 The illusion is demonstrated by positioning the middle finger in cold water and the ring and index fingers in warm water.Due to shortcomings in the body map - multisensory representation of the body - and this particular sensory input configuration, the brain is tricked into thinking the middle finger is in the warm water and the index and ring fingers in cold water.In an fMRI experiment of the illusion, researchers recently observed an activation of the thalamus not seen for control stimuli.