Thermal and tactile sensations interact in shaping how we perceive our environment. These interactions rely on the activity of distinct but converging somatosensory pathways and may be altered by aging. In this study, we investigated how innocuous thermal stimulation modulates tactile sensitivity in healthy young and older adults. Mechanical detection thresholds (MDTs) were measured on the dorsal hand using a standardized protocol, while non-painful thermal stimuli were applied as follows: cold (20 °C) and warm (40 °C) either ipsilaterally or contralaterally to the testing site, and a neutral temperature (32 °C) applied only ipsilaterally. Two thermal stimulation methods were used: a localized contact thermode and a global air-based thermal chamber. Results showed that cold stimulation applied ipsilaterally to the tested hand significantly increased MDTs in both age groups, indicating reduced tactile sensitivity. This effect was consistent across stimulation methods, but stronger with the thermode and more pronounced in older adults. Neither warm nor contralateral thermal stimulation produced significant modulation, and neutral temperature had no effect, confirming the specificity of the cold-induced modulation. These findings indicate that cold input inhibits tactile sensitivity in a spatially and modality-specific manner. The absence of contralateral effects supports a segmental, rather than supraspinal, mechanism of thermo-tactile interaction. These results contribute to our understanding of age-related changes in multisensory integration and may inform the development of sensory assessment tools and therapeutic approaches tailored for older individuals.

This study aimed to investigate the role of cutaneous vasodilation in heat pain tolerance during aging. We hypothesized that reduced vasodilation in response to heat would lead to a less efficient heat dissipation, and thus be associated with diminished heat pain tolerance. Due to their efferent role in vasomotor function, we hypothesized that C-fiber functionality would be associated to the efficacy of cutaneous vasodilation. Twenty younger and forty older subjects participated in a 15-min heat pain tolerance test, during which pain ratings were continuously measured, along with skin temperature. Participants could terminate the test at any time if the pain became unbearable. A local thermal hyperemia protocol was conducted to assess cutaneous vasodilation using laser Doppler flowmetry. Warm detection and heat pain thresholds were measured to evaluate small fiber functionality. Older subjects were divided into two groups according to their pain tolerance duration. The older MAX group (n = 22; i.e., 55 %) completed the tolerance test, while the older LOW group did not. Older MAX had preserved cutaneous vasodilation compared to young subjects, whereas older LOW had reduced heat-induced vasodilation. In addition, the skin temperature of older LOW subjects reached a higher level during the pain tolerance test, which was associated to higher pain ratings compared to the two other groups. Older LOW also had higher warm detection threshold, pointing to diminished C-fiber functionality. Reduced cutaneous vasodilation, possibly linked to impaired C-fiber functionality in aging, affects heat pain tolerance due to less efficient heat dissipation.

Background Care procedures for preterm infants can induce stress that may disrupt homeostasis, possibly altering cerebral perfusion or oxygenation. We evaluated the physiological and cerebral oxygenation changes during the routine care of very preterm infants. Methods We analyzed the changes in heart and respiratory rates and in systemic and regional cerebral oxygen saturation of 27 very preterm infants, defining three care periods of 5 min each: 30 min before care, 30 min during care, and 30 min after care. Mean maximum and minimum values for each parameter during the defined care periods were compared by analysis of variance (ANOVA) for repeated measures. Results The mean heart rate was significantly higher during (160 ± 8 bpm) than before and after care (151 ± 21 and 151 ± 6 bpm, respectively). The mean respiratory rate decreased during care and increased afterward: 44 ± 2.2, 40.6 ± 3.2, and 46.7 ± 3.4 cycles/min, respectively (p < 0.05). The mean regional cerebral oxygen and systemic saturation did not vary significantly. Mean minimum and maximum values for each parameter varied during and after care as compared with before care (all p < 0.01). The mean minimum cerebral and systemic saturation was lower after care than before care: 59 ± 8 % versus 63 ± 8 % and 83 ± 3 % versus 90 ± 7 %, respectively (p < 0.05). Conclusions During routine care procedures for very preterm infants, the change in physiological parameters suggested an autonomic stress reaction. Cerebral desaturation may occur during and after the care of such infants and call for specific attention to better support the physiological and cerebral well-being of these infants during standard care procedures.

