The recent increase in reliable, simultaneous high channel count extracellular recordings is exciting for physiologists and theoreticians, because it offers the possibility of reconstructing the underlying neuronal circuits. We recently presented a method of inferring this circuit connectivity from neuronal spike trains by applying the generalized linear model to crosscorrelograms, GLMCC. Although the GLMCC algorithm can do a good job of circuit reconstruction, the parameters need to be carefully tuned for each individual dataset. Here we present another algorithm using a convolutional neural network for estimating synaptic connectivity from spike trains, CoNNECT. After adaptation to very large amounts of simulated data, this algorithm robustly captures the specific feature of monosynaptic impact in a noisy cross-correlogram. There are no user-adjustable parameters. With this new algorithm, we have constructed diagrams of neuronal circuits recorded in several cortical areas of monkeys. * shinomoto.shigeru.6e@kyoto-u.ac.jpRecently, we developed an estimation method that works well in balancing the conflicting demands of reducing FPs and reducing FNs [11]. The estimation method we call GLMCC (GLM cross-correlation) nonetheless has a shortcoming: the estimation results are sensitive to the model parameters, and therefore the parameters need to be tuned for the spiking data. Here, we develop another algorithm: Convolutional Neural Network for Estimating synaptic Connectivity from spike Trains (CoNNECT). The two premises are that a convolutional neural network is good at capturing the features important for distinguishing among images (in this case, cross-correlograms) and that the cross-correlogram image will contain sufficient information from which to infer the presence of monosynaptic connectivity. This new algorithm is easy to use, and it works robustly with data arising from different cortical regions in non-human primates. The convolutional neural network algorithm has tens of thousands of internal parameters [12][13][14][15]. The parameters are adjusted using hundreds of thousands of pairs of spike trains generated with a large-scale simulation of the circuitry of realistic model neurons. To reproduce large fluctuations in real spike trains, we added external fluctuations to the model neurons in the simulation.CoNNECT provides reasonable inference. It does not, however, give a rationale for why the result was derived, whereas our previous algorithm GLMCC does because it fits an interaction kernel to the cross-correlogram. These methods, therefore, have different strengths and weaknesses