Each model neuron received approximately 50 synapses, roughly 1/100 of those exhibited anatomically. Short range inputs arose from 10% of excitatory neurons within a m radius and 10% of inhibitory neurons within a m radius, thus inhibitory inputs to a column on average had a broader orientation distribution than excitatory inputs. Short range synaptic strengths, , were 15nS (Ex Ex), 2.7nS (Ex In), 35nS (In Ex), 0.5 nS (In In); Ex: excitatory cell, In: inhibitory cell. Thalamocortical synaptic strengths were 2.7nS (Th Ex) and 0.7 nS (Th In). The lower weight values reflect fewer synapses anatomically on inhibitory neurons.
Thalamocortical inputs provided a mild orientation bias to the cells of each column (gaussian in orientation space with or a half-width) which was sharpened by intracortical connections (cf. ). The preferred orientation of the bias to each column (figure 2) was matched to the preferred cortical orientation from an optically recorded map of activity in primary visual cortex of the cat . The total thalamocortical input to each cell was given by a Poisson process for spike times, where the mean firing rate was given by the sum of center and surround contributions. Each regional contribution was , where RF% is the percentage of the cortical receptive field covered by center or surround. is the orientation dependence of the net thalamic input response and is the difference between the stimulus and preferred orientations. Note that thalamic input increases linearly with the log of stimulus contrast.
Cortical receptive fields (i.e., areas receiving direct thalamic input) were square and the visual field position shifted by for each mm shift of cortical position. The central stimulus was by . The surround stimulus covered the full field ( by ) except for the central by region. The central grating orientation was aligned to maximally activate the central orientation domain (colored green in figure 2), with a contrast that varied between 1% and 100%. Surround stimuli were either uniform fields (no surround) or had 100% contrast.
Long range connections were taken to be those longer than m and were made between columns that differed by less than in preferred orientation (see figure 2). Connection probabilities ranged linearly between 0.5% for cell pairs with a difference and 0% at difference. 80% of model long range connections were onto excitatory neurons . Synaptic strengths for long-range excitatory inputs to excitatory and inhibitory neurons were 1.9nS and 2.3nS, respectively.