Aim: To compare the effectiveness of two methods for measuring cold detection thresholds in screening for temperature-perception deficits in elderly individuals with type 2 diabetes (T2 diabetes). Methods: Cold threshold measurements were performed on seven body regions of participants with diabetes without neuropathy (n = 30; mean age, 70.9 f 6.5 years) and healthy participants (n = 73; mean age, 68 f 5 years). Two protocols applying the Levels Method were used: the first used skin temperature as the starting point; the second used 40 degrees C. Results: Cold detection thresholds were significantly higher in subjects with diabetes, particularly on the foot. For CDT TSk, values were-2.22 f 1.91 degrees C in non-diabetic and-3.27 f 3.33 degrees C in diabetic groups (p = 0.023); for CDT 40, values were-9.82 f 3.5 degrees C and-12.18 f 4.5 degrees C (p = 0.003). However, after adjusting for age, the group effect on cold threshold with skin temperature as baseline disappeared. Sensory screens showed that the Area Under Curve of the method using a 40 degrees C baseline was 0.69 (p = 0.002). Conclusion: Measuring the cold detection threshold on the foot with a 40 degrees C baseline is more effective than using skin temperature as a baseline for screening sensory alterations in elderly subjects with type 2 diabetes before neuropathy onset. Significance: These findings highlight the importance of selecting the appropriate cold detection threshold method for elderly individuals with type 2 diabetes. The optimal method can facilitate early identification of sensory changes, minimizing complications and improving overall well-being.

INTRODUCTION/AIMS:Limitations exist in evaluating mechanical detection thresholds (MDTs) due to a lack of dependable electronic instruments designed to assess Aβ fibers and measure MDTs across different body areas. This study aims to evaluate the test-retest and inter-rater reliability of the cutaneous mechanical stimulator (CMS), an electronic tactile stimulator, in quantifying MDTs. METHODS:Using a test-retest design, participants underwent assessments of MDTs using Semmes-Weinstein monofilaments (SWM) and the CMS. This study included 27 healthy volunteers (mean age 24.07 ± 3.76 years). Two raters assessed MDTs using SWM and the CMS at two stimulation sites (the left hand and foot) in two experimental sessions approximately 2 weeks apart. RESULTS:MDTs using SWM and the CMS showed excellent reliability on the hand (intraclass correlation coefficient [ICC] = .84) and foot (ICC = .90). A comparison of results obtained at the two sessions showed that MDTs on the hand displayed good reliability for both SWM (ICC = .63) and the CMS (ICC = .73), whereas MDTs on the foot displayed fair reliability for SWM (ICC = .50) and the CMS (ICC = .42). MDTs exhibited good inter-rater reliability with SWM (ICC = .66) and excellent inter-rater reliability with the CMS (ICC = .82) on the hand, as well as showing fair inter-rater reliability with SWM (ICC = .53) and good inter-rater reliability with the CMS (ICC = .60) on the foot. DISCUSSION:The CMS showed superior inter-rater reliability, indicating its potential as a valuable tool for assessing tactile sensitivity in research and clinical settings.

Objective In this study, we compared two working memory conditions to study the analgesic effect of a distraction in elderly vs young people and the effect of pain on performance on the distracting task. Methods Younger (n=27) and older (n= 34) subjects performed 1- and 2-Back working memory tasks, representing low and high cognitive loads, respectively. Infrequent, brief hot nociceptive and cold non-nociceptive stimulations were delivered 100 ms before visual N-Back stimuli. Contact heat-evoked and cold-evoked potentials (N2P2 component) were analyzed in the absence of cognitive tasks and during the N-Back tasks. We compared the pain and cold intensity ratings and reaction times in trials preceded by nociceptive and cold stimulations and in trials not preceded by thermal stimulations between groups and between N-Back conditions. Results In both groups, performing the 1- and 2-Back working memory tasks reduced the perceived intensity of nociceptive and cold stimuli. In elderly subjects performing 2-Back memory tasks, response times to trials after nociceptive stimulation were longer than those to trials after cold or non-stimulation. By contrast, thermal stimulations had no effect on reaction times in young subjects. The amplitude of the N2P2 component was lower in the older than in the younger group in the absence of a cognitive task. In the older group, N-Back tasks had no effect on the N2P2 amplitude, whereas they reduced N2P2 amplitude in the young. Conclusion Distraction analgesia is preserved in elderly subjects. However, this successful pain modulation seems to be accompanied by performance costs in the distracting tasks.

