Exposure to oscillating magnetic fields influences sensitivity to electrical stimuli. II. experiments on humans

To assess the effect of a magnetic treatment on pain perception, we compared the sensory threshold in 18 healthy volunteers. We determined the threshold by noninvasive electrical stimulation of the tooth pulp and skin before and after exposure to an altered magnetic field of low intensity and to a sham treatment. Five different parameters were recorded: the sensory and pain thresholds for the tooth and the sensory, pain, and tolerance thresholds for the skin. Two hours of exposure to a weak, oscillating magnetic field induced a significant decrease in three parameters (dental sensory and cutaneous pain and tolerance thresholds), whereas the other two parameters showed a similar tendency. When the same subjects were exposed to a sham treatment, only marginal, nonsignificant variations in all parameters were observed. These results represent the first piece of evidence that weak alterations of the magnetic field may induce hyperalgesia in humans. © 1995 Wiley-Liss, Inc.     

背景噪声对人感知声音时间信息的影响

对声音时间信息的分辨在人和动物感知声音信息的过程中至关重要.在自然声环境中,声音信息总处于一定的噪声背景下.文章以间隔探测阈值为指标测定了人对纯音和噪声的间隔探测阈值,以及持续噪声背景对间隔探测阈值的影响.声音信号采用1000～10000 Hz的纯音信号和白噪声信号,声音强度为70 dB SPL.背景噪声为持续白噪声,强度分别为45、55、65 dB SPL.结果表明,对纯音信号,随着背景噪声强度增加,间隔探测阈值有升高的趋势.对噪声信号来说,45、55 dB SPL的背景噪声对噪声信号的间隔探测阈值无显著影响,但65 dB SPL的背景噪声使间隔探测阈值显著升高.研究结果提示,背景噪声能够在一定程度上影响人对声音时间信息的感知,影响的程度与背景噪声的强度有关.     

Comparison perception of singular transcranial magnetic stimuli by subjectively electrosensitive subjects and general population controls

Transcranial magnetic stimulation of the dorsolateral prefrontal cortex by single pulses of varying field intensities was used to measure thresholds of individual perception and motor response in three groups of subjects: subjectively electrosensitive people, general population controls with a high burden of complaints related to electromagnetic field (EMF) exposure in the literature (highest decile in complaint burden), and general population controls with a low burden of complaints (lowest decile in complaint burden). The major study endpoint was the ability of the subjects to differentiate between real magnetic stimulation and a sham condition. There were no significant differences between groups in the thresholds, neither of detecting the real magnetic stimulus nor in motor response. But the three groups differed significantly in differentiating between stimulation and sham condition, with the subjectively electrosensitive people having the lowest ability to differentiate and the control group with high level of EMF-related complaints having the best ability to differentiate. Differences between groups were mostly due to false alarm reactions in the sham condition reported by subjectively electrosensitives (SES). We found no objective correlate of the self perception of being "electrosensitive." Overall, our experiment does not support the hypothesis that subjectively electrosensitive patients suffer from a physiological hypersensitivity to EMFs or stimuli. Further research should focus on disposing factors explaining the unspecific sensory hyperresponsiveness of subjectively electrosensitive subjects.     

Cowhage-induced itch as an experimental model for pruritus. A comparative study with histamine-induced itch

Background

Histamine is the prototypical pruritogen used in experimental itch induction. However, in most chronic pruritic diseases, itch is not predominantly mediated by histamine. Cowhage-induced itch, on the other hand, seems more characteristic of itch occurring in chronic pruritic diseases.

Objectives

We tested the validity of cowhage as an itch-inducing agent by contrasting it with the classical itch inducer, histamine, in healthy subjects and atopic dermatitis (AD) patients. We also investigated whether there was a cumulative effect when both agents were combined.

Methods

Fifteen healthy individuals and fifteen AD patients were recruited. Experimental itch induction was performed in eczema-free areas on the volar aspects of the forearm, using different itch inducers: histamine, cowhage and their combination thereof. Itch intensity was assessed continuously for 5.5 minutes after stimulus application using a computer-assisted visual analogue scale (COVAS).

