The Action Potential Clamp as a Test of Space-Clamp Effectiveness - The Lettvin Analog Axon

For a Lettvin analog axon, in which spurious currents due to inadequate space clamp are absent, the action potential clamp technique accurately reproduces the original stimulating current. The action potential generated for the first phase of the experiment is stored digitally. When this action potential waveform is used for the voltage clamp phase of the experiment, digital noise in the resultant current record is a factor of ten smaller than that of the reproduced current record. The requirement of rapid transition between the two experimental components for such experiments with squid giant axon is examined.