Orientation preferences of excitatory and inhibitory neurons. A network of excitatory and inhibitory exponential integrate-and-fire neurons with plastic feedforward inputs, where the recurrent connections from excitatory to excitatory and excitatory to inhibitory connections are plastic under the voltage-triplet STDP rule. After learning, the excitatory neurons which have the same orientation preference have a high chance of being bidirectional connected, as seen in experimentally. On the other hand, inhibitory neurons receive inputs from excitatory neurons with different orientation preferences, consistent with recent experimental results. After learning, receptive fields of the excitatory neurons (black) and the inhibitory neurons (blue). Note that the inhibitory neurons develop broader and more unspecific receptive fields than excitatory neurons.