Objective: We aimed to determine the ability of an innovative device, the Cutaneous Mechanical Stimulator (CMS), to evaluate touch sensory pathways in Human.Methods: Two experiments were conducted in 23 healthy volunteers aged 20-30 years. In the first, mechanical detection thresholds (MDTs) were assessed using Semmes-Weinstein monofilaments and the CMS. In the second experiment, touch-evoked potentials (TEPs) elicited by tactile stimulation of the CMS on the left hand dorsum and left foot dorsum were recorded. Electroencephalographic (EEG) data were recorded at each cutaneous stimulation site in blocks of 20 tactile stimulations delivered by the CMS. The data were segmented into 1000-ms epochs.Results: MDTs measured by monofilaments and by the CMS were equivalent. Analyses of TEPs showed N2 and P2 components. The latencies of the N2 components on the hand dorsum and foot dorsum resulted in an estimated average conduction velocity of about 40 m.s-1, within the range of Ab fibers.Conclusions: These findings showed that the CMS could assess touch sensory pathways in young adults. Significance: The CMS can offer new research perspectives, as this device allows easy assessment of the MDT and enables estimation of fiber conduction velocities after tactile stimulation by the device synchronized with EEG recordings. & COPY; 2023 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

We aimed to explore the link between local vasodilation and pain perception in elderly subjects, testing the hypothesis that altered local cutaneous blood flow participates in the decrease in pain tolerance with age. Sixty-eight young and 83 older participants performed a pain tolerance test in which they hold their hand in an airtight box in which air temperature was regulated at 65 °C until the pain became unbearable. Participants continuously estimated pain intensity. Skin temperature and local blood flow in the box-exposed hand were continuously monitored. In the young group, 97

Immersive virtual reality (VR) is a promising tool to reduce pain in clinical setting. Digital scripts displayed by VR disposals can be enriched by several analgesic interventions, which are widely used to reduce pain. One of these techniques is hypnosis induced through the VR script (VRH) which is facilitated by immersive environment and particularly efficient even for low hypnotizable patients. The aim of this study is to assess the efficacy of a VRH script on experimentally induced cold pain perception (intensity and unpleasantness) and physiological expression. 41 healthy volunteers had been recruited in this within-subjects study. They received 9 stimulations of 20 s (3 non-nociceptive cold; 3 low nociceptive cold and 3 highly nociceptive cold) during a VRH session of 20 min (VRH condition) or without VRH (noVRH condition). Physiological monitoring during the cold pain stimulation protocol consisted of recording heart rate, heart rate variability and respiratory frequency. Maximum cold pain intensity perception, measured through the visual analog scale (VAS) on 10, was of 3.66 ± 1.84 (VAS score/10) in noVRH condition and 2.46 ± 1.54 in VRH (Wilcoxon, p < 0.0001). Considering pain unpleasantness perception, 3.68 ± 2.06 in noVRH and 2.21 ± 1.63 in VRH (Wilcoxon, p < 0.0001). Hypnotizability negatively correlated with the decrease in VAS intensity from noVRH to VRH (Spearman r = −0.45; p = 0.0038). In our sample, we found that 31/41 volunteers (75.6%) displayed a reduction of more than 10% of their VAS pain intensity and unpleasantness scores. Trait anxiety was the best predictor of the VRH responders, as well as heart rate variability. In addition, respiratory rate was diminished under VRH in every subgroup. VRH is an effective tool to reduced pain intensity and unpleasantness in a vast majority of healthy subjects. We further indicate in this study that heart rate variability parameter RMSSD (root mean square of successive differences) is a good predictor of this effect, as well as anxiety as a personality trait (but not state anxiety). Further studies are expected to determine more precisely to whom it will be the most useful to offer tailored, non-pharmacological pain management solutions to patients.

