Fluctuations in neuronal electrical activity span orders of magnitude both in temporal and spatial scales. The fine grain scale of ion channels and single neurons is mathematically captured by nonlinear electrical circuits. The behavior of those circuits is robustly regulated by modulating a few feedback loops that combine the dynamic response of neuronal ionic currents. Positive feedback loops play a key role by creating regions of negative conductance that are responsible for neuronal switching and oscillatory behaviors. The role of neuronal negative conductance propagates at the medium scale of neuron networks and at the gross scale of whole body circadian rhythms. At the medium scale, it endows networks with rapid and localized switching capabilities that regulate brain information processing (brain states). At the gross scale, it allows robust circadian fluctuations in neuron electrical activity that influence cellular clock oscillations through calcium-dependent signaling pathways, thus closing a feedback loop essential for free-running molecular oscillations.