Motor deficits cannot explain impaired cognitive associative learning in cerebellar patients

There is a strong evidence that the cerebellum is involved in associative motor learning. The exact role of the cerebellum in motor learning, and whether it is involved in cognitive learning processes too, are still controversially discussed topics. A common problem of assessing cognitive capabilities of cerebellar patients is the existence of additional motor demands in all cognitive tests. Even if the patients are able to cope well with the motor requirements of the task, their performance could still involve compensating strategies which cost them more attentional resources than the normal controls. To investigate such interaction effects of cognitive and motor demands in cerebellar patients, we conducted a cognitive associative learning paradigm and varied systematically the motor demands and the cognitive requirements of the task. Nine patients with isolated cerebellar disease and nine matched healthy controls had to learn the association between pairs of color squares, presented centrally on a computer monitor together with a left or right answer button. In the simple motor condition, the answer button had to be pressed once and in the difficult condition three times. We measured the decision times and evaluated the correctly named associations after the test was completed. The cerebellar subjects showed a learning deficit, compared to the normal controls. However, this deficit was independent of the motor difficulty of the task. The cerebellum seems to contribute to motor-independent processes, which are generally involved in associative learning.