Pyramidal neurons often connect to inhibitory cells that project back to the dendrites the
pyramidal neurons. This recurring microcircuit, the Martinotti loop, is anatomically poised to
combine the input of the deeper cortical layers with what impinges on the superficial layers.
We have constructed a simple computational model that captures three salient
electrophysiological features of this system: nonlinear dendritic integration in the dendritic tuft
of pyramidal cells [1,2], facilitating excitatory synapses, and saturating frequency-dependent
disynaptic inhibition . We then analyzed the input-output properties of the Martinotti loop,
imbedded in a balanced-state network. Our simulations show a direction-dependent
frequency filtering of information, which requires dendritic activity and short-term plasticity.
We contrast our results with signatures of feedback and feedforward cortical processing in vivo .
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 T.K. Berger, G. Silberberg, R. Perin, H. Markram PLoS biology 8(9):e1000473 (2010).
 T. van Kerkoerle, M.W. Self, B. Dagnino, M.A. Gariel-Mathis, J. Poort, C. van der Togt, et al. Proceedings of the National Academy of Sciences 111(40):14332-14341 (2014).