Alteration of delay and trace eyeblink conditioning in fibromyalgia patients

Brain Circuits Involved in the Development of Chronic Musculoskeletal Pain: Evidence From Non-invasive Brain Stimulation

It has been well-documented that the brain changes in states of chronic pain. Less is known about changes in the brain that predict the transition from acute to chronic pain. Evidence from neuroimaging studies suggests a shift from brain regions involved in nociceptive processing to corticostriatal brain regions that are instrumental in the processing of reward and emotional learning in the transition to the chronic state. In addition, dysfunction in descending pain modulatory circuits encompassing the periaqueductal gray and the rostral anterior cingulate cortex may also be a key risk factor for pain chronicity. Although longitudinal imaging studies have revealed potential predictors of pain chronicity, their causal role has not yet been determined. Here we review evidence from studies that involve non-invasive brain stimulation to elucidate to what extent they may help to elucidate the brain circuits involved in pain chronicity. Especially, we focus on studies using non-invasive brain stimulation techniques [e.g., transcranial magnetic stimulation (TMS), particularly its repetitive form (rTMS), transcranial alternating current stimulation (tACS), and transcranial direct current stimulation (tDCS)] in the context of musculoskeletal pain chronicity. We focus on the role of the motor cortex because of its known contribution to sensory components of pain via thalamic inhibition, and the role of the dorsolateral prefrontal cortex because of its role on cognitive and affective processing of pain. We will also discuss findings from studies using experimentally induced prolonged pain and studies implicating the DLPFC, which may shed light on the earliest transition phase to chronicity. We propose that combined brain stimulation and imaging studies might further advance mechanistic models of the chronicity process and involved brain circuits. Implications and challenges for translating the research on mechanistic models of the development of chronic pain to clinical practice will also be addressed.

Neural circuitry underlying effects of context on human pain-related fear extinction in a renewal paradigm

OBJECTIVES

The role of context in pain-related extinction learning remains poorly understood. We analyzed the neural mechanisms underlying context-dependent extinction and renewal in a clinically relevant model of conditioned abdominal pain-related fear.

EXPERIMENTAL DESIGN

In this functional magnetic resonance imaging study, two groups of healthy volunteers underwent differential fear conditioning with painful rectal distensions as unconditioned stimuli (US) and visual conditioned stimuli (CS(+) ; CS(-) ). The extinction context was changed in an experimental group (context group), which was subsequently returned into the original learning context to test for renewal. No context changes occurred in the control group. Group differences in CS-induced differential neural activation were analyzed along with skin conductance responses (SCR), CS valence and CS-US contingency ratings.

PRINCIPAL OBSERVATIONS

During extinction, group differences in differential neural activation were observed in dorsolateral (dlPFC) and ventromedial (vmPFC) prefrontal cortex and amygdala, mainly driven by enhanced activation in response to the CS(-) in the control group. During renewal, observed group differences in activation of dlPFC and orbitofrontal cortex (OFC) resulted primarily from differential modulation of the CS(-) in the absence of group differences in response to CS(+) or SCR.

CONCLUSION

The extinction context affects the neural processing of nonpain predictive safety cues, supporting a role of safety learning in pain-related memory processes.

Neural circuitry of abdominal pain-related fear learning and reinstatement in irritable bowel syndrome

BACKGROUND

Altered pain anticipation likely contributes to disturbed central pain processing in chronic pain conditions like irritable bowel syndrome (IBS), but the learning processes shaping the expectation of pain remain poorly understood. We assessed the neural circuitry mediating the formation, extinction, and reactivation of abdominal pain-related memories in IBS patients compared to healthy controls (HC) in a differential fear conditioning paradigm.

METHODS

During fear acquisition, predictive visual cues (CS(+)) were paired with rectal distensions (US), while control cues (CS(-)) were presented unpaired. During extinction, only CSs were presented. Subsequently, memory reactivation was assessed with a reinstatement procedure involving unexpected USs. Using functional magnetic resonance imaging, group differences in neural activation to CS(+) vs CS(-) were analyzed, along with skin conductance responses (SCR), CS valence, CS-US contingency, state anxiety, salivary cortisol, and alpha-amylase activity. The contribution of anxiety symptoms was addressed in covariance analyses.

