Conditional learning is an important component of our everyday activities, e.g. handling a phone or sorting work files and requires identification of the arbitrary stimulus, accurate selection of the motor response, monitoring of the response, and storing in memory the stimulus-response association for future recall. Learning this type of conditional visuo-motor task appears to engage the premotor dorsal region (PMd). However, the extent to which PMd might be involved in specific or all processes of conditional learning is not well understood. Using transcranial magnetic stimulation (TMS), we demonstrate the role of human PMd in specific stages of learning of a novel conditional visuo-motor task that required subjects to identify object center of mass using a color cue, and apply appropriate torque on the object at lift onset to minimize tilt. TMS over PMd, but not vertex, increased error in torque exerted on the object during the learning trials. Analyses of digit position and forces further revealed that the slowing in conditional visuo-motor learning resulted from impaired monitoring of the object orientation during lift, rather than stimulus identification, thus compromising the ability to accurately reduce performance error across trials. Importantly, TMS over PMd did not alter production of torque based on the recall of learned color-torque associations. We conclude that the role of PMd for conditional learning is highly sensitive to the stage of learning visuo-motor associations.
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