CEPs can be a complementary tool to the recording of LEPS for assessing the function of small-diameter Aδ-fibers and the spinothalamic tract.

Thermosensation is crucial for humans to probe the environment and detect threats arising from noxious heat or cold. Over the last years, EEG frequency-tagging using long-lasting periodic radiant heat stimulation has been proposed as a means to study the cortical processes underlying tonic heat perception. This approach is based on the notion that periodic modulation of a sustained stimulus can elicit synchronized periodic activity in the neuronal populations responding to the stimulus, known as a steady-state response (SSR). In this paper, we extend this approach using a contact thermode to generate both heat-and coldevoked SSRs. Furthermore, we characterize the temporal dynamics of the elicited responses, relate these dynamics to perception, and assess the effects of displacing the stimulated skin surface to gain insight on the heat-and cold-sensitive afferents conveying these responses. Two experiments were conducted in healthy volunteers. In both experiments, noxious heat and innocuous cool stimuli were applied during 75 seconds to the forearm using a Peltier-based contact thermode, with intensities varying sinusoidally at 0.2 Hz. Displacement of the thermal stimulation on the skin surface was achieved by independently controlling the Peltier elements of the thermal probe. Continuous intensity ratings to sustained heat and cold stimulation were obtained in the first experiment with 14 subjects, and the EEG was recorded in the second experiment on 15 subjects. Both contact heat and cool stimulation elicited periodic EEG responses and percepts. Compared to heat stimulation, the responses to cool stimulation had a lower magnitude and shorter latency. All responses tended to habituate along time, and this response attenuation was most pronounced for cool compared to warm stimulation, and for stimulation delivered using a fixed surface compared to a variable surface.

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Background Quantitative sensory testing of thermal detection abilities is used as a clinical tool to assess the function of pain pathways. The most common procedure to assess thermal sensitivity, the ‘method of limits’, provides a quick but rough estimate of detection thresholds. Here, we investigate the potential of evaluating not only the threshold but also the slope of the psychometric functions for cold and warm detection. Method A convenience sample of 15 patients with diabetes mellitus (DM) and 15 age‐matched healthy controls (HC) was tested. Thirty brief (100 ms) stimuli of each modality were applied to the volar wrist and foot dorsum. Cold and warm stimuli were delivered with a Peltier thermode and a temperature‐controlled CO2 laser, respectively. Stimulus intensities were dynamically selected using an adaptive Bayesian algorithm (psi method) maximizing information gain for threshold and slope estimation. ROC analyses were used to assess the ability of slopes, thresholds and the combination of both to discriminate between groups. Results Assessment of the slope and threshold of the psychometric function for thermal detection took about 10 min. The ability to detect warmth was not reduced in DM patients as compared to HC. Cold detection performance assessed using slope or threshold parameters separated DM from HC with good discriminative power. Discrimination was further increased when both parameters were used together (93% sensitivity and 87% specificity), indicating that they provide complementary information on patient status. Conclusion The psi method may be an interesting alternative to the classical method of limits for thermal QST. Significance Current QST protocols provide an incomplete and potentially biased estimate of sensory detection performance. We propose a method that estimates the slope and the threshold of the psychometric function, defining heat and cold sensory detection performance, in only a few minutes. Furthermore, we provide preliminary evidence that combining slope and threshold parameters of cold detection performance leads to a better discriminative ability than relying solely on the threshold.

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