KEY RESULTS

Fear acquisition was altered in IBS, as indicated by more accurate contingency awareness, greater CS-related valence change, and enhanced CS(+)-induced differential activation of prefrontal cortex and amygdala. IBS patients further revealed enhanced differential cingulate activation during extinction and greater differential hippocampal activation during reinstatement. Anxiety affected neural responses during memory formation and reinstatement.

CONCLUSIONS & INFERENCES

Abdominal pain-related fear learning and memory processes are altered in IBS, mediated by amygdala, cingulate cortex, prefrontal areas, and hippocampus. Enhanced reinstatement may contribute to hypervigilance and central pain amplification, especially in anxious patients. Preventing a 'relapse' of learned fear utilizing extinction-based interventions may be a promising treatment goal in IBS.

For whom the bell (curve) tolls: cortisol rapidly affects memory retrieval by an inverted U-shaped dose-response relationship

Stress and cortisol are generally considered to impair declarative memory retrieval, although opposite results have also been reported. Dose-dependent effects and differences between genomic and non-genomic cortisol effects are possible reasons for these discrepancies. The aim of the current experiment was to assess the non-genomic effects of escalating doses of intravenous cortisol on cued recall of socially relevant information in humans. 40 participants (age range 20-30 years; 20 females) learned associations between male faces with a neutral facial expression and descriptions of either positive or negative social behaviors and were tested one week later in a cued recall paradigm. Escalating doses of cortisol (0, 3, 6, 12, 24 mg) were administered 8 min before testing according to a between-subjects design. An inverted U-shaped dose-response relationship between salivary cortisol levels and recall performance was observed, with moderate elevation of salivary cortisol resulting in the best recall performance. This is the first study in humans demonstrating that cortisol rapidly modulates declarative memory retrieval via a dose-dependent, non-genomic mechanism that follows an inverted U-shaped curve. Our result further emphasizes the importance of fast cortisol effects for human cognition.

Fear conditioning in an abdominal pain model: neural responses during associative learning and extinction in healthy subjects

Fear conditioning is relevant for elucidating the pathophysiology of anxiety, but may also be useful in the context of chronic pain syndromes which often overlap with anxiety. Thus far, no fear conditioning studies have employed aversive visceral stimuli from the lower gastrointestinal tract. Therefore, we implemented a fear conditioning paradigm to analyze the conditioned response to rectal pain stimuli using fMRI during associative learning, extinction and reinstatement.

In N = 21 healthy humans, visual conditioned stimuli (CS⁺) were paired with painful rectal distensions as unconditioned stimuli (US), while different visual stimuli (CS⁻) were presented without US. During extinction, all CSs were presented without US, whereas during reinstatement, a single, unpaired US was presented. In region-of-interest analyses, conditioned anticipatory neural activation was assessed along with perceived CS-US contingency and CS unpleasantness.

Fear conditioning resulted in significant contingency awareness and valence change, i.e., learned unpleasantness of a previously neutral stimulus. This was paralleled by anticipatory activation of the anterior cingulate cortex, the somatosensory cortex and precuneus (all during early acquisition) and the amygdala (late acquisition) in response to the CS⁺. During extinction, anticipatory activation of the dorsolateral prefrontal cortex to the CS⁻ was observed. In the reinstatement phase, a tendency for parahippocampal activation was found.

Fear conditioning with rectal pain stimuli is feasible and leads to learned unpleasantness of previously neutral stimuli. Within the brain, conditioned anticipatory activations are seen in core areas of the central fear network including the amygdala and the anterior cingulate cortex. During extinction, conditioned responses quickly disappear, and learning of new predictive cue properties is paralleled by prefrontal activation. A tendency for parahippocampal activation during reinstatement could indicate a reactivation of the old memory trace. Together, these findings contribute to our understanding of aversive visceral learning and memory processes relevant to the pathophysiology of chronic abdominal pain.

