Image: Marion et al.
Researchers from Trinity College Dublin used EEG monitors to scan the brain of musicians while they listened to a piece of music and imagined a piece of music they knew. The study found that the brain's electrical activity for listened music and imagined or expected music was the same except for being of opposite voltage. When the listened music matched the expected music in the brain, the positive and negative signals cancel each other out. However when the music doesn't match what the brain is predicting or expecting, the brain reacts to the mismatch.
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