Anticipatory prefrontal cortex activity underlies stress-induced changes in Pavlovian fear conditioning.

Excessive stress exposure often leads to emotional dysfunction, characterized by disruptions in healthy emotional learning, expression, and regulation processes. A prefrontal cortex (PFC)-amygdala circuit appears to underlie these important emotional processes. However, limited human neuroimaging research has investigated whether these brain regions underlie the altered emotional function that develops with stress. Therefore, the present study used functional magnetic resonance imaging (fMRI) to investigate stress-induced changes in PFC-amygdala function during Pavlovian fear conditioning. Participants completed a variant of the Montreal Imaging Stress Task (MIST) followed (25 min later) by a Pavlovian fear conditioning task during fMRI. Self-reported stress to the MIST was used to identify three stress-reactivity groups (Low, Medium, and High). Psychophysiological, behavioral, and fMRI signal responses were compared between the three stress-reactivity groups during fear conditioning. Fear learning, indexed via participant expectation of the unconditioned stimulus during conditioning, increased with stress reactivity. Further, the High stress-reactivity group demonstrated greater autonomic arousal (i.e., skin conductance response, SCR) to both conditioned and unconditioned stimuli compared to the Low and Medium stress-reactivity groups. Finally, the High stress group did not regulate the emotional response to threat. More specifically, the High stress-reactivity group did not show a negative relationship between conditioned and unconditioned SCRs. Stress-induced changes in these emotional processes paralleled changes in dorsolateral, dorsomedial, and ventromedial PFC function. These findings demonstrate that acute stress facilitates fear learning, enhances autonomic arousal, and impairs emotion regulation, and suggests these stress-induced changes in emotional function are mediated by the PFC.

Depressive Symptoms and Sleep Efficiency Sequentially Mediate Racial Differences in Temporal Summation of Mechanical Pain.

BACKGROUND: Racial differences in endogenous pain facilitatory processes have been previously reported. Evidence suggests that psychological and behavioral factors, including depressive symptoms and sleep, can alter endogenous pain facilitatory processes. Whether depressive symptoms and sleep might help explain racial differences in endogenous pain facilitatory processes has yet to be determined. PURPOSE: This observational, microlongitudinal study examined whether depressive symptoms and sleep were sequential mediators of racial differences in endogenous pain facilitatory processes. METHODS: A total of 50 (26 African American and 24 non-Hispanic white) community-dwelling adults without chronic pain (mean 49.04 years; range 21-77) completed the Center for Epidemiological Studies Depression Scale prior to seven consecutive nights of sleep monitoring with actigraphy in the home environment. Participants subsequently returned to the laboratory for assessment of endogenous pain facilitation using a mechanical temporal summation protocol. RESULTS: Findings revealed greater depressive symptoms, poorer sleep efficiency, and greater temporal summation of mechanical pain in African Americans compared to non-Hispanic whites. In a sequential mediation model, greater depressive symptoms predicted poorer sleep efficiency (t = -2.55, p = .014), and poorer sleep efficiency predicted enhanced temporal summation of mechanical pain (t = -4.11, p < .001), particularly for African Americans. CONCLUSIONS: This study underscores the importance of examining the contribution of psychological and behavioral factors when addressing racial differences in pain processing. Additionally, it lends support for the deleterious impact of depressive symptoms on sleep efficiency, suggesting that both sequentially mediate racial differences in endogenous pain facilitation.

Minority Aging and Endogenous Pain Facilitatory Processes.

OBJECTIVE: The aim of the current study was to examine the relationships among age, ethnicity, and endogenous pain facilitation using temporal summation (TS) responses to mechanical and heat stimuli. DESIGN: The present study assessed hyperalgesia and pain facilitation to thermal and mechanical stimuli at the knee and distal sites in 98 pain-free men and women. Participants were drawn from two ethnic groups [African-American (AA) and non-Hispanic white (NHW)] and two age groups (19-35 and 45-85). RESULTS: Significant main effects of ethnicity were demonstrated for both mechanical and heat modalities (all P's ≤ 0.05), suggesting that AA participants, relative to NHW counterparts, demonstrated enhanced hyperalgesia. Age differences (older > younger) in hyperalgesia were found in mechanical pain ratings only. Results indicated that mechanical pain ratings significantly increased from first to maximal pain as a function of both age group and ethnicity (all P's ≤ 0.05), and a significant ethnicity by age interaction for TS of mechanical pain was found at the forearm (P < 0.05) and trended toward significance at the knee (P = 0.071). Post-hoc tests suggested that results were primarily driven by the older AA participants, who demonstrated the greatest mechanical TS. Additionally, evidence of differences in heat TS due to both ethnicity alone (all P's ≤ 0.05) and minority aging was also found. CONCLUSIONS: This study provides evidence suggesting that older AAs demonstrate enhanced pain facilitatory processes, which is important because this group may be at increased risk for development of chronic pain. These results underscore the necessity of testing pain modulatory mechanisms when addressing questions related to pain perception and minority aging.

An Examination of Pain Catastrophizing and Endogenous Pain Modulatory Processes in Adults with Chronic Low Back Pain.

