Somatosensory Evoked Potentials Associated With Thermal Activation of Type ii Aδ Mechanoheat Nociceptive Afferents

Abstract

We evaluated evoked potentials (EPs) to noxious contact heat pulses delivered to hairy skin of healthy adults. Heat pulses from an adapting temperature of 34°C to a target temperature of 52°C. produced two scalp positive waves. The first peaked at 44° to 45°C (~ 500ms following stimulus onset), while the second peaked ~ 300ms following the 52°C heat pulse (~ 1 s after stimulus onset). The first positive wave was absent from an adapting temperature of 39°C, suggesting loss of synchronized activation of warm and, or low threshold mechanothermal afferents. The second EP was observed following stimulation from both adapting temperatures and was associated with subjective report of first pain. Latency difference of the pain EP from arm and leg were consistent with conduction in A$dL nociceptive afferents (~ 10 ms). EPs to painful contact thermal stimuli may be of value in the evaluation of small fiber peripheral neuropathies and assessment of altered pain states.

Key Words:

• Pain evoked potentials
• contact heat pain
• conduction velocity
• first pain
• small fiber peripheral neuropathy