Thalamocortical relay neurons: intrinsic properties determine sleep-related activity. Hyperpolarised membrane potentials activate the hyperpolarisation-activated cyclic nucleotide-gated cation (HCN) channels and de-inactivate T-type Ca 2+ channels. HCN channels then provide a depolarisation that, in turn, triggers a transient current through T-type Ca 2+ channels. The hyperpolarisation-activated cation