1074
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 .