Background and aims: Laser-evoked potentials (LEPs) are considered the best neurophysiological method to assess the function of thermonociceptive pathways. A promising alternative could be the recording of contact cool-evoked potentials (CEPs). Our aim was to compare LEPs and CEPs in patients with a suspected dysfunction of the thermonociceptive pathways. 
Methods: 21 patients (10 males; 49±9 years old) suspected of thermonociceptive pathways dysfunction, based on clinical examination, were tested. LEPs were obtained using a temperature-controlled CO2 laser (>1000°C/s, 30 stimuli, 60°C, 100ms, 28mm2). CEPs were obtained using a high-speed cooling device (300°C/s, 30 stimuli, 20°C, 100ms, 120mm2). Stimuli were delivered to the left and right foot dorsa. Vibrotactile somatosensory-evoked potentials (SEPs) were also recorded using a vibrotactile transducer (30 stimuli, 300Hz, 100ms). LEPs, CEPs and SEPs were recorded in separate blocks (randomized order across patients).
Results: There was a significant positive correlation between the N2-P2 peak-to-peak amplitudes of LEPs and CEPs (r=0.60, p< .0001) but no significant correlation with the amplitudes of SEPs. The N2 and P2 peaks latencies did not correlate significantly across modalities.
Conclusions: The positive correlation of CEP and LEP but not SEP amplitudes recorded in patients with suspected thermonociceptive dysfunction may be explained by the fact that LEPs and CEPs are both dependent on the state of peripheral Aδ-fibers and their spinothalamic projections, while SEPs depend mainly on the state of large-diameter Aβ-fibers and their lemniscal projections. These findings suggest that CEPs might become an alternative to LEPs for assessing the functional status of the thermonociceptive pathways.

CONTACT COOL EVOKED BRAIN POTENTIALS CORRELATE WITH LASER BUT NOT WITH VIBROTACTILE EVOKED BRAIN POTENTIALS IN PATIENTS WITH SUSPECTED DYSFUNCTION OF THE THERMONOCICEPTIVE PATHWAYS