Hyperpolarization activated cation channels of the HCN gene family such as HCN2, contribute to spontaneous rhythmic activity in both heart and brain. HCN2 is a member of a family of pacemaker channels activated by hyperpolarization and regulated by cyclic nucleotides. HCN1 and HCN2 play an important role for motor learning and neuronal integration by cerebellar Purkinje cells; as well as, shaping autonomous activity of single neurons and the periodicity of network oscillations. HCN2 is highly abundant in mamillary bodies, pontine nucleus, ventral cochlear nucleus, and nucleus of the trapezoid body. HCN4 is another member of the family of hyperpolarization activated and cyclic nucleotide gated channels. HCN currents have been linked to pacemaker activity in the heart and brain, resting potential control, as well as neuronal plasticity. It has been shown that HCN4 channels function as receptors for sour taste, and are associated with pacemaker potential generation in the sinoatrial node.