***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: & NA ; The purpose of the present study was to determine whether gender differences exist in the forebrain cerebral activation patterns of the brain during pain perception . Accordingly , positron emission tomography ( PET ) with intravenous injection of H2 15O was used to detect increases in regional cerebral blood flow ( rCBF ) in normal right‐h and ed male and female subjects as they discriminated differences in the intensity of innocuous and noxious heat stimuli applied to the left forearm . Each subject was instructed in magnitude estimation based on a scale for which 0 indicated ‘ no heat sensation ’ ; 7 , ‘ just barely painful ’ and 10 , ‘ just barely tolerable ’ . Thermal stimuli were 40 ° C or 50 ° C heat , applied with a thermode as repetitive 5‐s contacts to the volar forearm . Both male and female subjects rated the 40 ° C stimuli as warm but not painful and the 50 ° C stimuli as painful but females rated the 50 ° C stimuli as significantly more intense than did the males ( P=0.0052 ) . Both genders showed a bilateral activation of premotor cortex in addition to the activation of a number of contralateral structures , including the posterior insula , anterior cingulate cortex and the cerebellar vermis , during heat pain . However , females had significantly greater activation of the contralateral prefrontal cortex when compared to the males by direct image subtraction . Volume of interest comparison ( t‐statistic ) also suggested greater activation of the contralateral insula and thalamus in the females ( P<0.05 ) . These pain‐related differences in brain activation may be attributed to gender , perceived pain intensity , or to both factors OBJECTIVE To determine the prevalence and characteristics of fibromyalgia in the general population . METHODS A r and om sample of 3,006 persons in Wichita , KS , were characterized according to the presence of no pain , non-widespread pain , and widespread pain . A sub sample of 391 persons , including 193 with widespread pain , were examined and interviewed in detail . RESULTS The prevalence of fibromyalgia was 2.0 % ( 95 % confidence interval [ 95 % CI ] 1.4 , 2.7 ) for both sexes , 3.4 % ( 95 % CI 2.3 , 4.6 ) for women , and 0.5 % ( 95 % CI 0.0 , 1.0 ) for men . The prevalence of the syndrome increased with age , with highest values attained between 60 and 79 years ( > 7.0 % in women ) . Demographic , psychological , dolorimetry , and symptom factors were associated with fibromyalgia . CONCLUSION Fibromyalgia is common in the population , and occurs often in older persons . Characteristic features of fibromyalgia -- pain threshold and symptoms -- are similar in community and clinic population s , but overall severity , pain , and functional disability are more severe in the clinic population UNLABELLED Pain catastrophizing is among the most robust predictors of pain outcomes , and a disruption in endogenous pain-inhibitory systems is 1 potential mechanism that may account for increased pain among individuals who report higher pain catastrophizing . Pain catastrophizing may negatively influence diffuse noxious inhibitory controls ( DNIC ) , a measure of endogenous pain inhibition , through complex anatomical circuitry linking cortical responses to pain with processes that modulate pain . The current study examined whether DNIC mediated the relationship between catastrophizing and pain among 35 healthy young adults and examined the moderating effects of sex to determine whether the magnitude or direction of associations differed among men and women .  DNIC was assessed using pressure pain thresholds on the forearm before and during a cold pressor task . Using bias-corrected bootstrapped confidence intervals , results showed that diminished DNIC was a significant partial mediator of the relation between greater pain-related catastrophizing and more severe pain ratings . Participant sex moderated these associations ; higher catastrophizing predicted lower DNIC for men and women , however , the effect of catastrophizing on pain ratings was partially mediated by DNIC for women only . These findings further support the primary role of pain catastrophizing in modulation of pain outcomes . PERSPECTIVE These findings support the hypothesis that the heightened pain reported by individuals higher in pain catastrophizing may be related to a disruption in the endogenous modulation of pain , operationalized by assessing DNIC . Whether interventions that reduce pain catastrophizing affect pain outcomes via effects on DNIC is in need of investigation In this study we tested the hypothesis that hypoalgesia in individuals at risk for hypertension is related to enhanced activation of supraspinal pain modulation systems . Supraspinal inhibition of pain signals was assessed using a diffuse noxious inhibitory control paradigm , in which a noxious conditioning stimulus was used to suppress pain in response to a noxious test stimulus applied to a remote area of the body . Specifically , the nociceptive flexion reflex ( NFR ) was assessed in 113 healthy young adults before , during , and after exposure to forearm tourniquet ischemia .  