OBJECTIVE: Research on chronic low back pain (cLBP) has focused heavily on structural abnormalities with emphasis on diagnostic imaging. However, for many cLBP patients, clinical pain and disability are not clearly associated with identifiable pathology of the spine or associated tissues. Therefore, alternative determinants such as psychological factors and dysfunctional pain modulatory processes have been suggested to be important. METHODS: This observational study examined differences in pain catastrophizing and endogenous pain modulation between 25 cLBP patients and 25 pain-free controls. Associations among pain catastrophizing, endogenous pain modulatory processes, clinical pain reports, and disability were also examined in cLBP patients. Endogenous pain modulation was examined using temporal summation (TS) of mechanical and heat pain stimuli as well as conditioned pain modulation (CPM) with algometry (test stimulus) and the cold pressor task (conditioning stimulus). RESULTS: Findings demonstrated significantly greater pain catastrophizing as well as greater TS of mechanical and heat pain for cLBP patients compared with controls. CPM was not present in cLBP patients or controls. Among cLBP patients, pain catastrophizing was significantly associated with disability, while TS of mechanical pain was significantly associated with clinical pain severity and disability. CONCLUSIONS: This study suggests that endogenous pain modulatory processes are altered for cLBP patients, particularly TS of mechanical and heat stimuli. Pain catastrophizing and TS of mechanical pain may have important clinical relevance for cLBP, given associations with clinical pain and disability; however, future research is needed to replicate these findings.

Amygdala and prefrontal cortex activity varies with individual differences in the emotional response to psychosocial stress.

Stress elicits a variety of psychophysiological responses that show large interindividual variability. Determining the neural mechanisms that mediate individual differences in the emotional response to stress would provide new insight that would have important implications for understanding stress-related disorders. Therefore, the present study examined individual differences in the relationship between brain activity and the emotional response to stress. In the largest stress study to date, 239 participants completed the Montreal Imaging Stress Task (MIST) while heart rate, skin conductance response (SCR), cortisol, self-reported stress, and blood oxygen level dependent (BOLD) functional MRI (fMRI) signal responses were measured. The relationship between differential responses (heart rate, SCR, cortisol, and self-reported stress) and differential BOLD fMRI data was analyzed. Dorsolateral prefrontal cortex (PFC), dorsomedial PFC, ventromedial PFC, and amygdala activity varied with the behavioral response (i.e., SCR and self-reported stress). These results suggest the PFC and amygdala support processes that are important for the expression and regulation of the emotional response to stress, and that stress-related PFC and amygdala activity underlie interindividual variability in peripheral physiologic measures of the stress response. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

At the Intersection of Ethnicity/Race and Poverty: Knee Pain and Physical Function.

BACKGROUND: Knee osteoarthritis (OA) disproportionately affects racial and ethnic minorities. Non-Hispanic Blacks (NHB) report a higher prevalence and severity of knee OA symptoms than their non-Hispanic White (NHW) counterparts. The role of poverty in explaining this disparity remains unclear. OBJECTIVE: The overall aim of this cross-sectional study was to determine whether ethnic/racial differences in knee pain and physical function varied according to poverty status. DESIGN: NHB and NHW adults with or at risk of knee OA self-reported sociodemographic information, and completed the Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC) and the Short Physical Performance Battery (SPPB). Annual income was adjusted for number of household occupants to determine poverty status (i.e., living above versus below poverty line). RESULTS: Findings revealed 120 individuals living above the poverty line (49% NHB, 77% NHW) and 71 individuals living below the poverty line (51% NHB, 23% NHW). Adjusted multivariable models revealed significant ethnic/race by poverty status interactions for knee pain (p = 0.036) and physical function (p = 0.032) on the WOMAC, as well as physical function on the SPPB (p = 0.042). Post hoc contrasts generally revealed that NHW adults living above the poverty line experienced the least severe knee pain and best physical function, while NHB adults living below the poverty line experienced the most severe knee pain and poorest physical function. CONCLUSIONS: Results of the present study add to the literature by emphasizing the importance of considering poverty and/or other indicators of socioeconomic status in studies examining ethnic/racial disparities in pain and physical function.

Anticipatory stress associated with functional magnetic resonance imaging: Implications for psychosocial stress research.

Stress tasks performed during functional magnetic resonance imaging (fMRI) elicit a relatively small cortisol response compared to stress tasks completed in a traditional behavioral laboratory, which may be due to apprehension of fMRI that elicits an anticipatory stress response. The present study investigated whether anticipatory stress is greater prior to research completed in an MRI environment than in a traditional behavioral laboratory. Anticipatory stress (indexed by cortisol) was greater prior to testing in the MRI environment than traditional behavioral laboratory. Furthermore, anticipation of fMRI elicited a cortisol response commensurate with the response to the stress task in the behavioral laboratory. However, in the MRI environment, post-stress cortisol was significantly lower than baseline cortisol. Taken together, these findings suggest the stress elicited by anticipation of fMRI may lead to acute elevations in cortisol prior to scanning, which may in turn disrupt the cortisol response to stress tasks performed during scanning.