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Fig. 8. Membrane conductance and the excitability of the cell change concomitantly
after a conditioning spike. The change in membrane resistance was evaluated by
the slope of the V/I plot constructed with data obtained 1
ms after the onset of a series of test current steps of different intensity
(dotted line in inset) applied at different delays after a conditioning spike
in four cells (symbol coded). (A) The increase in slope as a function of the
delay indicates that after the conditioning spike there is an increase in
membrane conductance and a slow return to resting values. (B,C) Change in
spike threshold and spike latency as a function of the slope. Change in
threshold was defined as the difference between the current intensity required
for eliciting a spike when the stimulus was preceded by a conditioning spike
at the given delay minus the current intensity required for eliciting a spike
without a conditioning spike. As the spike threshold and latency decrease with
the slope, the excitability of the cell is reduced by the increase of membrane
conductance caused by the conditioning spike.
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