Hippocampal correlates of pain in healthy elderly adults: a pilot study

Does cognitive functioning predict chronic pain? Results from a prospective surgical cohort

It is well established that chronic pain impairs cognition, particularly memory, attention and mental flexibility. Overlaps have been found between the brain regions involved in pain modulation and cognition, including in particular the prefrontal cortex and the anterior cingulate cortex, which are involved in executive function, attention and memory. However, whether cognitive function may predict chronic pain has not been investigated. We addressed this question in surgical patients, because such patients can be followed prospectively and may have no pain before surgery. In this prospective longitudinal study, we investigated the links between executive function, visual memory and attention, as assessed by clinical measurements and the development of chronic pain, its severity and neuropathic symptoms (based on the 'Douleur Neuropathique 4' questionnaire), 6 and 12 months after surgery (total knee arthroplasty for osteoarthritis or breast surgery for cancer). Neuropsychological tests included the Trail-Making Test A and B, and the Rey-Osterrieth Complex Figure copy and immediate recall, which assess cognitive flexibility, visuospatial processing and visual memory. Anxiety, depression and coping strategies were also evaluated. In total, we investigated 189 patients before surgery: 96% were re-evaluated at 6 months, and 88% at 12 months. Multivariate logistic regression (stepwise selection) for the total group of patients indicated that the presence of clinical meaningful pain at 6 and 12 months (pain intensity ≥ 3/10) was predicted by poorer cognitive performance in the Trail Making Test B (P = 0.0009 and 0.02 for pain at 6 and 12 months, respectively), Rey-Osterrieth Complex Figure copy (P = 0.015 and 0.006 for pain at 6 and 12 months, respectively) and recall (P = 0.016 for pain at 12 months), independently of affective variables. Linear regression analyses indicated that impaired scores on these tests predicted pain intensity (P < 0.01) and neuropathic symptoms in patients with pain (P < 0.05), although the strength of the association was less robust for neuropathic symptoms. These results were not affected by the type of surgery or presurgical pain, similar findings being obtained specifically for patients who initially had no pain. In conclusion, these findings support, for the first time, the notion that premorbid limited cognitive flexibility and memory capacities may be linked to the mechanisms of pain chronicity and probably also to its neuropathic quality. This may imply that patients with deficits in executive functioning or memory because of cerebral conditions have a greater risk of pain chronicity after a painful event.

Hippocampal correlates of depression in healthy elderly adults

Mixed findings have been reported on the relationship between hippocampal integrity and major depression in clinical populations. Few neuroimaging studies have investigated associations between hippocampal measures and depressive symptoms in nondemented older adults. Here, we address this issue by imaging 36 nondemented adults over age 70 from the Einstein Aging Study, a community-based sample from the Bronx, NY. Depressive symptoms were assessed using the 15-item Geriatric Depression scale (GDS). Clinically significant depression was defined using a cut-off score of 5 or greater. Hippocampal data included MRI-derived volume data normalized to midsagittal area and MRS-derived N-acetylaspartate to creatine ratios (NAA/Cr). Our result indicates that smaller total hippocampal volume was associated with higher GDS scores, but there were no significant association between hippocampal NAA/Cr and GDS score. These effects were consistent after controlling for age, education, and gender. Reduction in hippocampal volume could represent a risk factor or a consequence of depression in older adults. Further studies are needed to better understand the role of the hippocampus in the development and experience of depression in older adults.

Reduced N-acetylaspartate in the hippocampus in patients with fibromyalgia: a meta-analysis

Fibromyalgia (FM) is a stress-associated syndrome with chronic, widespread pain. Patients with FM also present disturbances of cognition and memory. As the hippocampus is vulnerable to stress exposure and involved in cognition, memory and pain perception, we hypothesize that the abnormal function of the hippocampus is implicated in the pathophysiology of FM. N-acetylaspartate (NAA), a metabolite that can be measured using proton magnetic resonance spectroscopy (1H MRS), is recognized as a marker of neuronal structure and function. We performed a systematic review and meta-analysis of 1H MRS studies investigating NAA levels in patients with FM. A comprehensive literature search through MEDLINE, Embase and Web of Science yielded nine studies; among these nine, four studies met our criteria for inclusion. A random effect model with 51 patients with FM and 38 controls revealed a significant NAA reduction in the hippocampus. The current meta-analysis suggested a neuronal abnormality in the hippocampus in patients with FM.