Results

In both healthy and AD subjects, the mean and peak intensity of itch were higher after the application of cowhage compared to histamine, and were higher after the combined application of cowhage and histamine, compared to histamine alone (p<0.0001 in all cases). Itch intensity ratings were not significantly different between healthy and AD subjects for the same itch inducer used; however AD subjects exhibited a prolonged itch response in comparison to healthy subjects ( p<0.001).

Conclusions

Cowhage induced a more intense itch sensation compared to histamine. Cowhage was the dominant factor in itch perception when both pathways were stimulated in the same time. Cowhage-induced itch is a suitable model for the study of itch in AD and other chronic pruritic diseases, and it can serve as a new model for testing antipruritic drugs in humans.     

Independent responses of Pacinian and Non-Pacinian systems with hand-transmitted vibration detected from masked thresholds

This study was designed to identify psychophysical channels responsible for the detection of hand-transmitted vibration. Perception thresholds for vibration (16, 31.5, 63 and 125?Hz sinusoidal for 600?ms) at the distal phalanx of the middle finger and the whole hand were determined with and without simultaneous masking stimuli (1/3 octave bandwidth Gaussian random vibration centered on either 16?Hz or 125?Hz for 3000?ms, varying in magnitude 0 to 30?dB above threshold). At all frequencies from 16 to 125?Hz, absolute thresholds for the hand were significantly lower than those for the finger. Changes in threshold as a function of masker level were used to estimate the thresholds of three psychophysical channels (i.e. P, NP I, and NP II channels). Increased vibrotactile sensitivity of the hand compared to the finger seems to be not entirely due to increased spatial summation via the Pacinian system (P channel); non-Pacinian system (NP I and NP II channels) also contributed to perception. Differing transmission of vibration between the hand and the finger may have also influenced the thresholds.     

Sex Differences in Itch Perception and Modulation by Distraction – an fMRI Pilot Study in Healthy Volunteers

Background

Even though itch is a common syndrome of many diseases there is only little knowledge about sex and gender differences in pruritus, especially in central itch perception and modulation. To our knowledge, this is the first fMRI study examining sex differences in perception and its modulation by distraction.

Methods

Experimental itch was induced by application of histamine (0.1 mM) via microdialysis fibers twice at the left forearm and twice at the left lower leg in 33 healthy volunteers (17 females, 16 males). The brain activation patterns were assessed by fMRI during itch without and with distraction (Stroop task). Between the various conditions, subjects were asked to rate itch intensity, desire to scratch and pain intensity. In a second experiment in 10 of the 33 volunteers histamine was replaced by saline solution to serve as control for the ‘Stroop’ condition.

Results

Women generally presented higher itch intensities compared to men during itch over the course of the experiment. A more specific analysis revealed higher itch intensities and desire to scratch in women during experimental induced itch that can be reduced by distraction at the lower legs when itch is followed by ‘Stroop’. In contrast, men depicted significant reduction of ‘itch’ by ‘Stroop’ at the forearms. Women depicted higher brain activation of structures responsible for integration of sensory, affective information and motor integration/planning during ‘itch’ and ‘Stroop’ condition when compared to men. No sex differences were seen in the saline control condition.

Conclusion

Women and men exhibited localisation dependent differences in their itch perception with women presenting higher itch intensities and desire to scratch. Our findings parallel clinical observations of women reporting higher itch intensities depending on itch localisation and suffering more from itch as compared to men.     

Tactile learning and the individual evaluation of the reward in honey bees (Apis mellifera L.)

Using the proboscis extension response we conditioned pollen and nectar foragers of the honey bee (Apis mellifera L.) to tactile patterns under laboratory conditions. Pollen foragers demonstrated better acquisition, extinction, and reversal learning than nectar foragers. We tested whether the known differences in response thresholds to sucrose between pollen and nectar foragers could explain the observed differences in learning and found that nectar foragers with low response thresholds performed better during acquisition and extinction than ones with higher thresholds. Conditioning pollen and nectar foragers with similar response thresholds did not yield differences in their learning performance. These results suggest that differences in the learning performance of pollen and nectar foragers are a consequence of differences in their perception of sucrose. Furthermore, we analysed the effect which the perception of sucrose reward has on associative learning. Nectar foragers with uniform low response thresholds were conditioned using varying concentrations of sucrose. We found significant positive correlations between the concentrations of the sucrose rewards and the performance during acquisition and extinction. The results are summarised in a model which describes the relationships between learning performance, response threshold to sucrose, concentration of sucrose and the number of rewards. Accepted: 14 April 1999     

