Red hot chilli peppers are a must for curry connoisseurs, but leave the mouth burning and eyes watering. The active ingredient is capsaicin that triggers pain receptors in the mouth and skin, sending electrical signals to the brain that register as pain. People with neuropathic pain experience the same prickly burning pain, incessantly. Neuropathic pain has no obvious cause, but is a common side-effect of nerve damage and can cause hypersensitivity to other pain stimuli such as heat. Here, MRI scans of the side (top left), back (bottom left) and top (right) of the head show which brain areas become activated when a heat stimulus is applied to the arm. Heat alone activates areas marked blue, but when capsaicin is first applied briefly to the skin, activation spreads into the red (overlapping areas, purple). Capsaicin-induced pain could provide a new model to test novel pain-killers for neuropathic pain.
Written by Caroline Cross
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