Figure 5. Long-range SST projections in LIF network model control slope of contrast sensitivity A.

The probability of SST lateral connections and SST dendritic inhibition strength was varied in the model to identify the source of the slope change with distal SST stimulation.

B. Heat maps showing the average (100 iterations) slope MI of E neurons during distal PV stimulation for varied long-range SST projection probabilities ( p’sST) and SST dendritic inhibition strengths ($\alpha$; see Methods). MI is constant during distal PV stimulation with any lateral connection probability or dendritic inhibition strength. Letters on heatmaps indicate various SST dendritic integration strengths and long-range SST probabilities depicted in D-F.

C. Same as B for distal SST stimulation. Slope changes during distal SST stimulation are largely dependent on SST lateral connection probability (vertical gradient). Slope changes slightly varied with SST dendritic inhibition strength.

D. For high SST lateral projection probability (p’SST =0.8) and high SST dendritic inhibition strength $(\alpha =70\mathrm{M}\mathrm{\Omega }$), distal SST stimulation had larger divisive effects (−0.78 ± 0.05 Ml, median ± MAD) than distal PV stimulation on E neurons across contrasts $(-0.38\pm 0.07\mathrm{M}\mathrm{l};p<1\mathrm{e}-\mathrm{32,1}$-tail Wilcoxon rank-sum test).

E. For high SST lateral projection probability (p’SST = 0.8) and low SST dendritic inhibition strength $(\alpha =40\mathrm{M}\mathrm{\Omega }$), distal SST stimulation has larger divisive effects $(-0.63\pm 0.04\mathrm{M}\mathrm{I})$ than distal PV stimulation on E neurons $(-0.42\pm 0.06;p<1\mathrm{e}-32)$. These effects are smaller than when the strength of SST dendritic inhibition is high (D).

F. For low SST lateral projection probability (p’sst = 0) and high SST dendritic inhibition strength $(\alpha =70\mathrm{M}\mathrm{\Omega })$, distal SST stimulation had a smaller divisive effect (−0.11 ± 0.09 MI) than distal PV stimulation $(-0.41\pm 0.08\mathrm{M}\mathrm{l};p<1\mathrm{e}-30)$, indicating longrange SST projections are essential for eliciting strong divisive effects.