Young Investigators Colloquium 1

Most neurons in the mammalian brain receive thousands of excitatory synaptic inputs that are widely distributed along the dendritic arbor and activated with varying degrees of synchrony. Summation of unitary synaptic excitatory postsynaptic potentials (EPSPs) at the dendrite is crucial for initiation of the action potential. Patterned neuronal activity, which is known to modify synaptic transmission, has been shown to modulate dendritic structure and ion channel properties. However, whether and how neuronal activity can modify dendritic integrative function is largely unknown. In this study, we examined the efficacy of EPSP summation in hippocampal CA1 pyramidal neuron before and after the induction of long-term synaptic potentiation (LTP) induced by a paired theta burst stimulation (pTBS). We found that the linearity of both spatial summation (summation of synchronous EPSPs from two independent synaptic inputs) and temporal summation (consecutive EPSPs from the same input) of EPSPs increased following LTP induction, in an inputspecific manner. Such enhancement of summation efficacy was critically dependent on the spatial location and arrival timing between synaptic inputs at the dendrite, and was attributed to a local modulation of dendritic channels following LTP induction. Furthermore, these spatiotemporally specific modifications in the EPSP summation linearity differentially enhanced the coincidence detection and temporal integration functions at the distal and proximal dendrites, respectively. Thus, our findings underscore a notion that the activity-induced plasticity of dendritic functions, together with synaptic plasticity, constitutes an integral part of activity-dependent information processing and storage in neural circuits.