Consistent with previous evidence of hypoalgesia in individuals at risk for hypertension , offspring of hypertensive individuals exhibited significantly higher NFR thresholds than offspring of normotensive persons . Although NFR activity was significantly decreased in all participants during concomitant application of forearm ischemia , the degree of attenuation of NFR activity was not significantly different as a function of risk for hypertension We present the first prevalence study of specific headache entities using the operational diagnostic criteria of the International Headache Society . One thous and 25 - 64 year old men and women , who lived in the western part of Copenhagen County were r and omly drawn from the Danish National Central Person Registry . All subjects were invited to a general health examination focusing on headache and including : a self-administered question naire concerning sociodemographic variables , a structured headache interview and a general physical and neurological examination . The participation rate was 76 % . Information about 79 % of the non- participants showed a slightly differing headache prevalence which was not quantitatively important . The following results in participants are therefore representative of the total sample . The lifetime prevalences of headache ( including anybody with any form of headache ) , migraine , and tension-type headache were 93 , 8 and 69 % in men ; and 99 , 25 and 88 % in women . The point prevalence of headache was 11 % in men and 22 % in women . Prevalence of migraine in the previous year was 6 % in men and 15 % in women and the corresponding prevalences of tension-type headache were 63 and 86 % . Differences according to sex were significant with a male : female ratio of 1:3 in migraine , and 4:5 in tension-type headache . The prevalence of tension-type headache decreased with increasing age , whereas migraine showed no correlation to age within the studied age interval . Headache disorders are extremely prevalent and represent a major health problem , which merits increased attention Objective Sex differences in pain sensitivity and stress reactivity have been well documented . Little is known about the role of the endogenous opioid system in these differences . This study was conducted to compare adrenocortical , pain sensitivity , and blood pressure responses to opioid blockade using naltrexone in men and women . Methods Twenty-six participants completed 2 sessions during which placebo or 50 mg of naltrexone was administered , using a double-blind , counterbalanced design . Thermal pain threshold and heat tolerance were assessed . Participants also rated pain during a 90-second cold pressor test ( CPT ) and completed the McGill Pain Question naire ( MPQ ) after each pain challenge .  Blood and saliva sample s and cardiovascular and mood measures were obtained throughout the sessions . Results Plasma cortisol , adrenocorticotropin , beta endorphin , prolactin , and salivary cortisol levels increased similarly in men and women after naltrexone administration compared with placebo . Women reported more pain during both pain procedures and had lower thermal pain tolerance . In response to naltrexone , women exhibited reduced blood pressure responses and reduced MPQ pain ratings after CPT . No effects of naltrexone on these measures were found in men . Conclusions Although men and women exhibited similar hormonal responses to opioid receptor blockade , women reported less pain and showed smaller blood pressure responses during CPT . Results suggest differential effects of the endogenous opioid system on pain perception and blood pressure in men and women OBJECTIVE To examine possible deficiencies in endogenous pain modulating mechanisms in fibromyalgia patients compared with matched pain-free control subjects . DESIGN /SUBJECTS/ METHODOLOGY : Pain reduction was investigated in 25 female patients with fibromyalgia and 26 age-matched healthy women using the diffuse noxious inhibitory controls ( DNIC ) paradigm . Tonic thermal stimuli at painful and nonpainful intensities , tailored to individual heat pain thresholds , were employed to induce pain inhibition . The anticipated effect was assessed by measuring the electrical pain threshold and detection threshold , using a double staircase method . Only nontender control points were stimulated ( thermode on the foot , electrodes on the inner forearm ) . RESULTS The patients with fibromyalgia had significantly lower heat pain thresholds than the healthy subjects , but similar electrical detection and pain thresholds . The repeatedly applied electrical stimuli result ed in a degree of perceptual adaptation that was similar between the two groups . However , concurrent