Body Site Variation of Cool Perception Thresholds,with Observations on Paradoxical Heat

Thresholds for the perception of coolness and heat pain were determined in sessions that randomly intermixed temperature increases and decreases. Four body sites were tested bilaterally: thenar eminence of the hand, plantar surface of the foot, dorsolateral forearm, and lateral calf. Coolness thresholds were lowest for the hand, intermediate for the forearm, and highest for the leg and foot. Laterality differences were not statistically significant.

In 34% of the sessions, subjects did not consistently report cool or cold sensations with detectable temperatue decreases. When they did not report cool or cold, they most often reported heat or pain, thus exhibiting the phenomenon of “paradoxical heat”. There were significantly more paradoxical heat responses when cooling stimuli were intermixed with painfully hot stimuli than when they were intermixed with only warm stimuli.

There was no significant correlation observed between thresholds for coolness and heat pain, either across body sites or across subjects at any single body site. This result implies that the various factors relevant to thermal sensitivity (i.e., thermal properties of the epidermis, innervation density) are differentially important for cool versus heat pain perception.     

Sequence clustering threshold has little effect on the recovery of microbial community structure

Analysis of microbial community structure by multivariate ordination methods, using data obtained by high‐throughput sequencing of amplified markers (i.e., DNA metabarcoding), often requires clustering of DNA sequences into operational taxonomic units (OTUs). Parameters for the clustering procedure tend not to be justified but are set by tradition rather than being based on explicit knowledge. In this study, we explore the extent to which ordination results are affected by variation in parameter settings for the clustering procedure. Amplicon sequence data from nine microbial community studies, representing different sampling designs, spatial scales and ecosystems, were subjected to clustering into OTUs at seven different similarity thresholds (clustering thresholds) ranging from 87% to 99% sequence similarity. The 63 data sets thus obtained were subjected to parallel DCA and GNMDS ordinations. The resulting community structures were highly similar across all clustering thresholds. We explain this pattern by the existence of strong ecological structuring gradients and phylogenetically diverse sets of abundant OTUs that are highly stable across clustering thresholds. Removing low‐abundance, rare OTUs had negligible effects on community patterns. Our results indicate that microbial data sets with a clear gradient structure are highly robust to choice of sequence clustering threshold.     

Use of backward masking test for the study of visual information processing in healthy subjects and schizophrenic patients

The study of 14 healthy subjects and 15 schizophrenic patients was conducted under visual backward masking conditions. Sensory thresholds were identified using the method of constant stimuli. A special modification of the backward masking technique with lateralized presentation of test and masking stimuli was used to study the lateral characteristics of visual attention. It was found that the thresholds of letter stimulus identification were significantly higher in patients with schizophrenia than in healthy subjects. Only in patients the asymmetry of visual perception was revealed with the higher recognition thresholds in the left visual hemifield. The overall data analysis suggests an association between increased recognition thresholds in schizophrenic patients and changes in the interruption mechanism functioning at the neocortex level.     

Reductions in finger blood flow in men and women induced by 125-Hz vibration: association with vibration perception thresholds

Vibration of one hand reduces blood flow in the exposed hand and in the contralateral hand not exposed to vibration, but the mechanisms involved are not understood. This study investigated whether vibration-induced reductions in finger blood flow are associated with vibrotactile perception thresholds mediated by the Pacinian channel and considered sex differences in both vibration thresholds and vibration-induced changes in digital circulation. With force and vibration applied to the thenar eminence of the right hand, finger blood flow and finger skin temperature were measured in the middle fingers of both hands at 30-s intervals during seven successive 4-min periods: 1) pre-exposure with no force or vibration, 2) pre-exposure with force, 3) vibration 1, 4) rest with force, 5) vibration 2, 6) postexposure with force, and 7) recovery with no force or vibration. A 2-N force was applied during periods 2-6 and 125-Hz vibration at 0.5 and 1.5 ms(-2) root mean square (r.m.s.; unweighted) was applied during periods 3 and 5, respectively. Vibrotactile thresholds were measured at the thenar eminence of right hand using the same force, contact conditions, and vibration frequency. When the vibration magnitude was greater than individual vibration thresholds, changes in finger blood flow were correlated with thresholds (with both 0.5 and 1.5 ms(-2) r.m.s. vibration): subjects with lower thresholds showed greater reductions in finger blood flow. Women had lower vibrotactile thresholds and showed greater vibration-induced reductions in finger blood flow. It is concluded that mechanoreceptors responsible for mediating vibration perception are involved in the vascular response to vibration.     