Objective: To evaluate the activity of cold A8-type fibers to thermal stimuli above human skin temperature (i.e., >32 degrees C).Methods: Twenty young adults aged 20-24 years participated in this study. The cold-detection threshold was measured from a basal temperature of 40 degrees C using an adaptive staircase method with high-speed cooling ramps (170 degrees C/s). A total of 150 stimulations at 36 degrees C, 32 degrees C, 28 degrees C, 24 degrees C, 20 degrees C, 16 degrees C, 12 degrees C, 8 degrees C, 4 degrees C and 0 degrees C (15 each) were performed. After each stimulation, subjects estimated the intensity of cold sensation using a visual analog scale, and evoked potentials were recorded.Results: The average cold-detection threshold was 35 degrees C (SD = 1.8). Regardless of the stimulation temperature, subjects reported a cooling sensation. Interestingly, reported increments in sensation were prominent for stimulation temperatures between 32 degrees C and 20 degrees C, but below this latter temperature sensations varied only very slightly. Evoked potential recordings revealed that decreasing temperature stimuli from a baseline of 40 degrees C induced a previously unreported N2P2 component with a mean N2 peak latency of 275 ms (SD = 13.1). The peak-to-peak amplitude of the N2P2 complex increased as the intensity of the cooling stimulation increased, exhibiting a profile comparable to subject-perceived intensity, namely, a major increase up to 20 degrees C, followed by a plateau to 0 degrees C.Conclusions: The cool sensations reported by subjects were likely conveyed by A8 fibers rather than by slow-conducting C fibers. Moreover, our rapid stimulation technique starting from a high temperature (40 degrees C) was capable of a) generating cold sensations at stimulation temperatures between 36 degrees C and 32 degrees C, and b) revealing the optimal activation range of A8 fibers (20 degrees C-28 degrees C). Any decrease in temperature below this range did not result in a significant increase in sensation and thus probably did not evoke a significant increase in A8 fiber activity. Significance: The regular assessment of cold sensation in peripheral neuropathies (i.e., with temperatures below 32 degrees C), could be completed by investigating cold-detection thresholds at temperatures ranging from 40 degrees C to 32 degrees C. Indeed, the absolute threshold of cold perception appears to start at 35 degrees C. Changes in the activation threshold of cold fibers were more easily detectable at this level.(c) 2021 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

BACKGROUND:Virtual reality hypnosis (VRH) is a promising tool to reduce pain. However, the benefits of VRH on pain perception and on the physiological expression of pain require further investigation. OBJECTIVE:In this study, we characterized the effects of VRH on the heat pain threshold among adult healthy volunteers while monitoring several physiological and autonomic functions. METHODS:Sixty healthy volunteers were prospectively included to receive nociceptive stimulations. The first set of thermal stimuli consisted of 20 stimulations at 60°C (duration 500 milliseconds) to trigger contact heat evoked potentials (CHEPs). The second set of thermal stimuli consisted of ramps (1°C/second) to determine the heat pain threshold of the participants. Electrocardiogram, skin conductance responses, respiration rate, as well as the analgesia nociception index were also recorded throughout the experiment. RESULTS:Data from 58 participants were analyzed. There was a small but significant increase in pain threshold in VRH (50.19°C, SD 1.98°C) compared to that in the control condition (mean 49.45°C, SD 1.87; P<.001, Wilcoxon matched-pairs signed-rank test; Cohen d=0.38). No significant effect of VRH on CHEPs and heart rate variability parameters was observed (all P>0.5; n=22 and n=52, respectively). During VRH, participants exhibited a clear reduction in their autonomic sympathetic tone, as shown by the lower number of nonspecific skin conductance peak responses (P<.001, two-way analysis of variance; n=39) and by an increase in the analgesia nociception index (P<.001, paired t-test; n=40). CONCLUSIONS:The results obtained in this study support the idea that VRH administration is effective at increasing heat pain thresholds and impacts autonomic functions among healthy volunteers. As a nonpharmacological intervention, VRH has beneficial action on acute experimental heat pain. This beneficial action will need to be evaluated for the treatment of other types of pain, including chronic pain.

