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 to contextual fear and showed increased anxiety-like behavior. Additionally, SNI mice in comparison to sham animals exhibited hippocampal 1) reduced extracellular signal-regulated kinase (ERK) expression and phosphorylation, 2) decreased neurogenesis and 3) altered short-term synaptic plasticity. In order 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 to 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.

A meta-analysis of predictors of nonmarital romantic relationship dissolution was conducted, including data collected from 37,761 participants and 137 studies over 33 years. Individual, relationship, and external variables were investigated, and results suggest that commitment, love, inclusion of other in the self, and dependence were among the strongest predictors of dissolution. Other relational variables such as satisfaction, perceptions of alternatives, and investments were modest predictors of breakup, and the external factor of social network support was also a robust predictor. Personality measures were found to have limited predictive utility, with small effects found for dimensions relational in nature (e.g., adult attachment orientations). Theoretical and methodological implications are discussed within the context of future research on nonmarital relationship dissolution.Early research on close relationship processes focused primarily on attraction and relationship initiation (Berscheid & Reis, 1998), but in the past 25 years, research on other topics has burgeoned. The stability of relationships is of particular interest to researchers,

The hippocampus has been shown to undergo significant changes in rodent models of neuropathic pain; however, the role of the hippocampus in human chronic pain and its contribution to pain chronification have remained unexplored. Here we examine hippocampal processing during a simple visual attention task. We used functional MRI to identify intrinsic and extrinsic hippocampal functional connectivity (synchronous neural activity), comparing subacute back pain (SBP, back pain 1-4 mo) and chronic back pain (CBP, back pain >10 yr) patients to control (CON) subjects. Both groups showed more extensive hippocampal connectivity than CON subjects. We then examined the evolution of hippocampal connectivity longitudinally in SBP patients who recovered (SBPr, back pain decreased >20% in 1 yr) and those with persistent pain (SBPp). We found that SBPp and SBPr subjects have distinct changes in hippocampal-cortical connectivity over 1 yr; specifically, SBPp subjects showed large decreases in hippocampal connectivity with medial prefrontal cortex (HG-mPFC). Furthermore, in SBP patients the strength of HG-mPFC reflected variations in back pain over the year. These relationships were replicated when examined in a different task performed by SBP patients (rating fluctuations of back pain), indicating that functional connectivity of the hippocampus changes robustly in subacute pain and the nature of these changes depends on whether or not patients recover from SBP. The observed reorganization of processing within the hippocampus and between the hippocampus and the cortex seems to contribute to the transition from subacute to chronic pain and may also underlie learning and emotional abnormalities associated with chronic pain.

It has been recently demonstrated that pain behavior in the mouse can be modulated by the presence of a conspecific, but what remains unclear is whether such pain behavior can serve the function of soliciting social approach. Using a novel social approach paradigm, we tested mice in various dyadic or triadic conditions, including "jailed" mice-some in pain via intraperitoneal injection of 0.9% acetic acid-and test mice free to approach or avoid the jailed mice. We observed a sex-specific effect whereby female, but not male, test mice approached a familiar same-sex conspecific in pain more frequently than an unaffected familiar or unfamiliar, but affected, conspecific. Despite a substantial literature emphasizing oxytocin's role in affiliative and pair-bonding behavior, this effect was also observed in female mice lacking the oxytocin receptor, suggesting that pain-related social approach may not be mediated by oxytocin. Furthermore, we found that the frequency of contact by the test mouse was negatively correlated with the pain behavior of the jailed mouse, suggesting that proximity of a familiar unaffected conspecific may have analgesic properties.

The full role of adult hippocampal neurogenesis (AHN) remains to be determined, yet it is implicated in learning and emotional functions, and is disrupted in negative mood disorders. Recent evidence indicates that AHN is decreased in persistent pain consistent with the idea that chronic pain is a major stressor, associated with negative moods and abnormal memories. Yet, the role of AHN in development of persistent pain has remained unexplored. In this study, we test the influence of AHN in postinjury inflammatory and neuropathic persistent pain-like behaviors by manipulating neurogenesis: pharmacologically through intracerebroventricular infusion of the antimitotic AraC; ablation of AHN by x-irradiation; and using transgenic mice with increased or decreased AHN. Downregulating neurogenesis reversibly diminished or blocked persistent pain; oppositely, upregulating neurogenesis led to prolonged persistent pain. Moreover, we could dissociate negative mood from persistent pain. These results suggest that AHN-mediated hippocampal learning mechanisms are involved in the emergence of persistent pain.