Variety‐specific Epidemiology of Cercospora beticola Sacc. and Consequences for Threshold‐based Timing of Fungicide Application in Sugar Beet

In Central Europe, fungicides to control leaf spot disease in sugar beet caused by Cercospora beticola are applied based on thresholds of disease incidence (DI, per cent of infected plants). As variety‐specific fungicide application was not analyzed to date, the epidemiology of C. beticola and its effect on white sugar yield (WSY) in varieties with different susceptibility were investigated at seven sites in Germany and Austria in 2004 and 2005. All varieties reached the summary thresholds 5 / 15 / 45% DI in all environments. Fitting a logistic growth curve to DI revealed significant differences among varieties. At high disease pressure, susceptible varieties reached a considerably higher disease severity (DS, per cent of infected leaf area) at harvest and a larger area under disease progress curve (AUDPC) than resistant varieties. Fitting a logistic growth curve to DS showed an increasing differentiation among varieties with time. The growth rate estimated based on the logistic growth curve was the only variable that performed equally well in differentiating varieties under low and high disease pressure. With increasing disease pressure, varieties differed considerably in WSY, but differences between susceptible and resistant varieties were significant only in some environments. The disease‐loss relation between AUDPC and relative WSY was variety‐specific. Resistant varieties had an approximately identical WSY with and without infection and compensated for negative infection effects even at higher AUDPC. Therefore, at high disease pressure, resistant varieties had a higher relative yield compared to susceptible ones. However, our results indicate that there is no need to develop variety‐specific thresholds, but resistant varieties reach the established thresholds later than susceptible ones. Consequently, the time of fungicide application can be delayed in resistant varieties. This will help to reduce the use of fungicides to the bare essentials as requested for the integrated crop protection management.     

Age-related differences in cutaneous warm sensation thresholds of human males in thermoneutral and cool environments

The purpose of this study was to investigate age-related differences in cutaneous temperature thresholds for warm thermal sensitivity in a thermoneutral (28 °C) and in a cool environment (22 °C). Peripheral warm thresholds were measured on nine body regions (cheek, chest, abdomen, upper arm, forearm, hand, thigh, shin, and foot) using a thermal stimulator in 12 young (22±1 years) and 13 elderly male subjects (67±3 years). The results showed that: (1) mean skin temperature did not differ by age in both environments; (2) the cutaneous warm thresholds for the hand, shin, and foot were significantly higher for the elderly than for the young in both environments (p<0.01), whereas the remaining body parts showed no age difference; (3) the most insensitive region for elderly males was the shin for both environments (p<0.01), while for young there was no statistical significant difference with T_a 28 °C; (4) the shin of the elderly was seven and nine times less sensitive to warmth when compared to those of the cheek at T_a 28 and 22 °C, respectively; and (5) warm thresholds were 3-4 °C greater at T_a 22 °C than at 28 °C, only for the elderly males' shin and foot (p<0.05), while for young the difference between T_a 22 and 28 °C was not statistically significant. The results indicate that age-related differences in cutaneous warm perception appear to be non-uniform over the body and significant on extremities; there is a greater bluntness of warm sensitivity in the cool environment for elderly males.     

