Third, we report that dendritic calcium firing leading to LTP can occur not only by activation of adjacent PF-EPSPs, but also by activity in the sparser AF tract, implying a less stringent spatial organization of synaptic inputs compared to the one necessary for mGluR1- and endocannabinoid-mediated PF-LTD [25]. Here, GRM1 is linked to atrial fibrillation.