Response Synchrony, APG Theory, and Motor Control
The plausibility of using response synchronization as a mechanism for binding in the motor system is examined. The theoretical and experimental arguments for using response synchrony to solve the binding problem in movement control are first reviewed. Both types of arguments fail to present a convincing case because, response synchrony does not correlate well with routine muscle activation, does not account for the existence of command-neuron burst discharges (in motor cortex and magnocellular red nucleus), and can only be associated with tasks that involve continuous feedback control or with difficult and attention-demanding situations. An alternative theory known as the Adjustable Pattern Generator Theory (APG Theory; Houk, 1987) is presented as a candidate which would account for movement command generation and is consistent with available experimental evidence. IT is possible that motor cortical response synchrony is a complementary mode of operation to that described by the APG Theory, as the associated cortical synchrony and command burst discharge seem to occur under different circumstances. The key differences between these mechanisms are also highlighted.