Age-Related Changes in Pain Perception Are Associated With Altered Functional Connectivity During Resting State

Advancing our understanding of neuropathic pain in diabetes mellitus using conditioned pain modulation: further considerations for age and testing site

ABSTRACT

Neuropathy is common among individuals with diabetes mellitus, and is associated with decreased quality of life, greater comorbidity, and substantial economic burden. However, the mechanisms underlying painful diabetic polyneuropathy has yet to be fully elucidated. While it is recognized that diabetic polyneuropathy places patients at a greater risk for developing neuropathic pain, it is still not clear why some individuals develop pain and others do not. Similar to other chronic pain conditions, painful diabetic neuropathy is likely driven by alterations in both the peripheral and central nervous system. Experimental conditioned pain modulation paradigms have contributed substantially to our current understanding of chronic pain across various disease states. In a new study, researchers have extended this work by examining the efficiency of conditioned pain modulation in patients with painful and non-painful diabetic polyneuropathy. Surprisingly, the results indicate individuals with painful neuropathy experience greater endogenous pain inhibition, which may seem counterintuitive at first blush. Here, we discuss potential explanations and directions for future research, including consideration for age effects, testing site, and disease type, with the goal of further advancing this important line of research.

Anterior Cingulate Cortex Activity During Rest Is Related to Alterations in Pain Perception in Aging

Alterations in the affective component of pain perception are related to the development of chronic pain and may contribute to the increased vulnerability to pain observed in aging. The present study analyzed age-related changes in resting-state brain activity and their possible relation to an increased pain perception in older adults. For this purpose, we compared EEG current source density and fMRI functional-connectivity at rest in older (n = 20, 66.21 ± 3.08 years) and younger adults (n = 21, 20.71 ± 2.30 years) and correlated those brain activity parameters with pain intensity and unpleasantness ratings elicited by painful stimulation. We found an age-related increase in beta2 and beta3 activity in temporal, frontal, and limbic areas, and a decrease in alpha activity in frontal areas. Moreover, older participants displayed increased functional connectivity in the anterior cingulate cortex (ACC) and the insula with precentral and postcentral gyrus. Finally, ACC beta3 activity was positively correlated with pain intensity and unpleasantness ratings in older, and ACC-precentral/postcentral gyrus connectivity was positively correlated with unpleasantness ratings in older and younger participants. These results reveal that ACC resting-state hyperactivity is a stable trait of brain aging and may underlie their characteristic altered pain perception.

Intact pain modulation through manipulation of controllability and expectations in aging

BACKGROUND

Pain expectation and controllability can modulate pain processing. However, little is known about age-related effects on these cognitive factors involved in pain control. This study assessed age-related brain changes associated with pain expectation and controllability.

METHODS

17 healthy older adults (9 men; 65.65 ± 4.34 years) and 18 healthy younger adults (8 men; 20.56 ± 5.56 years) participated in the study. Pain evoked potentials and pain ratings were recorded while participants received painful electrical stimuli under two different conditions of pain controllability over the intensity of the stimulation (self-controlled vs. computer controlled) and two conditions of pain expectations (high vs. low pain).

RESULTS

Although the intensity of the painful stimulation was kept constant, all participants showed reduced pain perception in the controllable and low pain expectancy conditions. However, older participants showed reduced amplitudes of pain evoked potentials in the time window between 150 and 500 ms after stimulus onset as compared to younger participants. Moreover, younger participants showed greater negative amplitudes from 80 to 150 ms after stimulus onset for uncontrollable versus controllable pain.

CONCLUSIONS

These results suggest that although cognitive pain modulation is preserved during ageing, neural processing of pain is reduced in older adults.

SIGNIFICANCE

This research describes the impact of age on cognitive pain modulation evoked by the manipulation of pain controllability and pain expectations. Our findings constitute a first step in the understanding of the greater vulnerability of older individuals to chronic pain. Moreover, we show that older adults can benefit from cognitive pain control mechanisms to increase the efficacy of pain treatments.

[Physical exercise impact on variables related to emotional and functional well-being in older adults]

BACKGROUND AND AIM

The benefits of the physical exercise in aging, and specially in frailty, have been associated with reduced risk of mortality, chronic disease, and cognitive and functional impairments. Multi-component training, which combines strength, endurance, balance, and gait training, represents the most beneficial kind of physical exercise in older adults.

METHODS

Given the effectiveness of the multi-component training, a physical exercise program «Actívate» (based on the methodology Vivifrail), with the focus on «active aging», was conducted in the present study. Forty-nine older adults over 60 years participated in this program.

RESULTS

The physical exercise intervention led to a reduction in diastolic blood pressure, pain threshold and sleep disturbances (e. g. hypersomnia) (t ≥ 2.72, p < 0.01), as well as an increase of walking speed (t = 7.84, p ≤ 0.001). Further, quality of life factors (GENCAT scale), like emotional well-being, personal development, physical well-being, self-determination, and social inclusion, were greater after intervention (t ≥ -2.06, p < 0.05).

CONCLUSIONS

These findings underline the benefits of multi-component training in functionality of older adults, and further, provide relevant aspects about the modulation of pain perception, sleep disturbances, social factors and physical and emotional well-being. Physical exercise programs such as «Actívate» should be promoted, in order to encourage healthy lifestyle habits, in the older adults' population.

Loss of cortical control over the descending pain modulatory system determines the development of the neuropathic pain state in rats

The loss of descending inhibitory control is thought critical to the development of chronic pain but what causes this loss in function is not well understood. We have investigated the dynamic contribution of prelimbic cortical neuronal projections to the periaqueductal grey (PrL-P) to the development of neuropathic pain in rats using combined opto- and chemogenetic approaches. We found PrL-P neurons to exert a tonic inhibitory control on thermal withdrawal thresholds in uninjured animals. Following nerve injury, ongoing activity in PrL-P neurons masked latent hypersensitivity and improved affective state. However, this function is lost as the development of sensory hypersensitivity emerges. Despite this loss of tonic control, opto-activation of PrL-P neurons at late post-injury timepoints could restore the anti-allodynic effects by inhibition of spinal nociceptive processing. We suggest that the loss of cortical drive to the descending pain modulatory system underpins the expression of neuropathic sensitisation after nerve injury.

Pain modulatory network is influenced by sex and age in a healthy state and during osteoarthritis progression in rats

Old age and female sex are risk factors for the development of osteoarthritis (OA) and chronic pain. We investigated the effects of sex and age on pain modulatory networks in a healthy state and during OA progression. We used functional MRI to determine the effects of sex and age on periaqueductal gray functional connectivity (PAG FC) in a healthy state (pre‐OA) and during the early and late phases of monosodium iodoacetate‐induced OA in rats. We then examined how sex and age affect longitudinal changes in PAG FC in OA. In a healthy state, females exhibited more widespread PAG FC than males, and this effect was exaggerated with aging. Young males had moderate PAG FC changes during the early phase but recruited additional brain regions, including the rostral anterior cingulate cortex (ACC), during the late phase. Young females exhibited widespread PAG FC in the early phase, which includes connections to insula, caudal ACC, and nucleus accumbens (NAc). Older groups had strong PAG FC with fewer regions in the early phase, but they recruited additional brain regions, including NAc, in the late phase. Overall, our findings show that PAG FC is modulated by sex and age in a healthy state. A widespread PAG network in the early phase of OA pain may contribute to the transition from acute to chronic OA pain and the increased risk of developing chronic pain for females. Enhanced PAG FC with the reward system may represent a potential mechanism underlying chronic OA pain in elderly patients.