Figure 1. Changes in threshold (A), supernormality (B) and τ_SD (C) in median sensory and motor axons before, during and after ischaemia for 13 min.

Mean data for 8 subjects (± s.e.m.). The duration of ischaemia is indicated by the filled horizontal bars, starting at 5 min. A, threshold changes measured using 1.0 ms test stimuli normalized to the pre-ischaemic values for median sensory axons (left column) and median motor axons (right column). B, supernormality, expressed as the decrease in threshold for the conditioned potential as a percentage of the unconditioned threshold when the conditioning-test interval was 7 ms. C, τ_SD, calculated off-line using unconditioned test stimuli of 0.1 and 1.0 ms duration. At 60 min (i.e. 42 min after the release of ischaemia), threshold was still significantly greater than the pre-ischaemic level for sensory axons but not for motor axons. Note that the ‘notch’ on the sensory threshold (indicated by the vertical arrow) is associated with appropriate changes in τ_SD and, less obviously, supernormality.