The integrated response of a population of neurones during conditioning results in long-term (days) changes of specific membrane currents within identified neurones. Prolonged elevation of intracellular calcium during conditioning causes a persistent increase of excitability by reducing K+ currents (IA and probably ICa2+-K+) in the membranes of identified somata. This Ca2+-mediated reduction of K+ currents, which encodes a learned stimulus association is thought to involve changes of Ca2+-calmodulin-dependent phosphorylation of distinct membrane proteins. These changes are contrasted with the short-term regulation of currents by neurohormones during altered behavioural states such as arousal.

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