Sympathetic skin responses recorded from non-palmar and non-plantar skin sites: their role in the evaluation of thermal sweating

Objective: To characterize the sympathetic skin responses (SSRs) recorded from non-palmar and non-plantar (non-Pa/Pl) skin sites and to evaluate their clinical usefulness.Methods: SSRs were recorded from 6 non-Pa/Pl sites as well as palmar and plantar (Pa/Pl) sites using magnetic neck stimulation in 33 normal subjects, 17 neurological patients with dysautonomia and one patient with lumbar sympathectomy. A conventional thermoregulatory sweat test (TST) was also carried out in 3 patients.Results: Clear and reproducible SSRs were obtained from all recording sites in all of the normal subjects when the skin temperatures of the subjects were maintained above 34°C and the subjects drank 100–200 ml of hot water. The distribution of absent SSRs was closely correlated with that of anhidrosis or a sweating delay shown by the TST in the patients. Nine of the 17 neurological patients (53%) showed normal responses at Pa/Pl sites, and abnormal responses at non-Pa/Pl sites.Conclusions: Recording SSRs from multiple skin sites including non-Pa/Pl sites after magnetic stimulation is more sensitive in detecting sudomotor dysfunction than is the conventional method of recording SSRs from only Pa/Pl sites. In addition, this new method is very useful for the objective clinical evaluation of thermal sweating.     

Diversity of topological palmar patterns in Iranian populations

The bilateral palmar prints of 3,158 females and males from 13 Iranian populations of diverse origins were analyzed to see how well topological palmar pattern frequencies reflect population distances. The results showed bimanual variation among most of the populations studied. Sex variation showed significant differences among all of the populations studied. Distance analysis and constructed dendrograms showed separation between the populations studied. These distances were frequently in agreement with the known ethnohistoric background of the populations studied. The male data gave better results. It appears that topological palmar patterns are a better indicator of population distance than topological finger patterns.     

NEWER METHODS FOR SELECTION OF PATIENTS FOR LUMBAR SYMPATHECTOMY

The degree of vasodilatation achieved by various diagnostic methods (arterial occlusion, ganglionic block established by certain agents, lumbar sympathetic block, spinal anesthesia, and indirect heating) was studied by means of the pneumo-plethysmogram as well as through readings of skin temperature and skin resistance. The data obtained were interpreted as to their value in determining the type of patient with vascular disease for whom lumbar sympathectomy would be of noticeable benefit. Arterial occlusion proved itself a rapid and simple method which in most patients produced satisfactory results. As a rule, lumbar sympathectomy was effective in patients who preoperatively had shown a positive response upon release of arterial occlusion. A negative response, that is, absence of significant increase in blood flow, does not necessarily indicate organic disease, and cannot be taken to mean that lumbar sympathectomy would always be ineffective. Ganglionic block, using 2.6 dimethyl piperidinium bromide or tetraethylammonium ion, was generally less reliable in indicating the probable results of sympathectomy than lumbar sympathetic block or indirect heating. Lumbar sympathetic block with procaine was followed by a greater increase in skin temperature and blood flow than spinal anesthesia, and permitted far more accurate conclusions as to the probable outcome of sympathectomy. Subsequent to indirect heating the plethysmogram showed characteristic differences depending on the degree of vascular disease present. From the effect of this simple, safe and painless method upon the relative blood flow to the toe it becomes possible to arrive at a comparatively accurate estimate of the clinical benefit to be expected from lumbar sympathectomy.     

Pain perception in competitive swimmers.

The pain perception of 30 competitive swimmers was studied using experimentally induced ischaemic pain. The pain thresholds and tolerances of this group were compared with those of 30 club swimmers and 26 non-competitive athletes. While pain thresholds showed little difference between the groups, pain tolerances were considerably different. Pain tolerances of the competitive swimmers varied according to the stage of the training season. The relation between ischaemic pain and that experienced during swimming training was studied using a pain questionnaire composed of several systematically structured verbal categories. Both types of pain were classified along similar dimensions, and it was concluded that the experimentally demonstrated pain tolerances could be generalized to the normal pain perception of the subjects. The origins of the enhanced pain tolerances of the competitive swimmers would seem to lie in their systematic exposure to brief periods of intense pain. These data could have relevance for the treatment of chronic pain in certain diseases.     

