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See also Commentary, p. 1064 INVESTIGATIVE REPORT ActaDV ActaDV Advances in dermatology and venereology Acta Dermato-Venereologica
Distraction From Itch Shows Brainstem Activation Without Reduction in Experimental Itch Sensation
Astrid STUMPF 1, 2, Bettina PFLEIDERER 2, 3, Gudrun SCHNEIDER 1, 2, Gereon HEUFT 1, 2, Martin SCHMELZ 4, Ngoc Quan PHAN 2, 5, Sonja STÄNDER 2, 5 and Markus BURGMER 1, 2
1
Department of Psychosomatics and Psychotherapy, 2 Center for Chronic Pruritus( KCP), 3 Department of Clinical Radiology and 5 Department of Dermatology, University of Münster, Münster, and 4 Department of Anesthesiology and Intensive Care Medicine, Karl Feuerstein Professorship, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany
The central processing of itch is not completely understood. This is the first study to use functional magnetic resonance imaging( fMRI) to examine the central modulation by distraction of experimentally induced itch. A total of 33 healthy volunteers were examined with fMRI. Periods of itch induction without distraction and itch with distraction by a Stroop task( psychological test, where the participants have to decide if the colour of the writing corresponds to the written word, for example if“ red” is written in red or not) were counterbalanced during the scanning to examine task-specific changes in blood oxygenation level dependent-signal. The intensity of the subjects’ itch sensation, desire to scratch and pain sensation were evaluated. Distraction by a Stroop task did not reduce itch intensity or urge to scratch. However, the Stroop task led to significantly higher activation of the left brainstem when it followed the“ pure” itch sensation. Itch and pain seem to have similar inhibition pathways, particularly concerning brainstem activation during distraction. But as itch sensation, in contrast to pain, could not be sufficiently reduced by distraction, both entities might have different modulation systems.
Key words: fMRI; itch; scratch; pain; pain inhibition system. Acta Derm Venereol 2017; 97: 1074 – 1080. Accepted Jun 22, 2017; Epub ahead of print Jun 27, 2017
Corr: Astrid Stumpf, Department of Psychosomatics and Psychotherapy, University of Münster, Domagkstrasse 22, DE-48149 Münster, Germany. E-mail: astrid. stumpf @ ukmuenster. de
Itch and pain are unpleasant sensory experiences that have many characteristics in common. Paralleling clinical pain( 1, 2), itch leads to a huge reduction in quality of life and thus can provoke comorbidities such as anxiety disorders or depression( 3 – 5). Like chronic pain, the treatment of chronic itch is often insufficient and represents a challenge for the physician( 6 – 9).
During recent years, our knowledge of central processing and modulation of itch has increased. Positron emission tomography( PET) and functional magnetic resonance imaging( fMRI) during experimental itch stimulation have revealed activation of brain regions responsible for motor planning, sensory aspects and emotional processes( 10 – 20). The activation patterns of itch and pain overlap to a great extent. However, relative increases in different brain areas may differ. For example, itch-induced activation of the somatosensory areas SI and SII appears to be weaker, whereas activation of motor areas is stronger( 21). Moreover, stronger activation of the anterior cingulate cortex( ACC) and insula was observed in experimental pain conditions.
Cognitive attention to, or distraction from, pain are important in pain modulation( 22 – 26) in particular to shift the subject’ s attention away from clinical pain( 27, 28) and, accordingly, reducing its intensity. On a neurobiological level, pain modulation correlates with a profound interaction between central pain-encoding and pain-inhibiting areas( 24, 26, 29). In particular, the frontal lobe, the anterior cingulate cortex, the hypothalamus, the insula and the brainstem( nucleus cuneiformis( NCF), and the periaqueductal grey( PAG)) are involved in the descending modulation of pain( 30).
Distraction not only leads to a reduction in the intensity of pain( 31, 32), but also of itch( 33). The neurobiological background of this phenomenon in itch is unknown. Mochizuki et al.( 16) showed that itch can be reduced by painful stimuli, leading to an activation of the PAG. In contrast, Papoiu et al.( 34) postulated that itch modulation might be contrary to mechanisms known to suppress pain. They found an activation of the reward system( namely the ventral tegmentum) that led to a deactivation of the PAG. A few studies have examined the effect of drugs on itch modulation. Naltrexone( 35) reduced fMRI activity during itch perception induced by histamine or capsaicin, while butorphanol suppressed only histamine-induced itch. In the latter condition, structures of the mesolimbic circuit seemed to play an important role during itch suppression( 36). As the PAG seems to play not only an important role in pain modulation( by distraction), but also in itch modulation, we examined the activity of the PAG and the NCF during itch with and without distraction. In line with results from the pain field, we hypothesized that comparable activation of brainstem areas and a decrease in itch sensation during distraction should occur. This paper provides additional analyses based on imaging data published in 2013 from our working group( 37). Here, we focus on the effects of distraction on activity in the PAG and NCF. In our previous paper, sex-specific differences were observed in localization and itch perception( 37). Since no sex-differences were found for itch sensation and brain activity during distraction, data for male and female subjects were pooled in this paper. doi: 10.2340 / 00015555-2732 Acta Derm Venereol 2017; 97: 1074 – 1080
This is an open access article under the CC BY-NC license. www. medicaljournals. se / acta Journal Compilation © 2017 Acta Dermato-Venereologica.