Cerebellar involvement in response reassignment rather than attention.

A number of functional hypotheses have recently been advanced to account for how the cerebellum may contribute to cognition. Neuropsychological studies suggest the cerebellum is involved in switching attentional set. We present evidence that fails to support this hypothesis. Rather, we propose that in such tasks, the cerebellum is involved with the remapping of response alternatives to different types of stimuli. In our experiment, participants fixated on the center of a screen onto which a random presentation of four visual stimuli was presented. The stimuli were grouped along two dimensions (color: red square or blue square; shape: white circle or white triangle). Participants were instructed to respond with a button press only to presented stimuli for a particular dimension (e.g., red squares), to switch between two dimensions (where the target on the attended dimension served both as a signal for a response and as an indicator to shift attention to the other dimension), or to switch attention between two dimensions but make an overt response only to targets on one of the dimensions. Using functional imaging, we identify areas of lateral cerebellar cortex that are recruited when subjects must reassign motor responses to different stimuli. Furthermore, we demonstrate that switching of attention between dimensions without a motor response does not produce stronger activation within the cerebellum compared with conditions involving response and attention to a single dimension. These results suggest the cerebellum is involved in response reassignment.