Circadian rhythm of serum cortisol in female patients with fibromyalgia syndrome

Fibromyalgia syndrome (FMS) patients have disturbed sleep patterns which may lead to altered circadian rhythm in serum cortisol secretion. The aim of this study was to assess circadian changes, if any, in serum cortisol levels in female patients with FMS. Cortisol levels were estimated every 6 h during 24 h period; in 40 female patients satisfying ACR criteria for FMS (Age 36.4 ± 9.9), and 40 healthy females without FMS (Age 33.8 ± 11.1). A significant difference in the night time serum cortisol level was observed among the patients and control groups (patients, 12.9 ± 9.7 controls 5.8 ± 3.0; p < 0.01). However, no significant difference was found in serum cortisol levels in patients and control groups in the morning (patients, 28.4 ± 13.2 controls, 27.6 ± 14.5; p > 0.05), afternoon (patients, 14.4 ± 5.6 controls, 14.0 ± 6.6; p > 0.05) and evening hours (patients, 10.9 ± 5.8 controls, 8.9 ± 3.6; p > 0.05). It could be concluded that there is an abnormality in circadian secretion of cortisol in female FMS patients.

Oral cortisol impairs implicit sequence learning

RATIONALE

Glucocorticoids have been shown to affect declarative memory, an explicit form of memory for facts and events operated by medial temporal lobe structures. Recent neuroimaging data suggest that the medial temporal lobe (including the hippocampus) is also active in implicit sequence learning.

OBJECTIVES

The aim of the present study was to investigate whether implicit sequence learning may also be affected by glucocorticoid administration.

METHODS

Oral cortisol (30 mg) was given to 29 healthy subjects whereas 31 control subjects received placebo. One hour after treatment all volunteers performed five consecutive blocks of a five-choice serial reaction time task by responding to colored lights by pressing buttons of the same color. The subjects responded without knowing to a quasi-randomized stimulus sequence, including higher-order sequential regularities (a combination of two colors that predicted the following target color). The reaction speed of every button-press (100 per block) was determined and difference scores were calculated as a proof of learning.

RESULTS

Both groups showed significant implicit sequence learning throughout the experiment. However, we found an impaired learning performance of the cortisol group compared with the placebo group. Further analysis revealed that a delayed learning in the cortisol group occurred at the very beginning of the task.

CONCLUSIONS

This study is the first human investigation indicating impaired implicit memory function after exogenous administration of the stress hormone cortisol. This effect may depend on hippocampus engagement in implicit sequence learning, but the involvement of other brain structures is also discussed.

Abdominal pain in Irritable Bowel Syndrome: a review of putative psychological, neural and neuro-immune mechanisms

Chronic abdominal pain is a common symptom of great clinical significance in several areas of medicine. In many cases no organic cause can be established resulting in the classification as functional gastrointestinal disorder. Irritable Bowel Syndrome (IBS) is the most common of these conditions and is considered an important public health problem because it can be disabling and constitutes a major social and economic burden given the lack of effective treatments. IBS aetiology is most likely multi-factorial involving biological, psychological and social factors. Visceral hyperalgesia (or hypersensitivity) and visceral hypervigilance, which could be mediated by peripheral, spinal, and/or central pathways, constitute key concepts in current research on pathophysiological mechanisms of visceral hyperalgesia. The role of central nervous system mechanisms along the "brain-gut axis" is increasingly appreciated, owing to accumulating evidence from brain imaging studies that neural processing of visceral stimuli is altered in IBS together with long-standing knowledge regarding the contribution of stress and negative emotions to symptom frequency and severity. At the same time, there is also growing evidence suggesting that peripheral immune mechanisms and disturbed neuro-immune communication could play a role in the pathophysiology of visceral hyperalgesia. This review presents recent advances in research on the pathophysiology of visceral hyperalgesia in IBS, with a focus on the role of stress and anxiety in central and peripheral response to visceral pain stimuli. Together, these findings support that in addition to lower pain thresholds displayed by a significant proportion of patients, the evaluation of pain appears to be altered in IBS. This may be attributable to affective disturbances, negative emotions in anticipation of or during visceral stimulation, and altered pain-related expectations and learning processes. Disturbed "top-down" emotional and cognitive pain modulation in IBS is reflected by functional and possibly structural brain changes involving prefrontal as well as cingulate regions. At the same time, there is growing evidence linking peripheral and mucosal immune changes and abdominal pain in IBS, supporting disturbed peripheral pain signalling. Findings in post-infectious IBS emphasize the interaction between centrally-mediated psychosocial risk factors and local inflammation in predicting long-term IBS symptoms. Investigating afferent immune-to-brain communication in visceral hyperalgesia as a component of the sickness response constitutes a promising future research goal.