tonic thermal stimuli , at both painful and nonpainful levels , significantly increased the electrical pain threshold in the healthy subjects but not in the fibromyalgia patients . The electrical detection threshold was not affected in either group . CONCLUSIONS Pain modulation , produced by a concurrent tonic stimulus in healthy persons , was not seen in the fibromyalgia group . The patients either had deficient pain modulation or were unable to tolerate a tonic stimulus intense enough to engage a modulatory process . It remains to be established whether the pain reduction found in the healthy subjects was the conventional DNIC effect , another effect ( e.g. , distraction ) , or a combination of both & NA ; The aim of this study was to investigate the effects of diffuse noxious inhibitory controls ( DNICs ) on the temporal summation of the nociceptive flexion reflex ( RIII reflex ) in humans . Recordings were obtained from 36 healthy adults ( 16 M , 20 F ) , and the area and temporal summation threshold ( TST ) of the RIII reflex were measured . The subjective intensity of the painful sensation was rated on an 11‐point visual analogue scale ( VAS ) . Neurophysiological and VAS measurements were recorded after activation of DNICs by means of the cold pressor test ( CPT ) , which involved immersing the h and in cold water ( 2–4 ° C ) . A slight significant lower TST was found in the females versus the males . In all the subjects , the CPT induced a significant TST increase and RIII area reduction compared with the control session . The VAS results paralleled those of the RIII reflex area and TST . During the CPT , a significant difference in the percentage TST increase emerged between females and males , being lower in the former . Similarly , we found a significantly lower percentage reduction of the RIII area in women than in men during the CPT . To summarize , activation of DNICs through the CPT significantly increased the TST of the RIII reflex in healthy subjects . This inhibitory effect was gender‐specific . Whereas other findings are based on psychophysical evaluations , the results of this experimental study provide an objective neurophysiological demonstration that DNICs attenuate temporal summation in humans and confirm the presence of significant differences in pain modulation mechanisms between men and women & NA ; Little is known about sex differences in the temporal pattern of descending inhibitory mechanisms , such as descending noxious inhibitory control ( DNIC ) . Sex differences in temporal characteristics of DNIC were investigated by measuring pressure pain thresholds ( PPTs ) over time in the trapezius muscles ( local pain areas ) and the posterolateral neck muscles ( referred pain areas ) following repeated bilateral injection of hypertonic versus isotonic saline into both trapezius muscles . Ten females and 11 males received two consecutive bilateral injections , with 15 min interval , of either 5.8 % hypertonic saline ( 0.5 ml in each side for each bilateral injection ) or isotonic saline as a control in a r and omized manner . Following hypertonic saline injection , the maximal pain intensities of the first and second bilateral injections were significantly higher in females than in males . The PPTs in the trapezius muscles were significantly lower in females than in males . Significantly higher PPTs ( hypoalgesia ) in men than in women were shown 15 min after the first bilateral injection , and 7.5 and 15 min after the second bilateral injection in the referred pain areas . Importantly , the second bilateral injection failed to further increase the PPTs for both sexes . These results showed that there were sex differences in temporal characteristics of descending inhibition with long‐lasting hypoalgesia in men than in women . Repeated noxious muscular stimuli may inhibit further build‐up of DNIC , which may reflect a mechanism of plasticity of the descending inhibitory systems following recurrent nociceptive barrage for both sexes & NA ; The aims of this study were to investigate possible sex differences in ( a ) intraoral pain evoked by topical application of capsaicin to the gingiva , and ( b ) the modulation of this pain by diffuse noxious inhibitory controls ( DNIC ) . Three groups with a total of fifty‐four healthy volunteers ( 20 men , 20 women using oral contraceptives ( W+OC ) , 14 women not using ( W−OC ) ) completed the study . In two sessions , intraoral pain was evoked by topical application of 30 μL 5 % capsaicin to the gingiva . Conditioning stimuli were applied with three min h and immersion in ice water in one session and 30 ° C 
    Output:
    
Studies evaluating pain thresholds and nociceptive flexion reflex indicated the opposite when simply averaged across studies ; however , weighted analyses of threshold found more efficient DNIC in males .
Gender differences in DNIC effect depend on both the experimental methodology and the modes of measurement of the effect