Dendritic integration is a fundamental process of neuronal operation. Distal apical dendrites of neocortical layer 5 pyramidal neurons are capable to generate a regenerative dendritic calcium spike that propagates to the axo-somatic region to trigger action potentials. Direct electrical recordings from distal apical dendrites recently demonstrated that deep layer interneurons can block the initiation of dendritic calcium spikes in L5 pyramidal neurons.

However, the role of superficial interneurons in controlling dendritic integration remains to be elucidated. Neurogliaform cells constitute a class of GABAergic interneurons that has been shown, in contrast to other GABA-releasing neurons, to evoke combined GABAA and GABAB receptor-mediated responses in neighboring pyramidal neurons in response to a single action potential elicited in NGFCs. Further, they have been shown to release GABA into the extracellular space providing non-specific input to neighboring neurons. Using paired recordings we show that neurogliaform cells can directly inhibit dendritic regenerative events in layer 5 pyramidal neurons. Superficial interneurons are, therefore, ideally suited to control dendritic excitability and act as veto-neurons inhibiting forward-propagation of dendritic spikes and neuronal output.