MGH Martinos Center for Biomedical Imaging 2016 | Page 24

new insights into the brain Why We Itch When Other People Scratch An fMRI Study Vitaly Napadow and colleagues got to the root of this nagging question The study supports a growing body of literature that suggests “your perception is indeed your reality,” said Napadow. We know from research, and from everyday life, that an itch can be contagious. We tend to feel itchy when we see people scratch—or even, as studies have shown, when we hear them talk about an itch. What we don’t fully understand, from a neuroscience perspective, is why. In other words: Studies have confirmed that itch can be induced and modulated by cognitive and emotional factors, as well as by placebo and nocebo effects (a nocebo is essentially a negative placebo, an aversive response to an inert stimulus). But the brain activity underlying this has, thus far, remained elusive. water. During each, the researchers performed fMRI scans of what was going on in the patients’ brains. The results demonstrated that the nocebo—the saline thought to be an allergen—produced a greater A team of researchers at the MGH itch sensation than the open saline Martinos Center and collaborators control, with greater fMRI signal inat other institutions looked into this c reases in brain regions associated question of the imagined itch in pa- with motivational, attention and tients suffering from chronic itch. cognitive processing. In a paper published in November 2015 in the journal Allergy, they re- Notably, these responses correlated with responses in near identical ported what they found. brain regions to a real allergen obThe study looked at a cohort of served in the same patients. This patients clinically diagnosed with suggested that the brain circuitry atopic dermatitis, a type of inflam- activated by the real allergen also mation that leads to swollen and comes into play with the imagined, cracked skin. The patients received nocebo-induced itch. two saline skin pricks: one in which they thought the saline was actu- The upshot? The study supports a ally an allergen that would cause growing body of literature that sugitchiness and the other where they gests “your perception is indeed knew the saline was a simple drop of your reality,” said Vitaly Napadow, an Associate Professor of Radiology at Harvard Medical School, a Martinos Center investigator and corresponding author of the Allergy paper. If you think you feel itchy after a skin prick with saline—as opposed to a real allergen—then your brain responds in the same way it would for the allergen. “Our brains have an amazing capacity to recreate the world around them,” he said, “even without the afferent stimulus we think is necessary to produce a certain sensation.” Beyond such questions of perception and reality, the findings also have important clinical implications. They suggest, Napadow said, that brain-based therapies can be used to effectively down-regulate itch perception in chronic itch patients, to a greater degree than previously thought. The investigators are now looking into further studies in which they would assess the potential of specially tailored cognitive / affective therapies for this end.