•Thermal stimuli with decreasing intensity from 40 °C elicit a cool sensation, with a detection threshold of 35 °C.•Thermal stimuli elicit evoked potentials with an N2P2 component whose latency is within the Aδ fiber range and amplitude is positively correlated with cooling amplitude.•Cold temperature discrimination starts to increase below 32 °C, peaks at 20 °C, and then decreases for temperatures below 16 °C.

Abstract Introduction: Early neuronal processing of thermal noxious information relies mostly on molecular detectors of the transient receptor potential family expressed by specific subpopulation of sensory neurons. This information may converge to second-order wide-dynamic-range (WDR) neurons located in the deep layer of the dorsal horn of the spinal cord. Method: Using a micro-Peltier thermode thermal contact stimulator II delivering various cold and hot noxious stimulations, we have characterized the extracellular electrophysiological responses of mechanosensitive WDR neurons in anesthetized adult male and female Wistar rats. Results: Most of the WDR neurons were activated after hot and cold noxious stimulations, at mean temperature thresholds corresponding to 43 and 20°C, respectively. If the production of action potential was not different in frequency between the 2 thermal modalities, the latency to observe the first action potential was significantly different (cold: 212 ms; hot: 490 ms, unpaired Student t-test: t = 8.041; df = 32; P < 0.0001), suggesting that different fiber types and circuits were involved. The temporal summation was also different because no facilitation was seen for cold noxious stimulations contrary to hot noxious ones. Conclusion: Altogether, this study helps better understand how short-lasting and long-lasting hot or cold noxious stimuli are integrated by mechanosensitive WDR neurons. In our experimental conditions, we found WDR neurons to be nociceptive specific for C-fiber–mediated hot stimuli. We also found that cold nonnoxious and noxious information, triggered at glabrous skin areas, are likely taken in charge by A-type sensory neurons. This study will be helpful to establish working hypothesis explaining the thermal pain symptoms displayed by animal models and patients in a translational extent.

It has been proposed that agency disorders found in schizophrenia rely on aberrant processing of prediction error. Overreactivity to nonpertinent prediction errors may lead to the attribution of one's own actions to an external source. When applied to perception, this could explain hallucinations. However, experiments in motor control or perception have mainly suggested deficient prediction errors. Using a novel approach based on the manipulation of temporal delays, 23 patients with schizophrenia, 18 patients with bipolar disorder, and 22 healthy participants performed a pointing task with a haptic device that provided haptic feedback without or with delays, which were processed consciously (65 ms) or unconsciously (15 ms). The processing of prediction errors was measured via the adaptation of the hand trajectory, that is, the deceleration in anticipation of the surface, and its modulation as a function of recent history (stable or unstable sensory feedback). Agency was evaluated by measuring the participants' feeling of controlling the device. Only patients with schizophrenia reported a decrease in the feeling of control following subliminally delayed haptic feedback and adapted deceleration durations following subliminally delayed haptic feedback. This effect was correlated with positive symptoms. The overreactivity to subliminal delays was present only when delays occurred repeatedly in an unpredictable way, that is, with a volatile distribution. The results suggest that small temporal uncertainties that should be held as negligible, trigger an aberrant overreactivity which could account for hallucinations and alterations of the patients' conscious feeling of control. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Noise and high light illumination in the neonatal intensive care unit (NICU) are recognized as stressors that could alter the well-being and development of vulnerable preterm infants. This prospective observational study evaluated the pain behaviours of very preterm infants (VPIs) to sound peaks (SPs) and light levels variations (LLVs) in the NICU. We measured spontaneously occurring SPs and LLVs in the incubators of 26 VPIs over 10 h. Their behavioural responses were analysed through video recordings using the "Douleur Aigue du Nouveau-né" (DAN) scale. We compared the maximum DAN scores before and after environmental stimuli and the percentage of VPIs with a score ≥ 3 according to the type of stimuli. A total of 591 SPs and 278 LLVs were analysed. SPs of 5 to 15 dBA and LLVs significantly increased the maximum DAN scores compared to baseline. The occurrence of DAN scores ≥ 3 increased with both stressors, with a total of 16% of SPs and 8% of LLVs leading to quantifiable pain behaviour. Altogether, this study shows that VPIs are sensitive to SPs and LLVs, with a slighter higher sensitivity to SPs. The mechanisms leading to pain behaviours induced by noise and light changes should be evaluated further in the context of VPIs brain development. Our results provide further arguments to optimize the NICU sensory environment of neonatal units and to adapt it to the expectations and sensory abilities of VPIs.

