBS refractory period for synaptic signaling and LTP induction is identified. ► There are synapses with high and low threshold for LTP induction in adult hippocampus. ► We propose spine crosstalk primes high threshold synapses for later potentiation. ► Ampakine treatment facilitates potentiation of high threshold synapses.