Figure 2.

Depolarization from hyperpolarized membrane potentials triggered burst firing in a subset of MHb neurons. A, Step depolarization triggered burst firing from a resting V_m of −63 mV. With constant current injection to a V_m of −58 mV, step depolarization triggered initial burst firing followed by tonic firing. With constant current injection to a V_m of −52 mV, step depolarization triggered solely tonic firing. B, Ramp depolarization from a V_m <−60 mV triggered initial burst firing in 30 of 152 MHb neurons (19.7%). Tonic firing was observed as the V_m depolarized above approximately −55 mV. C, Bursting was observed when the V_m was −68 mV before ramp depolarization but was abolished with constant current injection to −57 or −53 mV before the ramp.