Motor learning

The predictions intrinsic to feed-forward operation should be learnt during several trials attempting to execute the task. This is motor learning and is perhaps significant in obtaining skill in all voluntary motor tasks, involve learn to walk.

In one model of motor learning (the cerebellar feedback-error-learning model) the cerebellum obtains a program known as inverse model of the motor task that is the transformation from the preferred trajectory to the motor commands required to bring about the movement as shown in figure. In this model movement errors are originally represented as sensory errors. For illustration, during a tennis match a wrong arm movement will be visually apparent from the direction of the ball, and an fault in playing a musical instrument will sound wrong. Sensory errors are transformed into a neural firing pattern which identifies errors in motor presentation, an operation of the inferior olivary nucleus. The inferior olive sends these motor error signals to the cerebellum through the olivocerebellar tract climbing fibers as shown in figure below. Therefore, the cerebellum gets mossy fiber input which represents the desired trajectory, sensory input (example, from visual cortex or proprioceptor pathways), and feedback from the inferior olive which presents errors in the motor performance.

Figure: The operation of the inverse model on the controlled system turns a preferred into an actual trajectory. The superior the inverse model the closer the actual is to the preferred trajectory.

Figure: A model for motor learning by the cerebellum. Whenever the cerebellum is operating in feed-forward mode the bold pathway is activated. Here, cf=climbing fibers; and mf=mossy fibers.

The error signals carried by the climbing fibers causes concurrent mossy fiber input to become less efficient in activating Purkinje cells. When the similar pattern of mossy fiber input takes place consequently, the Purkinje cells fire fewer simple spikes and cause less inhibition on downstream motor pathways. This accurates the motor output. The cellular method which alters the responsiveness of the Purkinje cells is extended term depression.