Purpose: The sense of vision is responsible for 90% of the information obtained by the motorist. Improvement in binocular visual acuity (VA) and visual field (VF) achieved after strabismus surgery could have beneficial effects on driving. Our study sought to identify functional improvements (VA and VF) and improvements in driving ability following strabismus surgery. Methods: In a prospective cohort study, the following parameters are analyzed before and 3 months after strabismus surgery: simulated driving performance (including eye movements and actions on vehicle control), binocular VA, binocular VF, and self-confidence during driving. Results: Twenty patients participated in the study. The mean preoperative logMAR binocular VA and stereopsis do not significantly differ from the postoperative. The mean Esterman VF score increases from 91.3 (±17.2) preoperatively to 96.9 (±13.9) postoperatively (P = 0.045). The mean self-confidence directed at driving scores decreases from 20.5 (±10.3) points before surgery to 11.0 (±6.0) points after surgery (P < 0.001). The distance at which the road signs are identified is significantly higher after surgery. The average speed of the vehicle and the speed near the targets (30 m) increase significantly after strabismus surgery. A significant decrease in ocular movements near targets is also observed. The number of brake pedal depressions and the rate of brake pedal depressions slightly decrease after surgery. Conclusions: This study demonstrates the potential beneficial effects of strabismus surgery on driving ability, with significant improvements in self-confidence during driving, VF, and driving on a simulator. Translational Relevance: This was the first study to use a driving simulator in strabismus.

Purpose The bioheat transfer equation predicts temperature distribution in living tissues such as the skin. This study aimed at psychophysically validating this model in humans. Methods Three experiments were performed. In the first, participants were asked to judge the thermal intensity of stimuli with combinations of intensity and duration that yielded, according to the model, identical temperatures at the thermoreceptor's depth. In experiment 2, participants' thermal detection thresholds for stimuli of different durations were measured to verify whether these thresholds correspond, according to the model, to equivalent temperatures at the thermoreceptor's location. In experiment 3, an alternative forced choice method was used, in which subjects indicated which of the two consecutive thermal stimulations was more intense. Results The model predicted results that agreed with subjects' perceptions. Participants judged stimuli of different combinations of intensities and durations yielding identical temperature at the receptor level as having equivalent intensity. Moreover, although cold detection thresholds for stimuli of different durations differed for temperatures of the stimulating probe, stimulations using the model's parameters showed equivalence at the depth of the thermal receptors. Furthermore, stimuli with temperature/duration combinations for which the model predicts temperature equivalence at the depth of the receptors corresponded to subjective equalization. Conclusion These findings indicate that heat transfer models provide good estimates of temperatures at the thermal receptors. Use of these models may facilitate comparisons among studies using different stimulation devices and may facilitate the establishment of standards involving all stimulation parameters.

OBJECTIVEThis study used high-speed cooling of the skin and exact control of stimulus duration to measure the cold detection threshold in healthy participants. The objective was to compare the method of limits, in which the temperature is slowly and gradually increased/decreased until the subject perceives the stimulation, and the method of levels, in which the subject must detect brief thermal stimulations close to the threshold of perception.METHODSTwenty healthy volunteers (nine women, 11 men) aged 20-30 years participated in the study. The method of limits and method of levels were performed in all subjects in a counterbalanced order. Four cold detection thresholds were measured with the method of levels, with a temperature ramp of 300°C/sec and stimulus durations of 50 ms, 100 ms, 300 ms, and 500 ms. Three thresholds were measured with the method of limits, with temperature ramps of 1°C/sec, 2°C/sec, and 4°C/sec.RESULTSOn average, the cold detection thresholds were -0.47°C below skin temperature with the method of levels and -1.67°C the method of limits. Interindividual variability was significantly lower with the method of levels than with the method of limits.CONCLUSIONSThese results suggest that the method of levels is more accurate than the method of limits for measuring cold detection threshold. The improvement of cold detection threshold measurement may provide new perspectives to more precisely assess the function of A-delta fibers and the spino-thalamic pathway.