Cells that exhibit sub-threshold oscillations will exhibit phase-dependent rheobase. If the current step onset co-insides with the peak of a sub-threshold oscillation (cell is closer to the firing threshold), a smaller current will be needed to elicit a spike. Conversely, if the step onset co-insides with the trough of the oscillation (further away from the threshold), a larger current will be necessary to produce a spike. Using different delays before onset and repeating the current injections can be used to find the current that will guarantee that a spike will be produced regardless of sub-threshold oscillation phase.