Sydney Cash and Rafael Yuste
Department of Biological Sciences, Columbia University
Understanding how neurons integrate thousands of inputs distributed over complex dendritic trees is essential for a detailed knowledge of neuronal information processing. We characterized the effects of dendritic morphology on summation of excitatory inputs using simultaneous microiontophoresis of glutamate at two positions on the dendritic tree of cultured hippocampal neurons. For small depolarizations spatial summation was linear regardless of input position. For large inputs on the same dendritic branch or on fine branches of the apical dendrite there was a small, albeit significant, sublinearity in the summation. This sub-linearity arose primarily from dendritic K conductances. Thus, although inputs at particular locations can sum sub-linearly, complex dendritic morphologies ensure overall linear summation, enabling independent processing of multiple synaptic events.