PT - JOURNAL ARTICLE AU - Jack Waters AU - Fritjof Helmchen TI - Boosting of Action Potential Backpropagation by Neocortical Network Activity <em>In Vivo</em> AID - 10.1523/JNEUROSCI.2933-04.2004 DP - 2004 Dec 08 TA - The Journal of Neuroscience PG - 11127--11136 VI - 24 IP - 49 4099 - http://www.jneurosci.org/content/24/49/11127.short 4100 - http://www.jneurosci.org/content/24/49/11127.full SO - J. Neurosci.2004 Dec 08; 24 AB - Action potentials backpropagate into the dendritic trees of pyramidal neurons, reporting output activity to the sites of synaptic input and provoking long-lasting changes in synaptic strength. It is unclear how this retrograde signal is modified by neural network activity. Using whole-cell recordings from somata, apical trunks, and dendritic tuft branches of layer 2/3 pyramidal neurons in vivo, we show that network-driven subthreshold membrane depolarizations (“up states”) occur simultaneously throughout the apical dendritic tree. This spontaneous synaptic activity enhances action potential-evoked calcium influx into the distal apical dendrite by promoting action potential backpropagation. Hence, somatic feedback to the dendrites becomes stronger with increasing network activity.