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Fig. 4 | Neural Development

Fig. 4

From: Does experience provide a permissive or instructive influence on the development of direction selectivity in visual cortex?

Fig. 4

A feed-forward model with Hebbian plasticity and increasing feed-forward inhibition can, in principle, develop direction selectivity in an instructive manner. a Schematic of the feed-forward model [37]. An array of LGN neurons with a broad array of different position preferences and response latencies provide input to a cortical excitatory neuron and a feed-forward cortical inhibitory neuron. The cortical inhibitory neuron provides input to the excitatory neuron. The picture shows an immature network that has a slight (subthreshold) bias for downward motion (darker LGN cells indicates slightly stronger weight). Connections from LGN to the cortical excitatory neuron undergo spike-timing-dependent plasticity, while the synapse from the cortical inhibitory neuron onto the cortical excitatory neuron increases with each bout of stimulation, forcing competition among the inputs [38]. b Responses from the naïve model cortical neuron and LGN neurons to upward and downward stimuli. Each row of LGN cells responds to stimuli at a particular position, with varying latencies. Each black square represents the spiking activity of a single LGN cell. In the middle of the stimulus, the 5 LGN cells along each diagonal are activated simultaneously, allowing the cortical excitatory neuron to fire. c Connections after hundreds of bidirectional stimulation events. The increasing inhibition has forced the cortical excitatory neuron to develop selectivity for downward motion; the LGN inputs that support upward motion (the direction opposite the initial bias) are eventually weakened, because they do not drive the cell after the feed-forward inhibition has developed to full strength. d After training, the cortical neuron responds to stimulation in the downward direction exclusively. Stimulation with downward motion at the appropriate speed (∆d/∆t) will cause the 5 cells that comprise the diagonal to be activated simultaneously, providing strong drive to the cortical neuron. Stimulation with upward motion activates the same 5 LGN cells, but asynchronously, such that they do not drive the cortical cell. Adapted from [37, 39]

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