Cerebellar transcranial magnetic stimulation impairs verbal working memory

Previous functional magnetic resonance imaging and patient studies indicate cerebellar participation in verbal working memory. In particular, event-related functional magnetic resonance imaging showed superior cerebellar activation during the initial encoding phase of the Sternberg task. This study used functional magnetic resonance imaging-guided transcranial magnetic stimulation (TMS) to test whether disruption of the right superior cerebellum (hemispheric lobule VI/Crus I) impairs verbal working memory performance. Single-pulse TMS was administered immediately after letter presentation during the encoding phase on half the trials. Sham TMS and a Motor Control task were included to test for general distraction and nonmemory-related motor effects. Results showed no effects of TMS on accuracy, but reaction times (RTs) on correct trials were significantly increased on TMS relative to non-TMS trials for the Verbal Working Memory and Motor Control tasks. Additional analyses showed that the increased RT was significantly greater for Verbal Working Memory than for the motor task, suggesting that the effect on working memory was not caused by interference with finger responses. Sham TMS did not affect RTs, indicating that the potentially distracting effects of the posten-coding click did not contribute to the increase in RT. The observed effects from cerebellar disruption are consistent with proposed cerebrocerebellar involvement in verbal working memory.