Direction of handedness linked to hereditary asymmetry of a sensory system.

Studies on the role of heredity in the transmission of handedness in nonhuman mammals have, so far, led to the isolation of mouse strains that differed in the lateralized versus ambidextrous use of the forepaw in a food-retrieval task (strength of paw preference). Here we report that left versus right use of the forepaw (direction of paw preference) is associated with a genetically expressed structural asymmetry of a sensory system, the whisker-to-barrel pathway. Mice that express whisker pad asymmetry of a direction that corresponds with the asymmetry for which they were bred demonstrate an opposite shift in the distribution of handedness: a right or left dominance of the whisker pad predicts a high proportion of left-handers or right-handers, respectively. Is an altered brain circuit--that is, a consequence of the asymmetry of the whisker pad--associated with a change in the circuitry that governs handedness? Or, alternatively, are there two gene sets responsible for the phenomena that we report--one that causes "whiskeredness" and another that causes handedness?