Electrochemical potential shifts of ions.

<div><p>During neuronal activity, the extracellular concentration of potassium ions ([K<sup>+</sup>]<sub>o</sub>) increases substantially above resting levels, yet it remains unclear what role these [K<sup>+</sup>]<sub>o</sub> changes play in the dendritic integration of synaptic inputs. We here used mathematical formulations and biophysical modeling to explore the role of synaptic activity-dependent K<sup>+</sup> changes in dendritic segments of a visual cortex pyramidal neuron, receiving inputs tuned to stimulus orientation. We found that the spatial arrangement of inputs dictates the magnitude of [K<sup>+</sup>]<sub>o</sub> changes in the dendrites: Dendritic segments receiving similarly tuned inputs can attain substantially higher [K<sup>+</sup>]<sub>o</sub> increases than segments receiving diversely tuned inputs. These [K<sup>+</sup>]<sub>o</sub> elevations in turn increase dendritic excitability, leading to more robust and prolonged dendritic spikes. Ultimately, these local effects amplify the gain of neuronal input–output transformations, causing higher orientation-tuned somatic firing rates without compromising orientation selectivity. Our results suggest that local, activity-dependent [K<sup>+</sup>]<sub>o</sub> changes in dendrites may act as a “volume knob” that determines the impact of synaptic inputs on feature-tuned neuronal firing.</p></div>