Abstract
There are some unresolved problems in motor learning theory. One is determining the source of a learning signal, sometimes called a motor error signal. Another one is the credit assignment problem of the motor error, since the erroneous performance perceived by a subject is due to the actions of many elementary motor units. The feed-forward associative learning theory attributes the source to the movement system itself. When a subject performs a corrective movement after his primary movement, the proposed neural learning device learns to associate the primary motor command with the corrective motor command by using a place-coding system. In the subsequent trials, the primary movement will involve a correction due to the participation of this mechanism, thus resulting in better performance. The device consists of many adaptive units each of which is specialized for a particular elementary motor unit, and naturally resolves the assignment problem. The theory assumes three conditions, namely, that a motor center and the learning device share the same place-encoded motor information; the motor center issues a command and a learning signal simultaneously from the same unit; and a learning signal issued with a corrective command has a heterosynaptic interaction with the previous primary command. The cerebellum is a reasonable candidate for the device satisfying these conditions. The reaction time of a corrective movement, usually 100-300 ms, almost satisfies the coincidence condition for long-term depression of the granule-to-Purkinje synapses. As an application, this theory is demonstrated to account for behavioral results regarding saccadic adaptation. [J Physiol Sci. 2006;56 Suppl:S43]
