Local changes in potassium ions modulate dendritic integration

Abstract

During neuronal activity the extracellular concentration of potassium ions ([K+]o) increases substantially above resting levels, but it remains unclear what role these [K+]ochanges play in dendritic integration of synaptic inputs. We used mathematical formulations and biophysical modeling to explore the role of activity-dependent K+changes near dendritic segments of a visual cortex pyramidal neuron, receiving synaptic inputs tuned to stimulus orientation. We found that the fine-scale spatial arrangement of inputs dictates the magnitude of [K+]ochanges around the dendrites: Dendritic segments with similarly-tuned inputs can attain substantially higher [K+]oincreases than segments with diversely-tuned inputs. These [K+]oelevations 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+]ochanges around dendrites may act as a “volume knob” that determines the impact of synaptic inputs on feature-tuned neuronal firing.