I am looking for references that discuss the scaling of biochemical signals in dendritic spines with spine size/synaptic strength. A recent paper (Walker et al. 2017) reports attenuation of NMDA receptor Ca2+ signal with increasing spine size, consistent with a scenario where increase in synaptic efficacy (AMPAR/NMDAR conductance) is overcompensated by spine volume expansion. However, it is not clear to me if this trend is also reflected in the activation of downstream biochemical signals like calmodulin (CaM) or CaM-dependent enzymes. This relates to the issue of how the threshold for plasticity might be regulated as a function of synapse strength/spine size. Would be very interested in knowing if this kind of data has been reported in the literature.