Common hippocampal structural and functional changes in migraine

The hippocampus is classically involved in memory consolidation, spatial navigation and is involved in the stress response. Migraine is an episodic disorder characterized by intermittent attacks with a number of physiological and emotional stressors associated with or provoking each attack. Given that migraine attacks can be viewed as repeated stressors, alterations in hippocampal function and structure may play an important role in migraine pathophysiology. Using high-resolution magnetic resonance imaging, hippocampal morphometric and functional differences (in response to noxious heat stimulation) were compared in age and gender-matched acute episodic migraineurs with high (HF) versus low (LF) frequency of migraine attacks. Morphometric results were compared with age and gender-matched healthy control (HC) cohort. Significant larger bilateral hippocampal volume was found in LF group relative to the HF and HC groups suggestive of an initial adaptive plasticity that may then become dysfunctional with increased frequency. Functional correlates of greater deactivation (LF > HF) in the same hippocampal regions in response to noxious stimulation was also accompanied by overall reduction in functional connectivity of the hippocampus with other brain regions involved in pain processing in the HF group. The results implicate involvement of hippocampus in the pathophysiology of the migraine.

Abnormalities in hippocampal functioning with persistent pain

Chronic pain patients exhibit increased anxiety, depression, and deficits in learning and memory. Yet how persistent pain affects the key brain area regulating these behaviors, the hippocampus, has remained minimally explored. In this study we investigated the impact of spared nerve injury (SNI) neuropathic pain in mice on hippocampal-dependent behavior and underlying cellular and molecular changes. In parallel, we measured the hippocampal volume of three groups of chronic pain patients. We found that SNI animals were unable to extinguish contextual fear and showed increased anxiety-like behavior. Additionally, SNI mice compared with Sham animals exhibited hippocampal (1) reduced extracellular signal-regulated kinase expression and phosphorylation, (2) decreased neurogenesis, and (3) altered short-term synaptic plasticity. To relate the observed hippocampal abnormalities with human chronic pain, we measured the volume of human hippocampus in chronic back pain (CBP), complex regional pain syndrome (CRPS), and osteoarthritis patients (OA). Compared with controls, CBP and CRPS, but not OA, had significantly less bilateral hippocampal volume. These results indicate that hippocampus-mediated behavior, synaptic plasticity, and neurogenesis are abnormal in neuropathic rodents. The changes may be related to the reduction in hippocampal volume we see in chronic pain patients, and these abnormalities may underlie learning and emotional deficits commonly observed in such patients.

The brain in chronic pain: clinical implications

This article examines the present, and potential future, impact of brain imaging on chronic pain. It is argued that novel theories of chronic pain are coming to the fore, specifically through brain imaging of the human brain in chronic pain. Such studies show that the brain reorganizes in relation to chronic pain, in a pattern specific to the type of clinical pain, and that brain networks and receptor targets are being identified and reverse translated to animal studies of their efficacy and mechanisms. Future studies need to integrate across human brain imaging techniques, as well as more intensive reverse translational methods.

Dysmenorrhoea is associated with central changes in otherwise healthy women

Patients with chronic pain conditions demonstrate altered central processing of experimental noxious stimuli, dysfunction of the hypothalamic-pituitary-adrenal axis, and reduced quality of life. Dysmenorrhoea is not considered a chronic pain condition, but is associated with enhanced behavioural responses to experimental noxious stimuli. We used behavioural measures, functional magnetic resonance imaging, and serum steroid hormone levels to investigate the response to experimental thermal stimuli in otherwise healthy women, with and without dysmenorrhoea. Women with dysmenorrhoea reported increased pain to noxious stimulation of the arm and abdomen throughout the menstrual cycle; no menstrual cycle effect was observed in either group. During menstruation, deactivation of brain regions in response to noxious stimulation was observed in control women but not in women with dysmenorrhoea. Without background pain (ie, in nonmenstrual phases), activity in the entorhinal cortex appeared to mediate the increased responses in women with dysmenorrhoea. Mean cortisol was significantly lower in women with dysmenorrhoea and was negatively correlated with the duration of the symptom. Additionally, women with dysmenorrhoea reported significantly lower physical but not mental quality of life. Thus, many features of chronic pain conditions are also seen in women with dysmenorrhoea: specifically a reduction in quality of life, suppression of the hypothalamic-pituitary-adrenal axis, and alterations in the central processing of experimental noxious stimuli. These alterations persist when there is no background pain and occur in response to stimuli at a site distant from that of the clinical pain. These findings indicate the potential importance of early and adequate treatment of dysmenorrhoea.

Pain imaging in health and disease--how far have we come?

Since modern brain imaging of pain began 20 years ago, networks in the brain related to pain processing and those related to different types of pain modulation, including placebo, have been identified. Functional and anatomical connectivity of these circuits has begun to be analyzed. Imaging in patients suggests that chronic pain is associated with altered function and structural abnormalities in pain modulatory circuits. Moreover, biochemical alterations associated with chronic pain are being identified that provide information on cellular correlates as well as potential mechanisms of structural changes. Data from these brain imaging studies reinforce the idea that chronic pain leads to brain changes that could have functional significance.