Neural basis of contagious itch and why some people are more prone to it

Department of Psychology, University of Hull, Hull HU6 7RX, United Kingdom.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 11/2012; 109(48). DOI: 10.1073/pnas.1216160109
Source: PubMed


Watching someone scratch himself can induce feelings of itchiness in the perceiver. This provides a unique opportunity to characterize the neural basis of subjective experiences of itch, independent of changes in peripheral inputs. In this study, we first established that the social contagion of itch is essentially a normative response (experienced by most people), and that the degree of contagion is related to trait differences in neuroticism (i.e., the tendency to experience negative emotions), but not to empathy. Watching video clips of someone scratching (relative to control videos of tapping) activated, as indicated by functional neuroimaging, many of the neural regions linked to the physical perception of itch, including anterior insular, primary somatosensory, and prefrontal (BA44) and premotor cortices. Moreover, activity in the left BA44, BA6, and primary somatosensory cortex was correlated with subjective ratings of itchiness, and the responsivity of the left BA44 reflected individual differences in neuroticism. Our findings highlight the central neural generation of the subjective experience of somatosensory perception in the absence of somatosensory stimulation. We speculate that the habitual activation of this central "itch matrix" may give rise to psychogenic itch disorders.

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Available from: Hugo Critchley, Oct 06, 2015
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    • "Plausibly, patients are less able to self-regulate responses to emotive stimuli and consequently experience intrusive thoughts and associated anxiety. Moreover, lateral prefrontal cortex is engaged during the experience of itch contagion (Holle et al., 2012), further highlighting relevance of top-down predictive influences on somatosensory control. Across both groups, we also found that viewing insect-related Fig. 2. Contrast estimates showing main effect of presentation of insect versus non insect images, skin images rather than leaf, activation of controls compared to patients and patients compared to controls and the contrast of the 3 way interaction. "
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    ABSTRACT: Some patients experience skin sensations of infestation and contamination that are elusive to proximate dermatological explanation. We undertook a functional magnetic resonance imaging study of the brain to demonstrate, for the first time, that central processing of infestation-relevant stimuli is altered in patients with such abnormal skin sensations. We show differences in neural activity within amygdala, insula, middle temporal lobe and frontal cortices. Patients also demonstrated altered measures of self-representation, with poorer sensitivity to internal bodily (interoceptive) signals and greater susceptibility to take on an illusion of body ownership: the rubber hand illusion. Together, these findings highlight a potential model for the maintenance of abnormal skin sensations, encompassing heightened threat processing within amygdala, increased salience of skin representations within insula and compromised prefrontal capacity for self-regulation and appraisal. Copyright © 2015. Published by Elsevier Ltd.
    Neuropsychologia 08/2015; DOI:10.1016/j.neuropsychologia.2015.08.006 · 3.30 Impact Factor
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    • "Other important areas to investigate are whether demographic variables like age and gender have an effect on this behavioral phenomenon. Because neuroticism is more pronounced in younger than in older adults (McCrae et al., 1999) and is associated with contagious itch (Holle et al., 2012), it would also be reasonable to assume that younger subjects are more susceptible to contagious itch. Also, we hypothesize that due to higher empathy (e.g., Wilson et al., 2012), women may be more susceptible to visual itch cues. "
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    ABSTRACT: All humans experience itch in the course of their life. Even a discussion on the topic of itch or seeing people scratch can evoke the desire to scratch. These events are coined “contagious itch” and are very common. We and others have shown that videos showing people scratching and pictures of affected skin or insects can induce itch in healthy persons and chronic itch patients. In our studies, patients with atopic dermatitis (AD) were more susceptible to visual itch cues than healthy. Also, personality traits like agreeableness and public self-consciousness were associated with induced scratching in skin patients, while neuroticism correlated with induced itch in healthy subjects. The underlying course of contagious itch is not yet fully understood. It is hypothesized that there are human mirror neurons that are active when we imitate actions and/or negative affect. Until now, there has been only limited data on the mechanisms of brain activation in contagious itch though. We have barely begun to understand the underlying physiological reactions and the triggering factors of this phenomenon. We summarize what we currently know about contagious itch and provide some suggestions what future research should focus on.
    Frontiers in Human Neuroscience 02/2015; 9. DOI:10.3389/fnhum.2015.00057 · 2.99 Impact Factor
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    • "During conditioning, the perception of an increase or decrease in sensations after a cue can shape both automatic and conscious expectations about the given cue [39], and with more or longer conditioning trials, the learned association may be more predictable. Moreover, the addition of explicit expectations (by verbal suggestion) might further amplify the induction of nocebo and placebo effects on physical sensations, and itch in particular which seems highly susceptible to suggestion as demonstrated by the phenomenon of “contagious” itch (e.g., [11], [12]). "
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    ABSTRACT: Placebo and nocebo effects are known to play a key role in treatment effects in a wide variety of conditions. These effects have frequently been investigated with regard to pain and also in other physical sensations, but have hardly been investigated with regard to itch. In addition, neither in pain nor in any other physical sensation, the single and combined contribution of the expectancy mechanisms of conditioning and verbal suggestion have ever been investigated in both placebo and nocebo effects within one design. For the first time, the role of verbal suggestion and conditioning in placebo and nocebo effects on itch was experimentally investigated. Expectations about itch stimuli were induced in healthy subjects by verbal suggestion, conditioning, or a combination of both procedures, and compared with a control group without expectation induction. Itch was induced electrically by means of quantitative sensory testing. Significant placebo and nocebo effects were induced in the group in which combined procedures of conditioning and verbal suggestion were applied in comparison with the control group. The conditioning and verbal suggestion procedures applied individually did not induce significant placebo and nocebo effects when compared with the control group. The results of this study extend existing evidence on different physical sensations, like pain, by showing that also for itch, the combination of conditioning and verbal suggestion is most promising in inducing both placebo and nocebo effects. More research on placebo and nocebo effects at a perceptive and neurobiological level is warranted to further elucidate the common and specific mechanisms underlying placebo and nocebo effects on itch and other physical sensations.
    PLoS ONE 03/2014; 9(3):e91727. DOI:10.1371/journal.pone.0091727 · 3.23 Impact Factor
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