P37 latency mismatch between lateral and midline potentials is influenced by transversal afference.

SUMMARY: P37 cortical peak latency registered on Ci' (lateral) is usually approximately 1 millisecond shorter than Cz' (midline) in lower limb somatosensory evoked potential. At the present time, the underlying mechanism that leads to this mismatch remains unknown. Superficial peroneal nerve, posttibial nerve, and sural nerve somatosensory evoked potentials were obtained from 26 anesthetized individuals by using Ci'-Cc', Cc'-Fpz, and Cz'-Fpz recording montages. P37 latency mismatches between the lateral (Ci'-Cc') and midline (Cz'-Fpz) potentials (P < 0.001) were recorded in superficial peroneal nerve, posttibial nerve, and sural nerve somatosensory evoked potentials; all showed shorter Ci'-Cc' P37 latency (1-1.7 milliseconds). However, in individuals who had minimal or no N37 potential on Cc' recording, the mean P37 latencies of Ci'-Cc' and Cz'-Fpz equalized with the P37 latency of Ci'-Cc' approaching to default Cz'-Fpz value. The data showed that N37 seemed to potentiate the P37 latency difference between Ci-Cc' and Cz'-Fpz recordings. We postulate that N37 may preferentially reflect the dipoles of transversal afference; lack of it thereof suggests poor dipole sources primarily perpendicular to the mesial hemisphere.