Intrinsic functional connectivity of insular cortex and symptoms of sickness during acute experimental inflammation

Pilot investigation into the sickness response to influenza vaccination in adults: Effect of depression and anxiety

OBJECTIVE

To determine whether depressed or anxious patients experience greater affective change than mentally healthy individuals following influenza vaccination.

METHODS

Participants (n=112) completed the Positive and Negative Affect Schedule (PANAS) before influenza vaccination and 1-2days post-vaccination (M=32.3h). Pre- and post-vaccination PANAS scores were compared using two-tailed, paired-samples t-tests. Change in positive affect between participants with depression or anxiety and those without was compared using two-way ANOVA. Follow up positive affect was further examined using multiple linear regression.

RESULTS

Positive affect decreased following vaccination (M=2.18, 95% CI [1.07, 3.29], t(111)=3.89, p<0.001) for all participants and was more pronounced for those with anxiety or depression (F(1, 110)=7.51, p=0.009). Similarly, predicted follow up affect score was higher for those without a mental health conditions (β=3.67, 95% CI [1.18, 6.16], t(103)=2.92, p=0.004).

CONCLUSIONS

These data suggest that influenza vaccine has a greater effect on affect in patients with depression and anxiety than in mentally healthy individuals. This effect was focused on positive affect, suggesting that influenza vaccine induced inflammation may be best suited to examine alterations in positive affect and positive valence systems.

Behavioral and neural correlates to multisensory detection of sick humans

Throughout human evolution, infectious diseases have been a primary cause of death. Detection of subtle cues indicating sickness and avoidance of sick conspecifics would therefore be an adaptive way of coping with an environment fraught with pathogens. This study determines how humans perceive and integrate early cues of sickness in conspecifics sampled just hours after the induction of immune system activation, and the underlying neural mechanisms for this detection. In a double-blind placebo-controlled crossover design, the immune system in 22 sample donors was transiently activated with an endotoxin injection [lipopolysaccharide (LPS)]. Facial photographs and body odor samples were taken from the same donors when "sick" (LPS-injected) and when "healthy" (saline-injected) and subsequently were presented to a separate group of participants (n = 30) who rated their liking of the presented person during fMRI scanning. Faces were less socially desirable when sick, and sick body odors tended to lower liking of the faces. Sickness status presented by odor and facial photograph resulted in increased neural activation of odor- and face-perception networks, respectively. A superadditive effect of olfactory-visual integration of sickness cues was found in the intraparietal sulcus, which was functionally connected to core areas of multisensory integration in the superior temporal sulcus and orbitofrontal cortex. Taken together, the results outline a disease-avoidance model in which neural mechanisms involved in the detection of disease cues and multisensory integration are vital parts.

A Comparison of Neuroimaging Abnormalities in Multiple Sclerosis, Major Depression and Chronic Fatigue Syndrome (Myalgic Encephalomyelitis): is There a Common Cause?

There is copious evidence of abnormalities in resting-state functional network connectivity states, grey and white matter pathology and impaired cerebral perfusion in patients afforded a diagnosis of multiple sclerosis, major depression or chronic fatigue syndrome (CFS) (myalgic encephalomyelitis). Systemic inflammation may well be a major element explaining such findings. Inter-patient and inter-illness variations in neuroimaging findings may arise at least in part from regional genetic, epigenetic and environmental variations in the functions of microglia and astrocytes. Regional differences in neuronal resistance to oxidative and inflammatory insults and in the performance of antioxidant defences in the central nervous system may also play a role. Importantly, replicated experimental findings suggest that the use of high-resolution SPECT imaging may have the capacity to differentiate patients afforded a diagnosis of CFS from those with a diagnosis of depression. Further research involving this form of neuroimaging appears warranted in an attempt to overcome the problem of aetiologically heterogeneous cohorts which probably explain conflicting findings produced by investigative teams active in this field. However, the ionising radiation and relative lack of sensitivity involved probably preclude its use as a routine diagnostic tool.

What Makes You Feel Sick After Inflammation? Predictors of Acute and Persisting Physical Sickness Symptoms Induced by Experimental Endotoxemia

We aimed to identify statistical predictor variables of lipopolysaccharide (LPS)-induced physical sickness symptoms during the acute and late inflammatory phases using multivariate regression analyses. Data from N = 128 healthy volunteers who received i.v. LPS injection (0.4 or 0.8 ng/kg) or placebo were pooled for analyses. Physical sickness symptoms experienced during the acute (0-6h postinjection) and late (6-24h postinjection) phases were assessed with the validated General-Assessment-of-Side-Effects (GASE) questionnaire. LPS-treated subjects reported significantly more physical sickness symptoms. Physical symptoms during the acute phase were associated with LPS-induced mood impairments and interleukin (IL)-6 increases, explaining 28.5% of variance in GASE scores. During late phase, LPS-induced increases in cortisol and IL-6 plasma concentrations and baseline depression were significant predictor variables, explaining 38.5% of variance. In patients with recurrent or chronic inflammatory states, these factors may act as risk factors ultimately contributing to an exacerbation of sickness symptoms, and should be considered as potential targets for therapeutic strategies.

Role of Inflammation in Human Fatigue: Relevance of Multidimensional Assessments and Potential Neuronal Mechanisms

Fatigue is a highly disabling symptom in various medical conditions. While inflammation has been suggested as a potential contributor to the development of fatigue, underlying mechanisms remain poorly understood. In this review, we propose that a better assessment of central fatigue, taking into account its multidimensional features, could help elucidate the role and mechanisms of inflammation in fatigue development. A description of the features of central fatigue is provided, and the current evidence describing the association between inflammation and fatigue in various medical conditions is reviewed. Additionally, the effect of inflammation on specific neuronal processes that may be involved in distinct fatigue dimensions is described. We suggest that the multidimensional aspects of fatigue should be assessed in future studies of inflammation-induced fatigue and that this would benefit the development of effective therapeutic interventions.

Brain Structures Implicated in Inflammation-Associated Depression

Systemic inflammation rapidly impairs mood, motivation, and cognition inducing a stereotyped cluster of symptoms collectively known as "sickness behaviors." When inflammation is severe or chronic, these behavioral changes can appear indistinguishable from major depressive disorder (MDD). Human and rodent neuroimaging combined with experimental inflammatory challenges has clarified the neural circuitry associated with many of the key features of inflammation-induced-sickness behavior, and in so doing revealed often-remarkable commonalities with circuit abnormalities observed in MDD. This review aims to provide the first synthesis of this work illustrating areas of convergence and divergence with the MDD literature as well as highlighting areas for future study.

Commentary on the 2016 named series: Neuroimaging, inflammation and behavior

Neuroimaging techniques are increasingly used to characterize the neural circuitry mediating actions of inflammation on mood, motivation, and cognition and its relationship to common mental illnesses, particularly major depressive disorder (MDD). In addition, imaging techniques such as single photon emission tomography (SPECT), positron emission tomography (PET) and magnetic resonance spectroscopy (MRS) can index effects of inflammation on specific neurotransmitters, monoamine transporters, metabolites and even activation of discrete cells such as microglia. The special named series 'Neuroimaging, inflammation and behavior' illustrates the power of neuroimaging techniques to characterize discrete actions of inflammation on the brain at neurochemical, cellular, regional and network levels. Combined with careful cognitive assessment and pre-clinical studies, diverse neuroimaging techniques are helping clarify the mechanisms through which inflammation acts on the brain to reorient behavior and predispose to mental and physical illnesses.