A reverse ulnar hypothenar flap for finger reconstruction

A reverse-flow island flap from the hypothenar eminence of the hand was applied in 11 patients to treat palmar skin defects, amputation injuries, or flexion contractures of the little finger. There were three female and eight male patients, and their ages at the time of surgery averaged 46 years. A 3 x 1.5 to 5 X 2 cm fasciocutaneous flap from the ulnar aspect of the hypothenar eminence, which was located over the abductor digiti minimi muscle, was designed and transferred in a retrograde fashion to cover the skin and soft-tissue defects of the little finger. The flap was based on the ulnar palmar digital artery of the little finger and in three patients was sensated by the dorsal branch of the ulnar nerve or by branches of the ulnar palmar digital nerve of the little finger. Follow-up periods averaged 42 months. The postoperative course was uneventful for all patients, and all of the flaps survived without complications. The donor site was closed primarily in all cases, and no patient complained of significant donor-site problems. Satisfactory sensory reinnervation was achieved in patients who underwent sensory flap transfer, as indicated by 5 mm of moving two-point discrimination. A reverse island flap from the hypothenar eminence is easily elevated, contains durable fasciocutaneous structures, and has a good color and texture match to the finger pulp. This flap is a good alternative for reconstruction of palmar skin and soft-tissue defects of the little finger.     

Vibrotactile Perception in Finger Pulps and in the Sole of the Foot in Healthy Subjects among Children or Adolescents

Aims

To evaluate vibrotactile perception at different frequencies in fingers and in foot in healthy girls and boys.

Methods

Vibration perception thresholds (VPTs) were measured in 283 healthy (8–20 years), consecutively included, girls (n=146) and boys (n=137); i.e., 269 children after excluding those with diseases or disorders possibly affecting the nervous system. Thresholds were measured in finger pulps of index and little fingers (seven frequencies; 8–500 Hz) and at first and fifth metatarsal head and at heel in the sole of the foot (six frequencies; 8–250 Hz;) using Multi Frequency Tactilometry.

Results

VPTs, divided in six groups by age and gender (i.e., 8–10 years, 11–15 years and 16–20 years), at all three sites in the sole increased with higher frequencies, but without gender differences. Thresholds at 64 and 125 Hz were generally higher at heel compared to metatarsal heads. VPTs in finger pulps of index and little fingers, with no finger differences, had a different pattern with increasing thresholds with frequency, but with lower thresholds at 64 and 125 Hz. Thresholds at lower frequencies were higher in finger pulps, while at higher frequencies VPTs were lower in finger pulps than in the sole of the foot; thus, vibration perception in the sole was better than perception in finger pulps at lower frequencies and opposite at higher frequencies. VPTs were higher among adolescents than in younger children in the foot, while thresholds were lower in the finger pulps among adolescents, particularly in index finger. Thresholds in finger pulps of index and little fingers, particularly at higher frequencies, correlated with each other, which the three sites in the sole also did.

Conclusions

VPTs in fingers and in feet are different as related to frequency in healthy girls and boys. Multi Frequency Tactilometry is a future valuable method to detect neuropathy in children and adolescents.     

Tolerance responses to herbivory: implications for future management strategies in potato

Tolerance is a plant response to herbivory that allows plants to sustain defoliation without any fitness consequences. In agriculture, the maximum amount of defoliation that crops can experience without yield loss is defined as the damage threshold. Damage thresholds can be used to develop tolerance‐based management strategies, which would offer guidelines for farmers for when pest control should be enacted to minimise pesticide use while maintaining yield. Damage thresholds for many varieties of potatoes, Solanum tuberosum, have been documented, but not consolidated into a general framework. We aggregated data from published studies and quantified the effects of variety, maturity group, life stage and defoliation mechanisms on damage thresholds to inform a tolerance‐based management strategy for potato. Late maturing varieties did not have different damage thresholds than early maturing varieties. Damage thresholds were greater than 60% defoliation at emergence and post‐bloom and less than 40% defoliation pre‐bloom and during bloom. If the stems were damaged, emergence and post‐bloom damage thresholds were reduced from 60% defoliation without stem damage to 35% and 52% defoliation with stem damage. Likewise, the damage thresholds during bloom were reduced to 20% defoliation when stems were damaged. We propose using action thresholds based on defoliation as a baseline to develop a tolerance‐based management strategy for potatoes.