Training and synchrony in the motor system.

Two monkeys trained for >5 years to perform 12 finger and wrist movements had both a greater prevalence of motor cortex neurons with significant effects in spike-triggered averages and a greater ratio of synchrony effects to pure postspike effects than a monkey trained <1 year to perform six movements. By comparison, stimulus-triggered averages were generally similar in all three monkeys, indicating that the increased prevalence of synchrony in spike-triggered averages was a feature of voluntary motor system activity in the monkeys trained for a longer period of time. Synchronization among neurons with relatively direct connections to spinal alpha-motoneuron pools, including motor cortex neurons, may increase as a repertoire of skilled movements is acquired and practiced during long-term training.