Subcortical contributions to associative learning and cognitive control in cerebellar degeneration

Beyond motor control, the cerebellum has increasingly been implicated in cognitive functions, including inhibitory control, whereas its contribution to feedback-based associative learning remains less well established. This study investigated the structural correlates of inhibitory control and feedback-based learning of stimulus-response (S-R) associations in cerebellar degeneration, focusing on cerebellar, striatal, and hippocampal contributions. Twenty-seven patients with cerebellar degeneration and 28 age-, sex-, and education-matched healthy controls completed the Stroop test and the Concurrent Discrimination and Transfer Test (CDTT) and underwent structural magnetic resonance imaging. The CDTT comprised two phases: acquisition of S-R associations and transfer of previously acquired associations to novel stimulus combinations. Patients showed significantly reduced right caudate volume, impaired inhibitory control, and impaired feedback-based S-R acquisition, characterized by slower acquisition and increased acquisition errors. Among participants who reached the acquisition criterion, no significant between-group difference in transfer performance was detected. In patients, Stroop interference time was negatively correlated with right hippocampal volume. Acquisition error rate was negatively correlated with left and right hippocampal and right putamen volumes, whereas the number of trials required to acquire S-R associations was negatively correlated with right hippocampal volume. In healthy controls, acquisition error rate was negatively correlated with bilateral cerebellar cortex volumes. Between-group analyses showed that the association between acquisition speed and right hippocampal volume differed between groups, whereas no significant interactions between group and regional brain volumes were observed for acquisition error rate. Together, these findings indicate impaired inhibitory control and feedback-based S-R acquisition in cerebellar degeneration. The findings support a distributed systems account of cognitive dysfunction in cerebellar degeneration and highlight differential associations of cerebellar, striatal, and hippocampal volumes with feedback-based S-R learning.